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Salinity Stress in Plants and Molecular Responses
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Salinity Stress in Plants and Molecular Responses

A special issue of Plants (ISSN 2223-7747). This special issue belongs to the section "Plant Physiology and Metabolism".

Deadline for manuscript submissions: closed (31 March 2021) | Viewed by 71447

Special Issue Editors

Dr. Pasqualina Woodrow

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Guest Editor
Department of Environmental Biological and Pharmaceutical Sciences and Technologies. University of Campania "Luigi Vanvitelli", Via Antonio Vivaldi, 43-81100 Caserta, Italy
Interests: genetics and plant molecular physiology; plant molecular characterization by mitochondrial and nuclear genes; effect of abiotic stresses on retrotransposon mobilization; gene stress activation; plant–fungi interactions and gene resistance
Special Issues, Collections and Topics in MDPI journals
Dr. Loredana Filomena Ciarmiello

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Guest Editor
Department of Environmental Biological and Pharmaceutical Sciences and Technologies, University of Campania "Luigi Vanvitelli", Via Antonio Vivaldi, 43-81100 Caserta, Italy
Interests: genetics and plant molecular physiology; application of molecular markersfor genotipic characterization and plant improvement; effect of abiotic stresses on retrotransposon mobilization; gene stress activation
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Salinity is a major environmental stressor for plants and results in significant economic losses worldwide. Salinity influences different plant developmental stages including germination, shoot and root lengths, leaf area, plant height, and flower development. Plants, being sessile organisms, are unable to escape unfavorable environmental conditions, and therefore, have evolved with a wide range of response mechanisms that allow plants to adapt to adverse environmental conditions, including the expression of stress protective proteins. Adaptive transcriptional and translation changes ensure that a strong defence response occurs under high salinity conditions. To develop the resistance of cultivated plants to salt stress, it is therefore important to isolate, identify, and study the functions of new genes related to tolerance.

Dr. Loredana Filomena Ciarmiello
Dr. Pasqualina Woodrow
Guest Editors

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Keywords

  • gene activation
  • salt stress adaptive responses
  • salt tolerance QTLs
  • retrotransposons activation

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Published Papers (18 papers)

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Research

16 pages, 1886 KiB  
Article
Genetic Diversity and Synergistic Modulation of Salinity Tolerance Genes in Aegilops tauschii Coss
by Adeel Abbas, Haiyan Yu, Hailan Cui and Xiangju Li
Plants 2021, 10(7), 1393; https://doi.org/10.3390/plants10071393 - 7 Jul 2021
Cited by 8 | Viewed by 2468
Abstract
Aegilops tauschii Coss. (2n = 2x = 14, DD) is a problematic weed and a rich source of genetic material for wheat crop improvement programs. We used physiological traits (plant height, dry weight biomass, Na+ and K+ concentration) and 14 microsatellite [...] Read more.
Aegilops tauschii Coss. (2n = 2x = 14, DD) is a problematic weed and a rich source of genetic material for wheat crop improvement programs. We used physiological traits (plant height, dry weight biomass, Na+ and K+ concentration) and 14 microsatellite markers to evaluate the genetic diversity and salinity tolerance in 40 Ae. tauschii populations. The molecular marker allied with salinity stress showed polymorphisms, and a cluster analysis divided the populations into different groups, which indicated diversity among populations. Results showed that the expression level of AeHKT1;4 and AeNHX1 were significantly induced during salinity stress treatments (50 and 200 mM), while AeHKT1;4 showed relative expression in roots, and AeNHX1 was expressed in leaves under the control conditions. Compared with the control conditions, the expression level of AeHKT1;4 significantly increased 1.7-fold under 50 mM salinity stress and 4.7-fold under 200 mM salinity stress in the roots of Ae. tauschii. AeNHX1 showed a relative expression level of 1.6-fold under 50 mM salinity stress and 4.6-fold under 200 mM salinity stress compared with the control conditions. The results provide strong evidence that, under salinity stress conditions, AeHKT1;4 and AeNHX1 synergistically regulate the Na+ homeostasis through regulating Na+ transport in Ae. tauschii. AeNHX1 sequestrated the Na+ into vacuoles, which control the regulation of Na+ transport from roots to leaves under salinity stress conditions in Ae. tauschii. Full article
(This article belongs to the Special Issue Salinity Stress in Plants and Molecular Responses)
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14 pages, 1467 KiB  
Article
Salinity Stress Affects Photosynthesis, Malondialdehyde Formation, and Proline Content in Portulaca oleracea L.
by Helena Hnilickova, Kamil Kraus, Pavla Vachova and Frantisek Hnilicka
Plants 2021, 10(5), 845; https://doi.org/10.3390/plants10050845 - 22 Apr 2021
Cited by 150 | Viewed by 8052
Abstract
In this investigation, the effect of salt stress on Portulaca oleracea L. was monitored at salinity levels of 100 and 300 mM NaCl. At a concentration of 100 mM NaCl there was a decrease in stomatal conductance (gs) simultaneously with an increase in [...] Read more.
