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Article

Sugar Metabolism and Transport in Response to Drought–Rehydration in Poa pratensis

by
Jiangdi Yu
1,
Ran Zhang
1,2,*,
Xiaoxia Li
1,2,
Di Dong
1,2 and
Sining Wang
1,2
1
Institute of Ecological Protection and Restoration, Chinese Academy of Forestry, Beijing 100091, China
2
Grassland Research Center, National Forestry and Grassland Administration, Beijing 100091, China
*
Author to whom correspondence should be addressed.
Agronomy 2025, 15(2), 320; https://doi.org/10.3390/agronomy15020320
Submission received: 24 December 2024 / Revised: 17 January 2025 / Accepted: 21 January 2025 / Published: 27 January 2025
(This article belongs to the Section Plant-Crop Biology and Biochemistry)
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Versions Notes

Abstract

:
Poa pratensis is one of the world’s most widely planted cold-season turfgrasses, with good quality but poor drought resistance. When plants suffer from stress, the metabolism of soluble sugar takes place, which is a dynamic process involving both degradation and synthesis. A detailed and in-depth study of the sugar metabolism process in plants’ response to stress will help us to understand the internal mechanism of plant adaptation to stress. In this study, the ‘10-202’ ecotype with drought resistance and the ‘Blue moon’ ecotype with drought sensitivity were used to explore the sugar metabolism process in response to drought stress. The results showed that drought stress induced sucrose accumulation in the leaves and roots, promoted increases in SPS, S-AI, and PpN/A-Inv activities, as well as gene expression in the leaves, and changed the content and distribution of fructose, glucose, sucrose, maltose, and trehalose in vivo. Compared with ‘Blue moon’, ‘10-202’ had higher trehalose content in leaves under normal conditions, and its roots could accumulate more fructose and glucose to maintain the balance of osmotic potential and redox under drought stress. Meanwhile, PpSWEET1b, -12, and -15 in the leaves and roots of the two ecotypes were significantly induced by drought stress. The improvements in sucrose accumulation and decomposition efficiency in leaves under drought stress is conducive to enhancing drought resistance in plants. PpSWEET1b plays a vital role in regulating the sugar transport process of drought tolerance in turfgrass.

1. Introduction

Soluble sugars are considered to be the main osmotic regulator in plants. Previous studies have shown that soluble sugars play an important role in maintaining the overall structure and growth of plants, for example, by providing energy for plant growth and development; as precursors of metabolism; as short- and long-distance signaling molecules (glucose, sucrose, fructose, trehalose, etc.) [1]; and by playing a role in osmotic protection in plants under stress as part of the reactive oxygen species (ROS) scavenging system [2,3]. Previous studies have revealed that glucose can induce the stomatal closure of seedlings, reduce photosynthesis rate, maintain leaf water content and osmotic regulation, prevent cell membrane oxidation, and enhance plant adaptability to drought and salt stress [4]. In addition, glucose also regulates glycolysis and glucose metabolism under stress conditions through the target of rapamycin kinase protein (TOR) kinase signaling cascades [5].
Sucrose is the most common and crucial osmotic protection agent in higher plants [6], and its accumulation, gene expression, and metabolism are related to abiotic stress response [7]. Studies on Arabidopsis show that to cope with the effects of stress, cold-tolerant Arabidopsis seedlings displayed higher sucrose content than cold-sensitive plants under low-temperature stress [8]. Sucrose phosphate synthase (SPS) is a key rate-limiting enzyme in sucrose synthesis [9]. Previous research has found that low-temperature induction can increase SPS enzyme activity, thereby accelerating the synthesis and accumulation of sucrose in plants [10]. Abiotic stress can also induce sucrose catabolism enzymes such as invertase (INV) and sucrose synthase (SS), which produce glucose, fructose, and uridine diphosphate (UDP)-glucose. Roitsch et al. [11] showed that extracellular INV activity was significantly increased under salt stress to supply carbohydrates to sink organs. Furthermore, trehalose is shown to maintain membrane integrity, scavenge ROS, and protect protein structures by forming an amorphous glass structure around polar phospholipids groups, or by hydrogen bonding with amino acids [12], which is closely related to abiotic stress reactions [13].
Sugars cannot be transported independently through the biological membrane system and need the assistance of corresponding sugar transporters [14]. The SWEETs (sugars will eventually be exported transporters) gene family represent a kind of bidirectional transmembrane transport protein that is independent of environmental pH value and can transport sugar along a concentration gradient, thereby participating in the transportation and distribution of photosynthetic plant products [15]. SWEET sugar transporters are involved in many plant functions, including sugar transport, nectar production, seed and pollen development, leaf senescence, host-pathogen interactions, and responses to abiotic stresses [16]. It was found that environmental factors such as cold and drought could induce the expression of SWEET sugar transporter genes in plants, thereby increasing the activity of sugar transporters and rapidly increasing the content of soluble sugars (such as sucrose, fructose, glucose, or galactose) in tissues. In tea plants, cold stress significantly inhibited the expression of CsSWEET2, -3, and -16, while sharply increasing the expression of CsSWEET1 and CsSWEET17 [17]. Many SWEET sugar transporter genes in leaves, roots, and fruits changed significantly under high-sugar, high-salt, high-temperature, and low-temperature conditions [18]. AtSWEET17 in Arabidopsis is located in the vacuole membrane. Under low-temperature stress, the fructose accumulation in plant vacuoles was 2–10 times that of the control in [19].
Plants are often exposed to alternating wet and dry environments, which is also the main water environment characteristic of plant growth in semi-arid areas. The ability of plants to quickly recover from damage during drought and to adapt to continuous changes in rehydration after drought is an important feature of their adaptation to stress. Poa pratensis is one of the world’s most widely planted cold-season turfgrasses, with good quality but poor drought resistance. During the growth stage of Kentucky bluegrass, seedlings are in the most vulnerable stage of soluble sugar fluctuation and are excellent materials for studying the effects of different environmental stresses. In our previous work, we obtained the wild germplasm ‘10-202’ with drought resistance and ‘Blue moon’ (BM, Poa pratensis cv. Blue moon) with drought sensitivity, and 13 PpSWEETs sugar transporters of Poa pratensis were identified [20,21]. Here, we explore the characteristics of the accumulation, transport, and distribution of soluble sugars in Kentucky bluegrass in response to drought stress, clarify the function of plant non-structural carbohydrates in response to stress, and provide theoretical support and new research ideas for drought resistance breeding and the genetic improvement of turfgrass.

2. Materials and Methods

2.1. Plant Growth Conditions and Treatments

Here, ‘10-202’ and ‘BM’ were used as test materials. Among them, ‘10-202’ was collected from the Qinghai–Tibet Plateau at an altitude of more than 2400 m in September 2010 and preserved in the Academy of Animal Sciences and Veterinary (Qinghai University, Xining, China).
The experiment was conducted by pot culture in a growth chamber on 15 June 2020. Vermiculite and nutrient soil were mixed at a volume ratio of 3:1 and then used as soil matrix. The seeds were soaked in a seedling tray. After 20 days of growth, the seedlings with uniform growth were selected and transplanted into pots (diameter: 18 cm; 16 seedlings per pot). Forty-eight pots were divided into control and drought treatment groups, comprising two accessions (that is, 24 pots for each accession, with 12 pots allocated to each treatment). This arrangement was replicated three times, resulting in four pots per replicate. The seedlings were grown at 25/20 °C (day/night) and relative humidity of 65%, with a 16 h illumination time and a luminous flux density of 400 μmol·m−2·s−1. The seedlings were watered every three days to keep the soil wet, and the seedlings were treated after 35 days of growth (four-leaf stage). We irrigated three control pots every day at the same time to keep the soil wet. Water was withheld in the other nine pots (i.e., natural drought stress) for 6 days until the rolling leaf phenotype was observed. For more severe drought treatment, water was withheld for another 6 days, which resulted in severe leaf rolling. The 12 days drought-treated samples were then rewatered for each time point (i.e., 6 days drought, 12 days drought, and 1 day water recovery and 5 days water recovery).

2.2. Treatments and Sampling

Leaves and roots were collected at 6 d and 12 d after drought stress and at 1 d (R1 d) and 5 d (R5 d) of recovery after drought stress to determine sugar content and enzyme activity. The relative water content (RWC) and electrolyte leakage rate (EL) of the leaves were also determined. Some samples were rapidly frozen in liquid nitrogen and stored at −80 °C for RNA extraction, with three biological repeats for each treatment.

2.3. Determination of RWC and EL of the Leaves

The RWC of the leaves was measured at 9:00 a.m.; 0.2 g of fresh leaves were weighed and recorded as fresh weight (FW). The leaves were then soaked in distilled water overnight. After absorbing surface moisture, the saturated weight (TW) was weighed. The saturated blades were then placed into the oven to dry until a constant weight, following which the dry weight (DW) was determined by weighing. The RWC of the leaves was calculated as follows: RWC = (Fw − Dw)/(Tw − Dw) [22].
For the EL: 0.2 g FW were weighed and placed in a test tube, shaken, and soaked them distilled water overnight, and then we measured the initial conductivity (Ci) of the liquid using a conductivity meter. We heated the test tube in water to 120 °C for 20 min. After cooling, we shook it again overnight and then measured the maximum conductivity (Cmax) and calculated the EL; the calculation formula is EL (%) = Ci/Cmax [23].

2.4. Measurement of Sugar Contents

Leaf and root tissues (1.0 g DW) of Kentucky bluegrass were homogenized with 20 mL deionized water. The homogenate was transferred to centrifuge tubes and incubated in a water bath at 100 °C for 1 h and centrifuged at 10,000 rpm for 20 min. Then, the extract was filtered and transferred to a new 50 mL centrifuge tube, and 20 mL deionized water was added to the residue. The extraction steps were repeated. After mixing two filtered extracts, the extract was boiled to about 1 mL at 100 °C and deionized water was added to a constant volume of 5 mL. Filtered by 0.45 μm filter membrane, the supernatant was used as soluble sugar extract to determine the contents of maltose, sucrose, trehalose, glucose, and fructose [24].
A high-performance liquid chromatography–refractive index detector (HPLC-RID) was used to determine the carbohydrate content of each sample. The high-performance liquid chromatography (Agilent 1100, Palo Alto, CA, USA) was equipped with a refractive index detector (Agilent 1100, Palo Alto, CA, USA). An amino chromatographic column (XB-NH2 column, 250 mm × 4.6 mm, 5 μm, Shimadzu, Kyoto, Japan) was used, and the mobile phase consisted of acetonitrile–water (70:30; V:V), column temperature was 30 °C, flow rate was 1.0 mL·min−1, and the injection volume was 20 μL.
The peak times of fructose, glucose, sucrose, maltose, and trehalose in the standard samples were 6.977 min, 8.073 min, 10.758 min, 12.353 min, and 13.309 min, respectively (Table 1). The absorption peaks were well separated without interference. The standard solution of five sugars was gradually diluted. Under optimized chromatographic conditions, the regression equation and correlation coefficient were calculated with the peak area as ordinate (Y) and standard sample concentration as abscissa (X, mg·mL−1). The linear correlation coefficients of fructose, glucose, sucrose, maltose, and trehalose were 0.9941, 0.9965, 0.9952, 0.9967, and 0.9946, respectively. The extraction method and chromatographic conditions in this experiment were reliable.

2.5. Determination of Starch Content

Starch content was determined following the method of Kuai et al. [25]. The ethanol-insoluble residue was added to 2 mL distilled water and incubated in a boiling water bath for 15 min. Starch was hydrolyzed into the sample with 9.2 mol·L−1 perchloric acid. The content of starch was determined spectrophotometrically with anthrone reagent at an A620 nm wavelength.

2.6. Determination of Enzyme Activity

Leaf and root tissues of 0.5 g FW were used to measure the activities of sucrose phosphate synthase (SPS; EC 2.4.1.14), sucrose synthase (SS; EC 2.4.1.13), soluble acid invertase (S-AI; EC 3.2.1.26), and neutral/alkaline invertase (N/A-Inv; EC 3.2.1.26). The analysis was repeated three times on each sample. The determination method is the same as that reported in our previous study [26].

2.7. Gene Expression Analysis

Total RNA was extracted by an RNA simple Total RNA Kit (centrifugal column type) from Tiangen Biotech Limited (Beijing, China). cDNA was then synthesized using PrimerScript RT Kit (TaKaRa, Dalian, China). Real-time quantitative PCR (qRT-PCR) was conducted using a LightCycler® 96 System (Roche, Shanghai, China) and performed using a SuperReal PreMix Plus (SYBR Green) fluorescence quantitative kit (Tiangen, Beijing, China). A more thorough description of the qRT-PCR procedure is provided in one of our previous publications [20]. Gene-specific primers for SPS, SS, S-AI, N/A-Inv, cell wall invertase (CWINV), PpSWEETs, Actin (ACT), and S-Adenosylmethionine decarboxylase (SAM) were designed and synthesized to detect gene expression in Kentucky bluegrass based on the sequences in NCBI, as shown in Table S1. A total of three biological replicates and two technical replicates were performed. The relative expression levels were standardized with actin and evaluated using the comparative 2−ΔΔCt method [27].

2.8. Study on the Complementary Absorption of Sugar Substrates by Yeasts PpSWEET1b, -12, and -15 in Poa pratensis

The full-length coding sequences of PpSWEET1b, -12, and -15 were amplified (Table S2) and cloned into the pDRTXa vector. The fusion cloning primers of the PpSWEETs gene combined with yeast expression vector are shown in Table S3. We transformed recombinant vector plasmids into yeast strain EBYVW4000 receptive cells using the PEG/LiAc method.
The yeast transformation system included 36 μL LiAc (1.0 M), 240 μL 50% (w/v) PEG3500, 50 μL salmon sperm DNA (2 mg·L−1), 1 μL plasmid DNA, and 33 μL ddH2O. The reaction program was incubated in a 42 °C constant temperature water bath for 50 min. After incubation, it was centrifuged at 15,000 rpm for 1 min. After removing the supernatant, we resuspended the bacterial cell pellet with 1 mL sterile deionized water, and then a pipette of 50 μL was applied to SD/ura screening medium (SC/ura medium with 2% maltose added) and then it was incubated upside down at 28 °C for 3 d [28].

2.9. Yeast Recombinant Vector Plasmids pDRTXa-PpSWEETs for Transport and Absorption of Different Sugar Substrates

We replaced 2% maltose in SD/ura screening medium with 2% sucrose, 2% mannose, 2% fructose, 2% galactose, and 2% glucose to verify the transport and absorption function of PpSWEETs sugar transporter genes on different sugar substrates. The bacterial solution gradients of OD600 concentration were 1 (original solution), 0.1, 0.01, and 0.001.

2.10. Data Analysis

All the data were analyzed by SPSS 24.0 Windows version (SPSS Inc., New York, NY, USA), and the average value and standard error (SD±) were used to express the determination results. A t-test was used for the control and treatment group among the same materials, and GraphPad Prism 8.0.2 was used for mapping. We used the software package ggplot2 3.3.5 in R language 4.1.0 to draw heatmaps [29].