In this investigation, the effect of salt stress on Portulaca oleracea L. was monitored at salinity levels of 100 and 300 mM NaCl. At a concentration of 100 mM NaCl there was a decrease in stomatal conductance (gs) simultaneously with an increase in CO2 assimilation (A) at the beginning of salt exposure (day 3). However, the leaf water potential (ψw), the substomatal concentration of CO2 (Ci), the maximum quantum yield of photosystem II (Fv/Fm), and the proline and malondialdehyde (MDA) content remained unchanged. Exposure to 300 mM NaCl caused a decrease in gs from day 3 and a decrease in water potential, CO2 assimilation, and Fv/Fm from day 9. There was a large increase in proline content and a significantly higher MDA concentration on days 6 and 9 of salt stress compared to the control group. After 22 days of exposure to 300 mM NaCl, there was a transition from the C4 cycle to crassulacean acid metabolism (CAM), manifested by a rapid increase in substomatal CO2 concentration and negative CO2 assimilation values. These results document the tolerance of P. oleracea to a lower level of salt stress and the possibility of its use in saline localities. Full article
(This article belongs to the Special Issue Salinity Stress in Plants and Molecular Responses)
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13 pages, 2630 KiB  
Article
Salinity Effect on Germination and Further Development of Parasitic Cuscuta spp. and Related Non-Parasitic Vines
by Lyuben Zagorchev, Alexandra Atanasova, Kalina Pachedjieva, Anita Tosheva, Junmin Li and Denitsa Teofanova
Plants 2021, 10(3), 438; https://doi.org/10.3390/plants10030438 - 25 Feb 2021
Cited by 2 | Viewed by 2876
Abstract
Plants are continuously subjected to the unfavorable impact of abiotic stress factors, of which soil salinity is among the most adverse. Although away from direct soil contact throughout most of their lifecycle, stem parasitic plants of the genus Cuscuta, family Convolvulaceae are [...] Read more.
Plants are continuously subjected to the unfavorable impact of abiotic stress factors, of which soil salinity is among the most adverse. Although away from direct soil contact throughout most of their lifecycle, stem parasitic plants of the genus Cuscuta, family Convolvulaceae are also affected by salinity. The present study aimed to assess salt stress impact on germination and early establishment of three Cuscuta species, in comparison to related nonparasitic vines of the same family. It was found, that Cuscuta spp. are highly sensitive to NaCl concentration within the range of 200 mM. Germination was delayed in time and reduced by nearly 70%, accompanied by decrease in further seedling growth, ability to infect host plants and growth rate of established parasites. The nonparasitic vines showed similar sensitivity to salinity at germination level, but appeared to adapt better after the stress factor was removed. However, the negative effect of salinity did not fully prevent some of the Cuscuta species from infecting hosts, probably a beneficial characteristic at a species level, allowing the parasite to successfully thrive under the scarce host availability under saline conditions. Full article
(This article belongs to the Special Issue Salinity Stress in Plants and Molecular Responses)
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23 pages, 2840 KiB  
Article
Impact of Foliar Application of Chitosan Dissolved in Different Organic Acids on Isozymes, Protein Patterns and Physio-Biochemical Characteristics of Tomato Grown under Salinity Stress
by Mohamed S. Attia, Mahmoud S. Osman, Amr S. Mohamed, Hany A. Mahgoub, Mohamed O. Garada, Eslam S. Abdelmouty and Arafat Abdel Hamed Abdel Latef
Plants 2021, 10(2), 388; https://doi.org/10.3390/plants10020388 - 18 Feb 2021
Cited by 55 | Viewed by 5887
Abstract
In this study, the anti-stress capabilities of the foliar application of chitosan, dissolved in four different organic acids (acetic acid, ascorbic acid, citric acid and malic acid) have been investigated on tomato (Solanum lycopersicum L.) plants under salinity stress (100 mM NaCl). [...] Read more.