3. Results

3.1. Physiology Characterization of Poa pratensis Under Drought–Rehydration Treatment

Continuous drought stress can lead to dehydration and wilting of plant leaves, and the RWC of leaves reflects the water status and wilting degree of plants. As shown in Table 2, the leaf RWC of the control group was more than 85% during the experiment in both ecotypes. A significant decrease in RWC was detected at 6 d of drought stress in ‘BM’, while no obvious change was detected in ‘10-202’, which exhibited strong drought resistance. After 12 days of drought treatment, the RWCs of both ecotypes were markedly reduced compared with the control. The RWC of the leaves of ‘10-202’ was 52%, and the RWC of the leaves of ‘BM’ was only 31%. After rewatering, the R1D and R5d of the two ecotypes increased immediately.
The value of EL reflects the permeability of plant cell membrane, and the greater the degree of damage, the higher the degree of electrolyte leakage in plant leaves. As shown in Table 2, drought stress can lead to a significant increase in EL in the leaves of Poa pratensis. Throughout the entire drought stress and rehydration stage, the EL value of ‘Blue moon’ leaves was significantly higher than other treatments.

3.2. Physiological Response of Sugar Metabolism of Poa pratensis Under Drought–Rehydration Treatment

For monosaccharides, under normal watering treatment, the content of fructose in the leaves of ‘Blue moon’ was higher than that of ‘10-202’, while the content of glucose was just the opposite (Figure 1a,c). Drought stress remarkably decreased the fructose and glucose content in the leaves of ‘Blue moon’, while the root’s fructose and glucose contents increased (Figure 1b,d). The fructose content in the leaves of ‘10-202’ increased remarkably after 12 d of drought stress and remained at a high level after rewatering (Figure 1a). In addition, drought stress also significantly increased the fructose and glucose contents in the roots of ‘10-202’ (Figure 1b,d). After 5 d of rewatering, the glucose content in the leaves of ‘10-202’ increased remarkably, while that of ‘Blue moon’ returned to the normal level (Figure 1c).
As shown in Figure 1e,f, the sucrose content of leaves and roots in both ecotypes increased progressively with the extension of drought stress time. When the stress lasted for 12 d, the sucrose content in the leaves of ‘Blue moon’ was 5.63 times of the control treatment, and that of the leaves of ‘10-202’ also increased significantly, but the increased value was lower than that of ‘Blue moon’. In addition, the sucrose content of roots was lower than that of leaves. In the whole drought–rewatering process, the root sucrose content of the two ecotypes was higher than that of the control level.
The leaf maltose content of both ecotypes increased significantly under drought stress. It continued to enhance at 1 d after rehydration, which was 5.52 times (‘Blue moon’) and 2.59 times (‘10-202’) of the control treatment, respectively. After rehydration for 5 d, the leaf maltose content tended to decrease (Figure 1g). After 12 d of drought stress, the maltose content in the roots of ‘Blue moon’ increased greatly, while the maltose content in the roots of ‘10-202’ decreased obviously. After 5 d of rewatering, the maltose content in the roots of the two ecotypes increased sharply again (Figure 1h).
The trehalose content in leaves was significantly lower than that of other soluble sugars, and the trehalose content of ‘10-202’ was higher than that of ‘Blue moon’ at normal treatment (Figure 1i). With the prolonged drought treatment, the trehalose content in the leaves of the two ecotypes showed a continuous increasing tendency, and the trehalose content of ‘10-202’ was the highest after 12 d of drought stress, which was 0.74 mg·g−1. The trehalose content in the roots of the two ecotypes was noticeably lower than that of the control at 12 d of drought stress. After 1 d of rehydration, the trehalose content in the roots of ‘Blue moon’ increased noticeably, which was 3.15 times the control (Figure 1j).
It can be seen in Figure 2 that under the condition of no drought treatment, the leaves and starch content of the two materials were different, indicating that there are differences in starch content among varieties, and the starch content of ‘10-202’ is higher than that of ‘Blue moon’. Under drought stress, the starch content was significantly lower than that of the control treatment. After 5 days of rehydration, the starch content gradually increased, and the starch content in the leaves gradually returned to the control level.
Drought stress remarkably increased the SPS activity in the leaves and roots of two Kentucky bluegrasses. During the whole rehydration progress, the SPS activity of both was still higher than that of the control (Figure 3a,b).
The SS activity in the leaves and roots of ‘10-202’ showed a positive upward trend during the whole period of drought stress (Figure 3c,d). Nevertheless, a significant decline in SS activity was observed in the leaves of ‘Blue moon’ under drought stress. The activity of SS in the roots of ‘Blue moon’ increased at first and then decreased, and there was no sign of recovery after rehydration (Figure 3d).
The change in trends of S-AI activity and N/A-Inv activity in leaves of the two ecotypes were entirely consistent under drought stress. The activities of S-AI and N/A-Inv in the leaves of ‘Blue moon’ and ‘10-202’ were increased after 12 d of drought stress (Figure 3e,g). However, in roots, drought stress decreased the activity of S-AI and increased N/A-Inv. The S-AI activity of ‘10-202’ roots was also remarkably higher than that of the control during the whole period of drought stress, but the N/A-Inv activity did not remarkably change (Figure 3f,h).

3.3. Expression Patterns of Sucrose Metabolism and Transport Genes in Poa pratensis Under Drought–Rehydration Treatment

The expression of PpSPS in the leaves and roots of both ecotypes was significantly up-regulated during drought stress and rewatering period (Figure 4a,b).
After 12 d of drought stress, the expression of PpSS in the leaves of ‘Blue moon’ was significantly up-regulated compared with the control treatment, about 3.54-fold (Figure 4c). However, a clear inhibition of PpSS expression was discovered in roots. The expression level of PpSS in roots of ‘10-202’ was inhibited after 12 d of drought stress, but increased sharply after 1 d of recovery (Figure 4d).
The expression levels of PpS-AI in the leaves of ‘Blue moon’ showed an upward trend during the whole period of drought stress, which were 4.18 and 31.15 times higher than that of the control, respectively. The relative expression level of PpS-AI in the leaves of ‘10-202’ was down-regulated first and then remarkedly up-regulated with the extension of stress time, and it still maintained a high expression level 1 d after rehydration. (Figure 4e). After 6 d of drought stress, the expression of PpS-AI in the roots of ‘Blue moon’ was remarkably down-regulated, while that in the roots of ‘10-202’ was up-regulated (Figure 4f).
The expression level of PpCWNIV in the leaves and roots of both ecotypes was significantly up-regulated under drought stress (Figure 4g,h). After rehydration, the relative expression of PpCWNIV in the leaves was still positively up-regulated (Figure 4h).
The expression of PpN/A-Inv in the leaves and roots of ‘Blue moon’ was significantly up-regulated under drought stress, and the relative expression amounts were 2.84 and 15.17 in the leaves, respectively. In contrast, the relative expression of PpN/A-Inv in the leaves of ‘10-202’ was significantly down-regulated after 6 d of drought stress (Figure 4i). Meanwhile, the relative expression of PpN/A-Inv in the roots of ‘10-202’ was less affected (Figure 4j).
As shown in Figure 5a, the expression multiples of several PpSWEET family genes in the leaves and roots of ‘Blue moon’ increased significantly with the extension of drought treatment time. After 12 d of drought stress, the genes with higher expression multiples in the leaves were PpSWEET15, -12, and -1b, and the log2 fold change values were 10.59, 10.43, and 7.79, respectively. In ‘10-202’ (Figure 5b), half of the PpSWEETs genes in the leaves were down-regulated at 6 d of drought stress. On the 12th day of drought stress, most genes were significantly up-regulated, and the genes with the highest expression multiples were PpSWEET15, -12, and -4, and the log2 fold change values were 9.25, 9.00, and 7.30, respectively. The expression pattern of multiple genes in roots was also up-regulated under drought stress. The genes with higher expression levels were PpSWEET12, -1b, -16, and -15 after 12 d of drought stress. It was detected that the expression level decreased significantly after rewatering. Comprehensive analysis showed that under long-term drought stress, the expression level of PpSWEETs genes in the leaves of the two ecotypes was higher than that those in the roots, and the expression levels of PpSWEET1b, -12, and -15 in two Kentucky bluegrasses were higher in response to drought stress.