In this study, the anti-stress capabilities of the foliar application of chitosan, dissolved in four different organic acids (acetic acid, ascorbic acid, citric acid and malic acid) have been investigated on tomato (Solanum lycopersicum L.) plants under salinity stress (100 mM NaCl). Morphological traits, photosynthetic pigments, osmolytes, secondary metabolites, oxidative stress, minerals, antioxidant enzymes activity, isozymes and protein patterns were tested for potential tolerance of tomato plants growing under salinity stress. Salinity stress was caused a reduction in growth parameters, photosynthetic pigments, soluble sugars, soluble proteins and potassium (K+) content. However, the contents of proline, ascorbic acid, total phenol, malondialdehyde (MDA), hydrogen peroxide (H2O2), sodium (Na+) and antioxidant enzyme activity were increased in tomato plants grown under saline conditions. Chitosan treatments in any of the non-stressed plants showed improvements in morphological traits, photosynthetic pigments, osmolytes, total phenol and antioxidant enzymes activity. Besides, the harmful impacts of salinity on tomato plants have also been reduced by lowering MDA, H2O2 and Na+ levels. Chitosan treatments in either non-stressed or stressed plants showed different responses in number and density of peroxidase (POD), polyphenol oxidase (PPO) and superoxide dismutase (SOD) isozymes. NaCl stress led to the diminishing of protein bands with different molecular weights, while they were produced again in response to chitosan foliar application. These responses were varied according to the type of solvent acid. It could be suggested that foliar application of chitosan, especially that dissolved in ascorbic or citric acid, could be commercially used for the stimulation of tomato plants grown under salinity stress. Full article
(This article belongs to the Special Issue Salinity Stress in Plants and Molecular Responses)
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14 pages, 2569 KiB  
Article
Application of Exogenous Protectants Mitigates Salt-Induced Na+ Toxicity and Sustains Cotton (Gossypium hirsutum L.) Seedling Growth: Comparison of Glycine Betaine and Salicylic Acid
by Abdoul Kader Mounkaila Hamani, Jinsai Chen, Mukesh Kumar Soothar, Guangshuai Wang, Xiaojun Shen, Yang Gao and Ranjian Qiu
Plants 2021, 10(2), 380; https://doi.org/10.3390/plants10020380 - 17 Feb 2021
Cited by 18 | Viewed by 2723
Abstract
Soil salinization adversely affects agricultural productivity. Mitigating the adverse effects of salinity represents a current major challenge for agricultural researchers worldwide. The effects of exogenously applied glycine betaine (GB) and salicylic acid (SA) on mitigating sodium toxicity and improving the growth of cotton [...] Read more.
Soil salinization adversely affects agricultural productivity. Mitigating the adverse effects of salinity represents a current major challenge for agricultural researchers worldwide. The effects of exogenously applied glycine betaine (GB) and salicylic acid (SA) on mitigating sodium toxicity and improving the growth of cotton seedlings subjected to salt stress remain unclear. The treatments in a phytotron included a control (CK, exogenously untreated, non-saline), two NaCl conditions (0 and 150 mM), four exogenous GB concentrations (0, 2.5, 5.0, and 7.5 mM), and four exogenous SA concentrations (0, 1.0, 1.5, and 2.0 mM). The shoot and roots exposed to 150 mM NaCl without supplementation had significantly higher Na+ and reduced K+, Ca2+, and Mg2+ contents, along with lowered biomass, compared with those of CK. Under NaCl stress, exogenous GB and SA at all concentrations substantially inversed these trends by improving ion uptake regulation and biomass accumulation compared with NaCl stress alone. Supplementation with 5.0 mM GB and with 1.0 mM SA under NaCl stress were the most effective conditions for mitigating Na+ toxicity and enhancing biomass accumulation. NaCl stress had a negative effect on plant growth parameters, including plant height, leaf area, leaf water potential, and total nitrogen (N) in the shoot and roots, which were improved by supplementation with 5.0 mM GB or 1.0 mM SA. Supplementation with 5.0 mM exogenous GB was more effective in controlling the percentage loss of conductivity (PLC) under NaCl stress. Full article
(This article belongs to the Special Issue Salinity Stress in Plants and Molecular Responses)
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19 pages, 749 KiB  
Article
Physiological and Biochemical Responses of Ungrafted and Grafted Bell Pepper Plants (Capsicum annuum L. var. grossum (L.) Sendtn.) Grown under Moderate Salt Stress
by Nina Kacjan Maršić, Petra Štolfa, Dominik Vodnik, Katarina Košmelj, Maja Mikulič-Petkovšek, Bojka Kump, Rajko Vidrih, Doris Kokalj, Saša Piskernik, Blaz Ferjančič, Maja Dragutinović, Robert Veberič, Metka Hudina and Helena Šircelj
Plants 2021, 10(2), 314; https://doi.org/10.3390/plants10020314 - 6 Feb 2021
Cited by 12 | Viewed by 3240
Abstract
The response of grafted bell pepper plants (Capsicum annuum L. var. grossum (L.) Sendtn.) to salt stress was investigated by analyzing the photosynthetic traits and mineral content of the plants and the metabolic composition of the fruit. The bell pepper variety “Vedrana” [...] Read more.
The response of grafted bell pepper plants (Capsicum annuum L. var. grossum (L.) Sendtn.) to salt stress was investigated by analyzing the photosynthetic traits and mineral content of the plants and the metabolic composition of the fruit. The bell pepper variety “Vedrana” was grafted onto the salt-tolerant rootstock “Rocal F1” and grown at two salinities (20 mM and 40 mM NaCl) and control (0 mM NaCl) during the spring–summer period. On a physiological level, similar stomatal restriction of photosynthesis in grafted and ungrafted plants indicated that grafting did not alleviate water balance disturbances under increased salt exposure. Measurements of midday water potential did not show improved water status of grafted plants. The similar metabolic changes in grafted and ungrafted plants were also reflected in similarly reduced fruit yields. Thus, this grafting did not reduce the risk of ionic and osmotic imbalance in pepper plants grown under moderate salt treatment. Changes in the biochemical profiles of the pepper fruit were seen for both added-salt treatments. The fruit phenolic compounds were affected by rootstock mediation, although only for the July harvest, where total phenolics content increased with 40 mM NaCl treatment. Fruit ascorbic acid content increased with the duration of salt stress, without the mediation of the rootstock. The high salt dependence of this quality trait in pepper fruit appears to lead to more limited rootstock mediation effects. Full article
(This article belongs to the Special Issue Salinity Stress in Plants and Molecular Responses)
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26 pages, 3938 KiB  
Article
Use of Hyperspectral Reflectance Sensing for Assessing Growth and Chlorophyll Content of Spring Wheat Grown under Simulated Saline Field Conditions
by Salah El-Hendawy, Salah Elsayed, Nasser Al-Suhaibani, Majed Alotaibi, Muhammad Usman Tahir, Muhammad Mubushar, Ahmed Attia and Wael M. Hassan
Plants 2021, 10(1), 101; https://doi.org/10.3390/plants10010101 - 6 Jan 2021
Cited by 18 | Viewed by 3200
Abstract
The application of proximal hyperspectral sensing, using simple vegetation indices, offers an easy, fast, and non-destructive approach for assessing various plant variables related to salinity tolerance. Because most existing indices are site- and species-specific, published indices must be further validated when they are [...] Read more.
The application of proximal hyperspectral sensing, using simple vegetation indices, offers an easy, fast, and non-destructive approach for assessing various plant variables related to salinity tolerance. Because most existing indices are site- and species-specific, published indices must be further validated when they are applied to other conditions and abiotic stress. This study compared the performance of various published and newly constructed indices, which differ in algorithm forms and wavelength combinations, for remotely assessing the shoot dry weight (SDW) as well as chlorophyll a (Chla), chlorophyll b (Chlb), and chlorophyll a+b (Chlt) content of two wheat genotypes exposed to three salinity levels. Stepwise multiple linear regression (SMLR) was used to extract the most influential indices within each spectral reflectance index (SRI) type. Linear regression based on influential indices was applied to predict plant variables in distinct conditions (genotypes, salinity levels, and seasons). The results show that salinity levels, genotypes, and their interaction had significant effects (p ≤ 0.05 and 0.01) on all plant variables and nearly all indices. Almost all indices within each SRI type performed favorably in estimating the plant variables under both salinity levels (6.0 and 12.0 dS m−1) and for the salt-sensitive genotype Sakha 61. The most effective indices extracted from each SRI type by SMLR explained 60%–81% of the total variability in four plant variables. The various predictive models provided a more accurate estimation of Chla and Chlt content than of SDW and Chlb under both salinity levels. They also provided a more accurate estimation of SDW than of Chl content for salt-tolerant genotype Sakha 93, exhibited strong performance for predicting the four variables for Sakha 61, and failed to predict any variables under control and Chlb for Sakha 93. The overall results indicate that the simple form of indices can be used in practice to remotely assess the growth and chlorophyll content of distinct wheat genotypes under saline field conditions. Full article
(This article belongs to the Special Issue Salinity Stress in Plants and Molecular Responses)
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22 pages, 1885 KiB  
Article
Molecular Manipulation of the miR399/PHO2 Expression Module Alters the Salt Stress Response of Arabidopsis thaliana
by Joseph L. Pegler, Jackson M.J. Oultram, Christopher P.L. Grof and Andrew L Eamens
Plants 2021, 10(1), 73; https://doi.org/10.3390/plants10010073 - 31 Dec 2020
Cited by 26 | Viewed by 3888
Abstract
In Arabidopsis thaliana (Arabidopsis), the microRNA399 (miR399)/PHOSPHATE2 (PHO2) expression module is central to the response of Arabidopsis to phosphate (PO4) stress. In addition, miR399 has been demonstrated to also alter in abundance in response to salt [...] Read more.