3.4. Functional Verification of PpSWEET1b, -12, and -15 in Yeast Substrate Absorption Complementarity

pDRTXa-PpSWEET1b, pDRTXa-PpSWEET12, pDRTXa-PpSWEET15, and pDRTXa were transformed into yeast EBYVW4000 receptor cells. The transformed yeast was obtained through SD/ura screening medium using maltose as substrate. Using a 2% maltose tablet as the positive control and pDRTXa empty as the negative control, the positive results showed the presence of the expression vector and target genes. The vector construction and transformation results were successful. In addition, the results showed that they could grow well and slowly on the medium containing galactose, which were not significantly different from the empty control, and they could not grow on the medium containing mannose. However, pDRTXa-PpSWEET1b transgenic yeast could grow well on SD/ura medium containing glucose and sucrose, but had limited growth on SD/ura medium with fructose as substrate. pDRTXa-PpSWEET12 and pDRTXa-PpSWEET15 transgenic yeasts were unable to resume growth on glucose, sucrose, fructose, and mannose plates (Figure 6), indicating that their encoded proteins cannot absorb and transport these sugars in yeast. The transport properties still need further confirmation.

4. Discussion

Coordination between carbon supply and utilization is essential for plant growth and development [30,31]. Carbohydrates in plants exist in various forms, and non-structural carbohydrates, as important reactants in plant life activities, participate in the process of plant metabolism. Studies have shown that drought stress can reduce the photosynthetic rate of plants, inhibit the synthesis of photosynthates, and change the distribution and metabolism of carbon in plants, resulting in physiological metabolism disorders [32]. Xu et al. [22] found that drought stress can improve the survival rate of plants in adverse environments by changing the distribution of assimilates from photosynthetic organs (such as leaves) to heterotrophic organs (such as roots and seeds). Therefore, sugar accumulation in plant organs induced by drought stress may be involved in the regulation of carbohydrate metabolism and sugar transport.
Soluble carbohydrates can not only be used as an energy source for plant growth and development, but also play an essential role in osmotic regulation when plants are subjected to stress, maintaining the balance of cell osmotic pressure, stabilizing the active conformation of enzyme molecules in cells, and improving cell water retention capacity. The determination of soluble sugar content in the leaves and roots of soybean seedlings under drought stress showed that the leaves of soybean seedlings accumulated higher sucrose and soluble sugar content than the roots, indicating that they may promote sucrose from leaves to roots to adapt to drought stress by increasing leaf phloem load [31]. The results of this study showed that the sucrose content in the leaves and roots of the two Kentucky bluegrasses increased to different degrees under drought stress, and the sucrose content in the leaves was much higher than that in the roots, which was consistent with the previous research results. In addition, Du et al. [31] found that sucrose content showed a gradual upward trend with the extension of drought stress time. This is consistent with the results of this study. Studies have shown that the accumulation of sucrose in plant leaves caused by stress may be due to its promotion of callose synthesis and precipitation, blocking vascular bundles, and thereby affecting the direct transport capacity of sucrose [33], which may also be one of the reasons for the increase in sucrose content in the leaves and roots of two Kentucky bluegrasses under drought stress.
In this study, we found that the effects of drought stress on fructose and glucose in the leaves and roots of Poa pratensis were different. The contents of fructose and glucose in the leaves of ‘Blue moon’ showed a decrease with the extension of drought time, which may be due to the severe drought stress damage to the arrangement of phospholipid bilayers on the cell membrane, resulting in changes in plasma membrane permeability, and cell shrinkage after dehydration of protoplasts and cell walls, resulting in mechanical damage and metabolic disorders [34]. The glucose content in the leaves of ‘10-202’ also decreased under drought stress. In contrast, the fructose content decreased first and then increased with the extension of stress time, which may be due to the fact that part of the sucrose accumulated in the leaves was converted into fructose and glucose. The sucrose accumulation in the leaves was lower than that in ‘Blue moon’. Under drought stress, the roots of ‘10-202’ with drought resistance accumulated more fructose and glucose than the sensitive ‘Blue moon’, better maintained the balance of its osmotic potential and redox level, and made it drought-resistant. Comprehensive analysis of the changes in sucrose, fructose, and glucose contents in the roots of two Kentucky bluegrasses under drought stress showed that effective sugar metabolism and transport capacity promoted the accumulation of soluble sugar in roots, which was consistent with previous studies [31].
Studies have shown that starch metabolism is involved in the abiotic stress response of plants. The starch content of leaves will degrade, and the biosynthesis of sugar and proline will respond to water stress [35,36]. The maltose was confirmed to be the product of β-amylase hydrolyzed starch and the main component of chloroplasts transported out at night [37]. Kaplan et al. [38] found that maltose has a protective effect on the protein cell membrane and photosynthetic system transfer chain under low-temperature stress. In this study, we found that the maltose content in the leaves was lower than that in other soluble sugars (such as sucrose, fructose, and glucose) under normal conditions. After drought stress, the content of maltose gradually increased and the starch content declined with the extension of stress time. This situation may be due to the fact that drought stress promoted the degradation of starch in the leaves, thereby promoting its transformation into soluble sugar. In addition, the study also found that ‘10-202’ accumulated higher maltose content in the leaves to adapt to drought stress than ‘Blue moon’. After rewatering, the maltose content in the leaves and roots of the two materials increased, meaning that the electron transport chains of the cell membrane and photosynthetic system were protected, and the photosynthesis of plants was restored.
Numerous studies have verified that trehalose can play an important role in osmotic regulation and the stabilization of membrane lipids. Crowe et al. [39] found that trehalose can combine water molecules with biological membranes to form hydrogen bonds during the dehydration of plant cells, thereby enhancing the drought resistance of plants. In our study, drought stress induced trehalose content in leaves of two ecotypes, and compared with ‘Blue moon’, ‘10-202’ had higher trehalose content in the leaves under normal conditions. Zhang et al. [40] measured the changes in different sugar contents in Oropetium thomaeum under different abiotic stresses. It was found that there was no noticeable difference between trehalose and control under drought and low-temperature stress, which was inconsistent with the results of this study. This may be due to differences in genotype or sampling time.
Drought stress regulates the balance of sucrose metabolism in the leaves through changes in sucrose metabolic enzyme activity [22]. However, the changes in carbohydrate metabolism-related enzyme activities varied with drought stress time, degree, and materials. Previous studies have shown that drought stress could increase SPS activity and sucrose accumulation in the leaves and stems of rice [22]. Consistent with our results, drought stress enhanced SPS enzyme activity in Kentucky bluegrass leaves and promoted sucrose synthesis. With the increased stress time, the activity of SPS increased gradually. The changing trend of SS activity in the leaves and roots of two Kentucky bluegrass cultivars was different under drought stress. The SS activity of ‘Blue moon’ in the roots increased at first and then decreased, and did not recover after rehydration, which indicates that drought stress inhibited the decomposition of sucrose in the leaves and roots of ‘Blue moon’ cultivars, and caused the accumulation of sucrose to a certain extent.