In Arabidopsis thaliana (Arabidopsis), the microRNA399 (miR399)/PHOSPHATE2 (PHO2) expression module is central to the response of Arabidopsis to phosphate (PO4) stress. In addition, miR399 has been demonstrated to also alter in abundance in response to salt stress. We therefore used a molecular modification approach to alter miR399 abundance to investigate the requirement of altered miR399 abundance in Arabidopsis in response to salt stress. The generated transformant lines, MIM399 and MIR399 plants, with reduced and elevated miR399 abundance respectively, displayed differences in their phenotypic and physiological response to those of wild-type Arabidopsis (Col-0) plants following exposure to a 7-day period of salt stress. However, at the molecular level, elevated miR399 abundance, and therefore, altered PHO2 target gene expression in salt-stressed Col-0, MIM399 and MIR399 plants, resulted in significant changes to the expression level of the two PO4 transporter genes, PHOSPHATE TRANSPORTER1;4 (PHT1;4) and PHT1;9. Elevated PHT1;4 and PHT1;9 PO4 transporter levels in salt stressed Arabidopsis would enhance PO4 translocation from the root to the shoot tissue which would supply additional levels of this precious cellular resource that could be utilized by the aerial tissues of salt stressed Arabidopsis to either maintain essential biological processes or to mount an adaptive response to salt stress. Full article
(This article belongs to the Special Issue Salinity Stress in Plants and Molecular Responses)
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12 pages, 2156 KiB  
Article
Exogenous Salicylic Acid Modulates the Response to Combined Salinity-Temperature Stress in Pepper Plants (Capsicum annuum L. var. Tamarin)
by Ginés Otálora, María Carmen Piñero, Jacinta Collado-González, Josefa López-Marín and Francisco M. del Amor
Plants 2020, 9(12), 1790; https://doi.org/10.3390/plants9121790 - 17 Dec 2020
Cited by 15 | Viewed by 3105
Abstract
Growers in the cultivated areas where the climate change threatens the agricultural productivity and livelihoods are aware that the current constraints for good quality water are being worsened by heatwaves. We studied the combination of salinity (60 mM NaCl) and heat shock stress [...] Read more.
Growers in the cultivated areas where the climate change threatens the agricultural productivity and livelihoods are aware that the current constraints for good quality water are being worsened by heatwaves. We studied the combination of salinity (60 mM NaCl) and heat shock stress (43 °C) in pepper plants (Capsicum annuum L. var. Tamarin) since this can affect physiological and biochemical processes distinctly when compared to separate effects. Moreover, the exogenous application of 0.5 mM salicylic acid (SA) was studied to determine its impacts and the SA-mediated processes that confer tolerance of the combined or stand-alone stresses. Plant growth, leaf Cl− and NO3− concentrations, carbohydrates, and polyamines were analyzed. Our results show that both salinity stress (SS) and heat stress (HS) reduced plant fresh weight, and SA only increased it for HS, with no effect for the combined stress (CS). While SA increased the concentration of Cl− for SS or CS, it had no effect on NO3−. The carbohydrates concentrations were, in general, increased by HS, and were decreased by CS, and for glucose and fructose, by SA. Additionally, when CS was imposed, SA significantly increased the spermine and spermidine concentrations. Thus, SA did not always alleviate the CS and the plant response to CS cannot be directly attributed to the full or partial sum of the individual responses to each stress. Full article
(This article belongs to the Special Issue Salinity Stress in Plants and Molecular Responses)
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19 pages, 3948 KiB  
Article
Germination and Growth of Spinach under Potassium Deficiency and Irrigation with High-Salinity Water
by Kadir Uçgun, Jorge F. S. Ferreira, Xuan Liu, Jaime Barros da Silva Filho, Donald L. Suarez, Claudivan F. de Lacerda and Devinder Sandhu
Plants 2020, 9(12), 1739; https://doi.org/10.3390/plants9121739 - 9 Dec 2020
Cited by 13 | Viewed by 4772
Abstract
Information is scarce on the interaction of mineral deficiency and salinity. We evaluated two salt-tolerant spinach cultivars under potassium (K) doses (0.07, 0.15, 0.3, and 3.0 mmolc L−1) and saline irrigation (5, 30, 60, 120, and 160 mmolc L [...] Read more.
Information is scarce on the interaction of mineral deficiency and salinity. We evaluated two salt-tolerant spinach cultivars under potassium (K) doses (0.07, 0.15, 0.3, and 3.0 mmolc L−1) and saline irrigation (5, 30, 60, 120, and 160 mmolc L−1 NaCl) during germination and growth. There was no interaction between salinity and K. Salinity decreased germination percent (GP), not always significantly, and drastically reduced seedling biomass. ‘Raccoon’ significantly increased GP at 60 mmolc L−1 while ‘Gazelle’ maintained GP up to 60 or 120 mmolc L−1. After 50 days under saline irrigation, shoot biomass increased significantly at 30 and 60 mmolc L−1 at the lowest K dose but, in general, neither salinity nor K dose affected shoot biomass, suggesting that salinity supported plant growth at the most K-deficient dose. Salinity did not affect shoot N, P, or K but significantly reduced Ca, Mg, and S, although plants had no symptoms of salt toxicity or mineral deficiency. Although spinach seedlings are more sensitive to salt stress, plants adjusted to salinity with time. Potassium requirement for spinach growth was less than the current crop recommendation, allowing its cultivation with waters of moderate to high salinity without considerable reduction in yield, appearance, or mineral composition. Full article
(This article belongs to the Special Issue Salinity Stress in Plants and Molecular Responses)
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17 pages, 1335 KiB  
Article
Arbuscular Mycorrhizas Regulate Photosynthetic Capacity and Antioxidant Defense Systems to Mediate Salt Tolerance in Maize
by Hao Wang, Liyan Liang, Baoxing Liu, Di Huang, Shuo Liu, Runjin Liu, Kadambot H.M. Siddique and Yinglong Chen
Plants 2020, 9(11), 1430; https://doi.org/10.3390/plants9111430 - 24 Oct 2020
Cited by 19 | Viewed by 2588
Abstract
Salt stress inhibits photosynthetic process and triggers excessive formation of reactive oxygen species (ROS). This study examined the role of arbuscular mycorrhizal (AM) association in regulating photosynthetic capacity and antioxidant activity in leaves of two maize genotypes (salt-tolerant JD52 and salt-sensitive FSY1) exposed [...] Read more.