In soybean, the SPS and SS activities of leaves and roots continued to increase with the extension of stress time and the increase in stress degree under drought stress, and the expression levels of GmSPS, GmSS, GmS-AI, and GmN/A-Inv were significantly up-regulated under drought stress [31]. In addition, Zhang et al. [41] revealed that the expression of GRMZM2G139300, which encodes cell wall enzymes that hydrolyze sucrose into glucose and fructose, was up-regulated after the 6 days of drought treatment. Our data showed that drought stress up-regulated the expression of PpSPS, PpSS, PpS-AI, PpCWNIV, and PpN/A-Inv genes in the leaves of ‘Blue moon’. The expression levels of PpS-AI, PpCWNIV, and PpN/A-Inv in ‘10-202’ were also strikingly up-regulated after 12 days of stress. Consistent with previous studies, these results indicate that drought stress can promote the sucrose cycle of leaves in Kentucky bluegrass, and leaves constantly adjust their metabolic capacity to cope with drought. In addition, the increase in invertase activity also indicated that improving the ability of sucrose to convert glucose and fructose could improve the osmotic adjustment ability under drought stress. Compared with the gene expression pattern in the leaves, the expression of carbohydrate metabolism-related genes in the roots was less affected by drought stress, indicating that the improvement in sucrose accumulation and decomposition efficiency in leaves under drought stress is beneficial to enhance the drought resistance of plants. In addition, the results showed that the SPS and S-AI activities and the expression levels of PpSPS and PpS-AI were greatly affected by drought stress, indicating that the response of sucrose synthesis and decomposition in the leaves of Poa pratensis to drought stress mainly depended on the regulation of SPS and S-AI activities.
Generally, plants can regulate the redistribution of sugar in different tissues through sugar transporters to maintain the balance of osmotic potential, and improve the adaptability of plants to various adverse environments. Numerous studies have verified that SWEETs can maintain sugar homeostasis in plant organs and promote plant adaptation to drought stress [31,42]. The expression levels of nine PpSWEETs in ‘Blue moon’ leaves and five PpSWEETs in ‘10-202’ leaves increased with the increase in drought treatment duration, which suggested that drought stress responses might positively regulate these genes and increase the drought sensitivity of Poa pratensis. Particularly, the up-regulated expression of PpSWEET1b, -12, and -15 in the roots and leaves of the two ecotypes was more obvious than that of other genes in response to the drought–rehydration process, indicating that they play a vital role in the sugar transport process regulated by drought tolerance in Poa pratensis. AtSWEET1 of Arabidopsis has been proven to be able to transport glucose [43]. PpSWEET1b, as a homologous protein of SWEET1, was significantly up-regulated under drought stress, indicating that it may improve the glucose transport capacity of Poa pratensis. In soybean, drought stress significantly increased the expression level of GmSWEET6 and GmSWEET15 in the leaves and roots. In this study, the transcription levels of multiple genes in the leaves and roots of the two materials were induced to express by drought stress, such as PpSWEET6a, -12, and -15, which were consistent with previous research results, indicating that under drought stress, the sucrose loading capacity in the leaves and sucrose unloading capacity in the roots might be enhanced. We know that the leaves transport the carbon source needed for root growth and metabolism. Therefore, strengthening the sucrose transport from leaves to roots is conducive to maintaining root growth under water deficit conditions. Moreover, the expression level of AtSWEET15 in Arabidopsis was induced during natural leaf senescence and various stresses. Chandran [44] proposed that AtSWEET15 may participate in the regulation of cell vitality to cope with osmotic stress. Thus, we speculate that the up-regulated expression of PpSWEET15 in Poa pratensis under drought stress may have the same regulatory mechanism as Arabidopsis. In addition, AtSWEET17, as a bidirectional vacuolar fructose transport protein, is proven to play a role in transporting fructose under low-temperature stress to maintain the balance of fructose in the cytoplasm of leaves and roots in Arabidopsis, thus improving the cold tolerance of plants [44]. In this study, the transcriptional level of PpSWEET17 in the leaves of two Kentucky bluegrasses was unaffected by drought stress, which indicates the different mechanisms of SWEET17 in regulating plant drought resistance and cold tolerance, and that PpSWEET17 plays a smaller role in regulating to resist drought stress in Poa pratensis.
The EBYVW4000 strain, a yeast hexose transporter deletion mutant, has been widely used to verify the complementary absorption function of yeast towards sugar substrates. Yuan et al. [45] identified 11 OsSWEETs genes as sugar transport substrates in the yeast expression system using the EBYVW4000 strain, and found that 4 of them had the ability to transport galactose. In this study, PpSWEET1a, -12, and -15 all grew slowly on a medium containing galactose, but there was no significant difference compared with the control. PpSWEET1b could resume growth on the medium containing glucose, indicating that the PpSWEET1b protein also had glucose transport activity. In addition, PpSWEET1b could also restore the growth of EBYVW4000 yeast mutant strain on the medium supplemented with sucrose and fructose. Due to the ability of the EBYVW4000 strain to hydrolyze sucrose into glucose and fructose through the secretion of invertase, it cannot be determined whether it has a direct transport effect on sucrose. Based on the previous results of subcellular localization of PpSWEET1b, it is speculated that PpSWEET1b in bluegrass may mediate the dynamic balance of sucrose, fructose, and glucose in vacuoles, and may play a role in cell osmotic balance, signal transduction, and plant stress resistance. However, neither PpSWEET12 nor PpSWEET15 detected absorption and transport activity of sucrose, fructose, glucose, and mannose in the yeast expression system. Research on OsSWEET11/14 of rice has found that it can transport sucrose and glucose in animal cell lines and oocytes, but cannot be transported in the yeast expression system [30]. Therefore, the results of sugar transport using different heterologous expression systems vary. Further research is needed to prove the transport properties of PpSWEET12 and PpSWEET15.

5. Conclusions

In summary, drought stress can promote the sucrose metabolism cycle of Kentucky bluegrass, induce sucrose accumulation in the leaves and roots, and affect the distribution and transportation of soluble sugar content in plants. Under normal conditions, the higher trehalose content in the leaves of ‘10-202’ and the higher levels of fructose and glucose are accumulated by the roots under drought stress, which causes it to better maintain the balance of osmotic potential and redox level in vivo, giving it strong drought resistance. Meanwhile, the increase in sucrose accumulation and decomposition efficiency in the leaves under drought stress is conducive to enhancing the drought resistance of plants. PpSWEET1b, -12, and -15 play an important role in the sugar transport process of drought resistance in the seedling stage of Poa pratensis, and PpSWEET1b has the activity of transporting glucose and can restore the growth of yeast mutants on sucrose and fructose medium, indicating that PpSWEET1b can coordinate the accumulation and distribution of various soluble sugars in plants, providing sufficient energy and material basis for plant growth under stress to adapt to adversity. Taken together, our findings might serve as a useful resource for investigations of the specific functions of these drought-responsive genes in the future.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/agronomy15020320/s1, Table S1: Primers for qRT-PCR; Table S2: The full-length coding sequence of PpSWEET1b, -12, and -15 in Kentucky bluegrass; Table S3: PpSWEETs gene In-Fusion clone primers combine to yeast expression vector.

Author Contributions

J.Y.: Writing—original draft, data curation. R.Z.: Data curation, methodology, writing—review and editing, funding acquisition. X.L.: Supervision, writing—review and editing, funding acquisition. D.D.: Data curation, methodology. S.W.: Methodology, visualization. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Fundamental Research Funds of Chinese Academy of Forestry (project # CAFYBB2022XA002).

Data Availability Statement

The original contributions presented in the study are included in the article/Supplementary Materials, and further inquiries can be directed to the corresponding authors.

Acknowledgments

Thank you to Eckhard Boles from Germany and Wu Binghua from Fujian Agricultural and Forestry University for presenting the yeast strain EBYVW4000.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References

  1. Li, L.; Sheen, J. Dynamic and diverse sugar signaling. Curr. Opin. Plant Biol. 2016, 33, 116–125. [Google Scholar] [CrossRef] [PubMed]
  2. Hennion, N.; Durand, M.; Vriet, C.; Doidy, J.; Maurousset, L.; Lemoine, R.; Pourtau, N. Sugars en route to the roots. transport, metabolism and storage within plant roots and towards microorganisms of the rhizosphere. Physiol. Plantarum. 2019, 165, 44–57. [Google Scholar] [CrossRef]
  3. Salmon, Y.; Lintunen, A.; Dayet, A.; Chan, T.; Dewar, R.; Vesala, T.; Holtta, T. Leaf carbon and water status control stomatal and nonstomatal limitations of photosynthesis in trees. New Phytol. 2020, 226, 690–703. [Google Scholar] [CrossRef] [PubMed]
  4. Hu, M.Y.; Shi, Z.G.; Zhang, Z.B.; Zhang, Y.J.; Li, H. Effects of exogenous glucose on seed germination and antioxidant capacity in wheat seedlings under salt stress. Plant Growth Regul. 2012, 68, 177–188. [Google Scholar] [CrossRef]
  5. Ahmad, I.Z. Role of sugars in abiotic stress signaling in plants. In Plant Signaling Molecules; Khan, M.I.R., Reddy, P.S., Ferrante, A., Khan, N.A., Eds.; Woodhead Publishing: Sawston, UK; Elsevier: Amsterdam, The Netherlands, 2019; pp. 207–217. [Google Scholar] [CrossRef]
  6. Slama, I.; Abdelly, C.; Bouchereau, A.; Flowers, T.; Savoure, A. Diversity, distribution and roles of osmoprotective compounds accumulated in halophytes under abiotic stress. Ann. Bot.-Lond. 2015, 115, 433–447. [Google Scholar] [CrossRef]
  7. Ayako, N.Y.; Yukinori, Y.; Shigeru, S. The contribution of carbohydrates including raffinose family oligosaccharides and sugar alcohols to protection of plant cells from oxidative damage. Plant Signal 2008, 3, 1016–1018. [Google Scholar] [CrossRef]
  8. Hoermiller, I.I.; Naegele, T.; Augustin, H.; Stutz, S.; Weckwerth, W.; Heyer, A.G. Subcellular reprogramming of metabolism during cold acclimation in Arabidopsis thaliana. Plant Physiol. 2017, 40, 602–610. [Google Scholar] [CrossRef] [PubMed]
  9. Sharma, S.; Sreenivasulu, N.; Harshavardhan, V.T.; Seiler, C.; Sharma, S.; Khalil, Z.N.; Akhunov, E.; Sehgal, S.K.; Roeder, M.S. Delineating the structural, functional and evolutionary relationships of sucrose phosphate synthase gene family II in wheat and related grasses. BMC Plant Biol. 2010, 10, 134. [Google Scholar] [CrossRef] [PubMed]
  10. Turhan, E.; Ergin, S. Soluble sugars and sucrose-metabolizing enzymes related to cold acclimation of sweet cherry cultivars grafted on different rootstocks. Sci. World J. 2012, 2012, 979682. [Google Scholar] [CrossRef] [PubMed]
  11. Roitsch, T.; Balibrea, M.E.; Hofmann, M.; Proels, R.; Sinha, A.K. Extracellular invertase: Key metabolic enzyme and PR protein. J. Exp. Bot. 2003, 54, 513–524. [Google Scholar] [CrossRef]
  12. Zulfiqar, F.; Akram, N.A.; Ashraf, M. Osmoprotection in plants under abiotic stresses: New insights into a classical phenomenon. Planta 2020, 251, 3. [Google Scholar] [CrossRef]
  13. Iordachescu, M.; Imai, R. Trehalose biosynthesis in response to abiotic stresses. J. Integr. Plant Biol. 2009, 50, 1223–1229. [Google Scholar] [CrossRef]
  14. Ainsworth, E.A.; Bush, D.R. Carbohydrate export from the leaf: A highly regulated process and target to enhance photosynthesis and productivity. Plant Physiol. 2011, 155, 64–69. [Google Scholar] [CrossRef] [PubMed]
  15. Chen, L.Q.; Qu, X.Q.; Hou, B.H.; Sosso, D.; Osorio, S.; Fernie, A.R.; Frommer, W.B. Sucrose efflux mediated by SWEET proteins as a key step for phloem transport. Science 2012, 335, 207–211. [Google Scholar] [CrossRef]
  16. Jeena, G.S.; Kumar, S.; Shukla, R.K. Structure, evolution and diverse physiological roles of sweet sugar transporters in plants. Plant Mol. Biol. 2019, 100, 351–365. [Google Scholar] [CrossRef]
  17. Yue, C.; Cao, H.L.; Wang, L.; Zhou, Y.H.; Huang, Y.T.; Hao, X.Y.; Wang, C.; Wang, B.; Yang, Y.J.; Wang, X.C. Effects of cold acclimation on sugar metabolism and sugar-related gene expression in tea plant during the winter season. Plant Mol. Biol. 2015, 88, 591–608. [Google Scholar] [CrossRef] [PubMed]
  18. Feng, C.Y.; Han, J.X.; Han, X.X.; Jiang, J. Genome-wide identification, phylogeny, and expression analysis of the SWEET gene family in tomato. Gene 2015, 573, 261–272. [Google Scholar] [CrossRef] [PubMed]
  19. Guo, W.J.; Nagy, R.; Chen, H.Y.; Pfrunder, S.; Yu, Y.C.; Santelia, D.; Frommer, W.B.; Martinoia, E. SWEET17, a facilitative transporter, mediates fructose transport across the tonoplast of Arabidopsis roots and leaves. Plant Physiol. 2014, 164, 777–789. [Google Scholar] [CrossRef] [PubMed]
  20. Zhang, R.; Li, J.J.; Wang, M.; Ji, L.H.; Hou, X.; Ma, X.; Ma, H.L. Physiological responses to drought stress in 11 different kentucky bluegrass germplasm and the evaluation of their drought tolerance. Grassl. Turf 2021, 41, 113–121. [Google Scholar] [CrossRef]
  21. Zhang, R.; Niu, K.J.; Ma, H.L. Identification and expression analysis of the SWEET gene family from Poa pratensis under abiotic stresses. DNA Cell Biol. 2020, 39, 1606–1620. [Google Scholar] [CrossRef]
  22. Xu, W.; Cui, K.H.; Xu, A.H.; Nie, L.X.; Huang, J.L.; Peng, S.B. Drought stress condition increases root to shoot ratio via alteration of carbohydrate partitioning and enzymatic activity in rice seedlings. Acta Physiol. Plant 2015, 37, 9. [Google Scholar] [CrossRef]
  23. Niu, K.J. The Role of 5-Aminolevulinic Acid on Regulation Mechanism of Photosynthesis in Kentucky Bluegrass Seedlings Under Drought Stress; Gansu Agricultural University: Lanzhou, China, 2018; Available online: https://kns-cnki-net-443.webvpn.las.ac.cn/kns8s/defaultresult/index?crossids=YSTT4HG0%2CLSTPFY1C%2CJUP3MUPD%2CMPMFIG1A%2CWQ0UVIAA%2CBLZOG7CK%2CPWFIRAGL%2CEMRPGLPA%2CNLBO1Z6R%2CNN3FJMUV&korder=SU&kw=The+Role+of+5-Aminolevulinic+Acid+on+Regulation+Mechanism+of+Photosynthesis+in+Kentucky+Bluegrass+Se (accessed on 20 January 2025).
  24. Li, Y.P. Determination of fructose, glucose and sucrose in tea by high performance liquid chromatography-differential refraction detector. Guangdong Chem. Ind. 2016, 43, 187–188. [Google Scholar]