Salt stress inhibits photosynthetic process and triggers excessive formation of reactive oxygen species (ROS). This study examined the role of arbuscular mycorrhizal (AM) association in regulating photosynthetic capacity and antioxidant activity in leaves of two maize genotypes (salt-tolerant JD52 and salt-sensitive FSY1) exposed to salt stress (100 mM NaCl) in soils for 21 days. The leaf water content, chlorophyll content, and photosynthetic capacity in non-mycorrhizal (NM) plants were decreased by salt stress, especially in FSY1, with less reduction in AM plants than NM plants. Salinity increased the activities of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR)) in both genotypes regardless of AM inoculation, but decreased the contents of non-enzymatic antioxidants (reduced glutathione (GSH) and ascorbate (AsA)), especially in FSY1, with less decrease in AM plants than NM plants. The AM plants, especially JD52, maintained higher photosynthetic capacity, CO2 fixation efficiency, and ability to preserve membrane integrity than NM plants under salt stress, as also indicated by the higher antioxidant contents and lower malondialdehyde (MDA)/electrolyte leakage in leaves. To conclude, the higher salt tolerance in AM plants correlates with the alleviation of salinity-induced oxidative stress and membrane damage, and the better performance of photosynthesis could have also contributed to this effect through reduced ROS formation. The greater improvements in photosynthetic processes and antioxidant defense systems by AM fungi in FSY1 than JD52 under salinity demonstrate genotypic variation in antioxidant defenses for mycorrhizal amelioration of salt stress. Full article
(This article belongs to the Special Issue Salinity Stress in Plants and Molecular Responses)
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17 pages, 4359 KiB  
Article
The Central Negative Regulator of Flooding Tolerance, the PROTEOLYSIS 6 Branch of the N-degron Pathway, Adversely Modulates Salinity Tolerance in Arabidopsis
by Suman Lamichhane, Jasper B. Alpuerto, Abigail Han and Takeshi Fukao
Plants 2020, 9(11), 1415; https://doi.org/10.3390/plants9111415 - 23 Oct 2020
Cited by 8 | Viewed by 4041
Abstract
Seawater intrusion in coastal regions and waterlogging in salinized lands are serious constraints that reduce crop productivity under changing climate scenarios. Under these conditions, plants encounter flooding and salinity concurrently or sequentially. Identification and characterization of genes and pathways associated with both flooding [...] Read more.
Seawater intrusion in coastal regions and waterlogging in salinized lands are serious constraints that reduce crop productivity under changing climate scenarios. Under these conditions, plants encounter flooding and salinity concurrently or sequentially. Identification and characterization of genes and pathways associated with both flooding and salinity adaptation are critical steps for the simultaneous improvement of plant tolerance to these stresses. The PROTEOLYSIS 6 (PRT6) branch of the N-degron pathway is a well-characterized process that negatively regulates flooding tolerance in plants. Here, we determined the role of the PRT6/N-degron pathway in salinity tolerance in Arabidopsis. This study demonstrates that the prt6 mutation enhances salinity tolerance at the germination, seedling, and adult plant stages. Maintenance of chlorophyll content and root growth under high salt in the prt6 mutant was linked with the restricted accumulation of sodium ions (Na+) in shoots and roots of the mutant genotype. The prt6 mutation also stimulated mRNA accumulation of key transcription factors in ABA-dependent and independent pathways of osmotic/salinity tolerance, accompanied by the prominent expression of their downstream genes. Furthermore, the prt6 mutant displayed increased sensitivity to ethylene and brassinosteroids, which can suppress Na+ uptake and promote the expression of stress-responsive genes. This study provides genetic evidence that both salinity and flooding tolerance is coordinated through a common regulatory pathway in Arabidopsis. Full article
(This article belongs to the Special Issue Salinity Stress in Plants and Molecular Responses)
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8 pages, 4620 KiB  
Communication
In Vitro Plant Evaluation Trial: Reliability Test of Salinity Assays in Citrus Plants
by Margarita Pérez-Jiménez and Olaya Pérez-Tornero
Plants 2020, 9(10), 1352; https://doi.org/10.3390/plants9101352 - 13 Oct 2020
Cited by 13 | Viewed by 3394
Abstract
Salinity is one of the major abiotic stresses affecting crops worldwide, and breeders are urged to evaluate new genotypes to know their degree of tolerance to this selective agent. However, obtaining a number of plants high enough to make the evaluation can prove [...] Read more.