  25. Kuai, J.; Liu, Z.; Wang, Y.; Meng, Y.; Chen, B.; Zhao, W.; Zhou, Z.; Oosterhuis, D.M. Waterlogging during flowering and boll forming stages affects sucrose metabolism in the leaves subtending the cotton boll and its relationship with boll weight. Plant Sci. 2014, 223, 79–98. [Google Scholar] [CrossRef] [PubMed]
  26. Zhang, R.; Jia, Z.F.; Ma, X.; Ma, H.L.; Zhao, Y.W. Characterising the morphological characters and carbohydrate metabolism of oat culms and their association with lodging resistance. Plant Biol. 2020, 22, 267–276. [Google Scholar] [CrossRef]
  27. Niu, K.J.; Shi, Y.; Ma, H.L. Selection of candidate reference genes for gene expression analysis in Kentucky bluegrass (Poa pratensis L.) under abiotic stress. Front. Plant Sci. 2017, 8, 193. [Google Scholar] [CrossRef]
  28. Fuhrmeister, R.; Streubel, J. Functional Analysis of Plant Monosaccharide Transporters Using a Simple Growth Complementation Assay in Yeast. Bio-Protocol 2023, 13, e4733. [Google Scholar] [CrossRef]
  29. Niu, K.J.; Ma, X.; Liang, G.L.; Ma, H.L.; Jia, Z.F.; Liu, W.H.; Yu, Q.Q. 5-Aminolevulinic acid modulates antioxidant defense systems and miti-gates drought-induced damage in Kentucky bluegrass seedlings. Protoplasma 2017, 254, 2083–2094. [Google Scholar] [CrossRef] [PubMed]
  30. Muller, B.; Pantin, F.; Gnard, M.; Turc, O.; Freixes, S.; Piques, M.; Gibon, Y. Water deficits uncouple growth from photosynthesis, increase C content, and modify the relationships between C and growth in sink organs. J. Exp. Bot. 2011, 62, 1715–1729. [Google Scholar] [CrossRef] [PubMed]
  31. Du, Y.L.; Zhao, Q.; Chen, L.R.; Yao, X.D.; Zhang, W.; Zhang, B.; Xie, F.T. Effect of drought stress on sugar metabolism in leaves and roots of soybean seedlings. Plant Physiol. Bioch. 2020, 146, 1–12. [Google Scholar] [CrossRef]
  32. Cuellar-Ortiz, S.M.; Arrieta-Montiel, M.D.; Acosta-Gallegos, J.; Covarrubias, A.A. Relationship between carbohydrate partitioning and drought resistance in common bean. Plant Cell Environ. 2008, 31, 1399–1409. [Google Scholar] [CrossRef]
  33. Asensi-Fabado, M.A.; Ammon, A.; Sonnewald, U.; Munne-Bosch, S.; Voll, L.M. Tocopherol deficiency reduces sucrose export from salt-stressed potato leaves independently of oxidative stress and symplastic obstruction by callose. J. Exp. Bot. 2015, 66, 957–971. [Google Scholar] [CrossRef]
  34. Chen, L.Q.; Hou, B.H.; Lalonde, S.; Takanaga, H.; Hartung, M.L.; Qu, X.Q.; Guo, W.J.; Kim, J.G.; Underwood, W.; Chaudhuri, B.; et al. Sugar transporters for intercellular exchange and nutrition of pathogens. Nature 2010, 468, 527–532. [Google Scholar] [CrossRef]
  35. Valerio, C.; Costa, A.; Marri, L.; Issakidis-Bourguet, E.; Pupillo, P.; Trost, P.; Sparla, F. Thioredoxin-regulated β-amylase (BAM1) triggers diurnal starch degradation in guard cells, and in mesophyll cells under osmotic stress. J. Exp. Bot. 2010, 62, 545–555. [Google Scholar] [CrossRef] [PubMed]
  36. Zanella, M.; Borghi, G.L.; Pirone, C.; Thalmann, M.; Pazmino, D.; Costa, A.; Santelia, D.; Trost, P.; Sparla, F. β-amylase 1 (BAM1) degrades transitory starch to sustain proline biosynthesis during drought stress. J. Exp. Bot. 2016, 67, 1819–1826. [Google Scholar] [CrossRef] [PubMed]
  37. Lu, Y.; Sharkey, T.D. The importance of maltose in transitory starch breakdown. Plant Cell Environ. 2006, 29, 353–366. [Google Scholar] [CrossRef] [PubMed]
  38. Kaplan, F.; Guy, C.L. β-amylase induction and the protective role of maltose during temperature shock. Plant Physiol. 2004, 135, 1674–1684. [Google Scholar] [CrossRef]
  39. Crowe, J.H. Trehalose as a “chemical chaperone”: Fact and fantasy. In Molecular Aspects of the Stress Response: Chaperones, Membranes and Networks; Csermely, P., Vigh, L., Eds.; Springer: Cham, Switzerland, 2007. [Google Scholar] [CrossRef]
  40. Zhang, Q.W.; Song, X.M.; Bartels, D. Sugar metabolism in the desiccation tolerant grass Oropetium thomaeum in response to environmental stresses. Plant Sci. 2018, 270, 30–36. [Google Scholar] [CrossRef]
  41. Zhang, X.B.; Lei, L.; Lai, J.S.; Zhao, H.M.; Song, W.B. Effects of drought stress and water recovery on physiological responses and gene expression in maize seedlings. BMC Plant Biol. 2018, 18, 68. [Google Scholar] [CrossRef] [PubMed]
  42. Hu, B.; Wu, H.; Huang, W.F.; Song, J.B.; Zhou, Y.; Lin, Y.J. SWEET gene family in Medicago truncatula: Genome-wide identification, expression and substrate specificity analysis. Plants 2019, 8, 338. [Google Scholar] [CrossRef]
  43. Xuan, Y.H.; Hu, Y.B.; Chen, L.Q.; Sosso, D.; Ducat, D.C.; Hou, B.H.; Frommer, W.B. Functional role of oligomerization for bacterial and plant SWEET sugar transporter family. Proc. Natl. Acad. Sci. USA 2013, 110, E3685–E3694. [Google Scholar] [CrossRef]
  44. Chandran, D. Co-Option of developmentally regulated plant SWEET transporters for pathogen nutrition and abiotic stress tolerance. IUBMB Life 2015, 67, 461–471. [Google Scholar] [CrossRef]
  45. Yuan, M.; Zhao, J.; Huang, R.; Li, X.; Xiao, J.; Wang, S. Rice MtN3/saliva/SWEET gene family: Evolution, expression profiling, and sugar transport. J. Integr. Plant Biol. 2014, 56, 559–570. [Google Scholar] [CrossRef] [PubMed]
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Figure 1. Effects of drought–rehydration on the contents of fructose (a,b), glucose (c,d), sucrose (e,f), maltose (g,h), and trehalose (i,j) in the leaves and roots of Kentucky bluegrass. BM-CK means control of ‘Blue moon’; BM-T means drought–rehydration treatment of ‘Blue moon’; 10-202-CK means control of ‘10-202’; 10-202-T means drought–rehydration treatment of ‘10-202’. Data show the means ± standard deviation of three biological and technology replicates. The significant differences between the control and drought-treated plants are based on Student’s t-tests at different time points. * p < 0.05, ** p < 0.01.
Figure 1. Effects of drought–rehydration on the contents of fructose (a,b), glucose (c,d), sucrose (e,f), maltose (g,h), and trehalose (i,j) in the leaves and roots of Kentucky bluegrass. BM-CK means control of ‘Blue moon’; BM-T means drought–rehydration treatment of ‘Blue moon’; 10-202-CK means control of ‘10-202’; 10-202-T means drought–rehydration treatment of ‘10-202’. Data show the means ± standard deviation of three biological and technology replicates. The significant differences between the control and drought-treated plants are based on Student’s t-tests at different time points. * p < 0.05, ** p < 0.01.