Salinity is one of the major abiotic stresses affecting crops worldwide, and breeders are urged to evaluate new genotypes to know their degree of tolerance to this selective agent. However, obtaining a number of plants high enough to make the evaluation can prove to be a long and laborious process which could be overcome by using tissue culture techniques. In the present study, the reliability of tissue culture evaluations is called into question through two parallel experiments, in vitro and ex vitro, using Citrus macrophylla and four mutants thereof, previously selected by their different behavior to salinity, as a plant material. Plants were subjected to salinity for 8 weeks in both in vitro (80 mM NaCl) and ex vitro (100 mM NaCl) experiments, and differences with plants grown in control conditions without salt were analyzed. After the experiments, length, leaf damage, shoot dry weight, chlorophylls and ions were measured in both conditions and experiments. As a result, it was demonstrated that tissue culture is a reliable tool to determine whether a genotype is tolerant to salinity or not, since plants of the same genotype responded in a similar way to salinity in both experiments. Henceforth, in vitro evaluations can be employed to test genotypes in a very early stage and using very little time and space. However, genotypes that showed the biggest or lowest changes when cultured in salinity were not always the same in both experiments. Thus, only ex vitro experiments can be performed if the goal is to compare genotypes and see which genotype is the most or least resistant to salinity. Full article
(This article belongs to the Special Issue Salinity Stress in Plants and Molecular Responses)
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21 pages, 1175 KiB  
Article
Differences in Physiological and Biochemical Attributes of Wheat in Response to Single and Combined Salicylic Acid and Biochar Subjected to Limited Water Irrigation in Saline Sodic Soil
by Emad M. Hafez, Ahmed M. S. Kheir, Shimaa A. Badawy, Emadeldeen Rashwan, Mohamed Farig and Hany S. Osman
Plants 2020, 9(10), 1346; https://doi.org/10.3390/plants9101346 - 12 Oct 2020
Cited by 35 | Viewed by 3648
Abstract
Given the expectancy of the water supply becoming scarce in the future and more expensive, water conservation during wheat production processes has become very crucial especially in saline sodic soil. Biochar and salicylic acid (SA) were used to assess the potential to alleviate [...] Read more.
Given the expectancy of the water supply becoming scarce in the future and more expensive, water conservation during wheat production processes has become very crucial especially in saline sodic soil. Biochar and salicylic acid (SA) were used to assess the potential to alleviate the influences of depletion of available soil moisture (DAM) on physicochemical, physiological, biochemical attributes, as well as wheat production absorption (Triticum aestivum L. cv. Misr 1) and macro-elements. Two seasons (2018/2019 and 2019/2020) of field trials were investigated using twelve combinations of three water treatments (50%, 70%, and 90% DAM) and foliar- and soil-applied treatments (control, biochar, salicylic acid, and biochar + SA). Biochar treated plots amplified soil physicochemical attributes, leading to improved physiological traits and antioxidant enzymes, as well as yield related traits under water limitation conditions in both years. Similarly, synergistic use of biochar and salicylic acid greatly augmented the designed characteristics such as chlorophyll a, b, K+ content, relative water content (RWC), stomatal conductance, photosynthetic rate, and intrinsic water use efficiency, whilst exhibited inhibitory effects on proline content, electrolyte leakage, Na+ content SOD, POX, CAT, and MDA, consequently increased 1000-grain weight, number of grains spike−1, grain yield, as well nutrient uptake (N, P, K) under water limitation condition in both years, followed by treatment of sole biochar or SA compared to unamended plots treatment (control). Wheat productivity achieved further increasing at 70% DAM alongside synergistic use of biochar and SA which was on par with 50% DAM under unamended plots (control). It is concluded from the findings that coupled application of biochar alongside salicylic acid accomplished an efficient approach to mitigate the injurious influences of water limitation, along with further improvement of the soil, physiology, biochemical attributes, and wheat yield, as well nutrient uptake, under saline sodic soil. Full article
(This article belongs to the Special Issue Salinity Stress in Plants and Molecular Responses)
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15 pages, 2408 KiB  
Article
Zinc and Paclobutrazol Mediated Regulation of Growth, Upregulating Antioxidant Aptitude and Plant Productivity of Pea Plants under Salinity
by Mahmoud R. Sofy, Khalid M. Elhindi, Saad Farouk and Majed A. Alotaibi
Plants 2020, 9(9), 1197; https://doi.org/10.3390/plants9091197 - 14 Sep 2020
Cited by 71 | Viewed by 4866
Abstract
Soil salinity is the main obstacle to worldwide sustainable productivity and food security. Zinc sulfate (Zn) and paclobutrazol (PBZ) as a cost-effective agent, has multiple biochemical functions in plant productivity. Meanwhile, their synergistic effects on inducing salt tolerance are indecisive and not often [...] Read more.