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Figure 2. Effects of drought–rehydration on the contents of starch. * p < 0.05, ** p < 0.01.
Figure 2. Effects of drought–rehydration on the contents of starch. * p < 0.05, ** p < 0.01.
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Figure 3. Effects of drought–rehydration on the activities of SPS (a,b), SS (c,d), S-AI (e,f), and N/A-Inv (g,h) in the leaves and roots of Kentucky bluegrass. BM-CK means control of ‘Blue moon’; BM-T means drought–rehydration treatment of ‘Blue moon’; 10-202-CK means control of ‘10-202’; 10-202-T means drought–rehydration treatment of ‘10-202’. Data show the means ± standard deviation of three biological and technology replicates. The significant differences between the control and drought-treated plants are based on Student’s t-tests at different time points. * p < 0.05, ** p < 0.01.
Figure 3. Effects of drought–rehydration on the activities of SPS (a,b), SS (c,d), S-AI (e,f), and N/A-Inv (g,h) in the leaves and roots of Kentucky bluegrass. BM-CK means control of ‘Blue moon’; BM-T means drought–rehydration treatment of ‘Blue moon’; 10-202-CK means control of ‘10-202’; 10-202-T means drought–rehydration treatment of ‘10-202’. Data show the means ± standard deviation of three biological and technology replicates. The significant differences between the control and drought-treated plants are based on Student’s t-tests at different time points. * p < 0.05, ** p < 0.01.
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Figure 4. Effects of drought–rehydration on the expression of PpSPS (a,b), PpSS (c,d), PpS-AI (e,f), PpCWINV (g,h), and PpN/A-Inv (i,j) in the leaves and roots of Kentucky bluegrass. BM-CK means control of ‘Blue moon’; BM-T means drought–rehydration treatment of ‘Blue moon’; 10-202-CK means control of ‘10-202’; 10-202-T means drought–rehydration treatment of ‘10-202’. Data show the means ± standard deviation of three biological and technology replicates. The significant differences between the control and drought-treated plants are based on Student’s t-tests at different time points. * p < 0.05, ** p < 0.01.
Figure 4. Effects of drought–rehydration on the expression of PpSPS (a,b), PpSS (c,d), PpS-AI (e,f), PpCWINV (g,h), and PpN/A-Inv (i,j) in the leaves and roots of Kentucky bluegrass. BM-CK means control of ‘Blue moon’; BM-T means drought–rehydration treatment of ‘Blue moon’; 10-202-CK means control of ‘10-202’; 10-202-T means drought–rehydration treatment of ‘10-202’. Data show the means ± standard deviation of three biological and technology replicates. The significant differences between the control and drought-treated plants are based on Student’s t-tests at different time points. * p < 0.05, ** p < 0.01.
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Figure 5. Expression patterns of PpSWEETs in the leaves and roots of ‘Blue moon’ (a) and ‘10-202’ (b) under drought–rehydration treatment. Log2 FC represents log2 fold change.
Figure 5. Expression patterns of PpSWEETs in the leaves and roots of ‘Blue moon’ (a) and ‘10-202’ (b) under drought–rehydration treatment. Log2 FC represents log2 fold change.
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Figure 6. Growth of pDRTXa-PpSWEETs yeast transformed cells on different sugar substrate culture media. Four columns in each group represent different bacterial fluid gradients from left to right, which are 1, 0.1, 0.01, and 0.001, respectively.
Figure 6. Growth of pDRTXa-PpSWEETs yeast transformed cells on different sugar substrate culture media. Four columns in each group represent different bacterial fluid gradients from left to right, which are 1, 0.1, 0.01, and 0.001, respectively.
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Table 1. The peak time, regression equation, and correlation coefficient.
Table 1. The peak time, regression equation, and correlation coefficient.
SugarThe Peak Time (min)Regression EquationCorrelation Coefficient
fructose6.977Y = 153131X + 6412.40.9941
glucose8.073Y = 244296X + 1171.90.9965
sucrose10.758Y = 186365X − 6125.60.9952
maltose12.353Y = 141191X + 1959.70.9967
trehalose13.309Y = 176065X + 2595.70.9946
Table 2. Effect of drought–rewatering treatment on the content of RWC and EL of leaves.
Table 2. Effect of drought–rewatering treatment on the content of RWC and EL of leaves.
IndicatorsTreatment6 d12 dR1 dR5 d
RWCBM-CK0.93 ± 0.016 a0.93 ± 0.013 a0.86 ± 0.011 a0.88 ± 0.04 ab
BM-T0.80 ± 0.015 b0.31 ± 0.013 c0.72 ± 0.013 b0.81 ± 0.01 b
10-202-CK0.89 ± 0.008 a0.88 ± 0.039 a0.86 ± 0.001 a0.89 ± 0.015 a
10-202-T0.88 ± 0.027 a0.52 ± 0.023 b0.70 ± 0.039 b0.82 ± 0.005 ab
ELBM-CK0.08 ± 0.005 c0.08 ± 0.004 c0.07 ± 0.002 d0.09 ± 0.002 c
BM-T0.17 ± 0.004 a0.29 ± 0.017 a0.18 ± 0.01 a0.12 ± 0.005 a
10-202-CK0.09 ± 0.006 c0.09 ± 0.008 c0.09 ± 0.007 c0.09 ± 0.003 c
10-202-T0.13 ± 0.004 b0.18 ± 0.006 b0.15 ± 0.005 b0.10 ± 0.001 b
Different lowercase letters in the table represent significant difference at the 0.05 level. BM-CK: control of ‘Blue moon’; BM-T: drought–rehydration treatment of ‘Blue moon’; 10-202-CK: control of ‘10-202’; 10-202-T: drought–rehydration treatment of ‘10-202’. This is the same as below.
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Yu, J.; Zhang, R.; Li, X.; Dong, D.; Wang, S. Sugar Metabolism and Transport in Response to Drought–Rehydration in Poa pratensis. Agronomy 2025, 15, 320. https://doi.org/10.3390/agronomy15020320

AMA Style

Yu J, Zhang R, Li X, Dong D, Wang S. Sugar Metabolism and Transport in Response to Drought–Rehydration in Poa pratensis. Agronomy. 2025; 15(2):320. https://doi.org/10.3390/agronomy15020320

Chicago/Turabian Style

Yu, Jiangdi, Ran Zhang, Xiaoxia Li, Di Dong, and Sining Wang. 2025. "Sugar Metabolism and Transport in Response to Drought–Rehydration in Poa pratensis" Agronomy 15, no. 2: 320. https://doi.org/10.3390/agronomy15020320

APA Style

Yu, J., Zhang, R., Li, X., Dong, D., & Wang, S. (2025). Sugar Metabolism and Transport in Response to Drought–Rehydration in Poa pratensis. Agronomy, 15(2), 320. https://doi.org/10.3390/agronomy15020320

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