Soil salinity is the main obstacle to worldwide sustainable productivity and food security. Zinc sulfate (Zn) and paclobutrazol (PBZ) as a cost-effective agent, has multiple biochemical functions in plant productivity. Meanwhile, their synergistic effects on inducing salt tolerance are indecisive and not often reported. A pot experiment was done for evaluating the defensive function of Zn (100 mg/L) or PBZ (200 mg/L) on salt (0, 50, 100 mM NaCl) affected pea plant growth, photosynthetic pigment, ions, antioxidant capacity, and yield. Salinity stress significantly reduces all growth and yield attributes of pea plants relative to nonsalinized treatment. This reduction was accompanied by a decline in chlorophyll, nitrogen, phosphorus, and potassium (K+), the ratio between K+ and sodium (Na+), as well as reduced glutathione (GSH) and glutathione reductase (GR). Alternatively, salinity increased Na+, carotenoid (CAR), proline (PRO), ascorbic acid (AsA), superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) over nonsalinized treatment. Foliar spraying with Zn and PBZ under normal condition increased plant growth, nitrogen, phosphorus, potassium, K+/Na+ ratio, CAR, PRO, AsA, GSH, APX, GR, and yield and its quality, meanwhile decreased Na+ over nonsprayed plants. Application of Zn and PBZ counteracted the harmful effects of salinity on pea plants, by upregulating the antioxidant system, ion homeostasis, and improving chlorophyll biosynthesis that induced plant growth and yield components. In conclusion, Zn plus PBZ application at 30 and 45 days from sowing offset the injuries of salinity on pea plant growth and yield by upregulating the antioxidant capacity and increasing photosynthetic pigments. Full article
(This article belongs to the Special Issue Salinity Stress in Plants and Molecular Responses)
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14 pages, 1613 KiB  
Article
Differences in Physiological Responses of Two Oat (Avena nuda L.) Lines to Sodic-Alkalinity in the Vegetative Stage
by Liyun Liu, Nateetorn Petchphankul, Akihiro Ueda and Hirofumi Saneoka
Plants 2020, 9(9), 1188; https://doi.org/10.3390/plants9091188 - 11 Sep 2020
Cited by 7 | Viewed by 2324
Abstract
Sodic-alkalinity is a more seriously limiting factor in agricultural productivity than salinity. Oat (Avena nuda) is a salt-tolerant crop species and is therefore useful in studying the physiological responses of cereals to alkalinity. We evaluated the differential effects of sodic-alkalinity on [...] Read more.
Sodic-alkalinity is a more seriously limiting factor in agricultural productivity than salinity. Oat (Avena nuda) is a salt-tolerant crop species and is therefore useful in studying the physiological responses of cereals to alkalinity. We evaluated the differential effects of sodic-alkalinity on two naked oat lines, Caoyou1 and Yanke1. Seedlings of the two lines were exposed to 50 mM alkaline salt mixture of NaHCO3 and Na2CO3 (18:1 molar ratio; pH 8.5) for 2 weeks in a soil environment. Sodic-alkalinity exposure led the assimilation of abundant Na+ at similar concentrations in the organs of both lines. However, Caoyou1 showed much stronger growth than Yanke1, exhibiting a higher dry weight, total leaf area, and shoot height under sodic-alkalinity. Further analysis showed that Caoyou1 was more sodic-alkalinity tolerance than Yanke1. This was firstly because of differences in the oxidative stress defense mechanisms in leaves of the two lines. Antioxidant enzyme activities were either slightly elevated (catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GP), glutathione reductase (GR)) or unaltered (superoxide dismutase (SOD)) in Caoyou1 leaves, but some enzyme (SOD, GPOX, GR) activities were significantly reduced in Yanke1. AnAPX1 transcript levels significantly increased in Caoyou1 under sodic-alkalinity conditions compared with Yanke1, indicating its better antioxidant capacity. Secondly, the related parameters of Mg2+ concentration, phosphoenolpyruvate carboxylase (PEPC) activity, and AnPEPC transcript levels in the leaves showed significantly higher values in Caoyou1 compared with Yanke1. This demonstrated the effective utilization by Caoyou1 of accumulated HCO3− in the irreversible reaction from phosphoenolpyruvate to oxaloacetate to produce inorganic phosphorus, which was elevated in Caoyou1 leaves under alkalinity stress. Overall, the results demonstrated that the greater sodic-alkalinity tolerance of Caoyou1 is the result of: (1) maintained antioxidant enzyme activities; and (2) a higher capacity for the phosphoenolpyruvate to oxaloacetate reactions, as shown by the higher PEPC activity, Mg2+ concentration, and total phosphorus concentration in its leaves, despite the lower soil pH. Full article
(This article belongs to the Special Issue Salinity Stress in Plants and Molecular Responses)
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17 pages, 1677 KiB  
Article
Arabidopsis Plastid-RNA Polymerase RPOTp Is Involved in Abiotic Stress Tolerance
by Abel Lidón-Soto, Eva Núñez-Delegido, Iván Pastor-Martínez, Pedro Robles and Víctor Quesada
Plants 2020, 9(7), 834; https://doi.org/10.3390/plants9070834 - 2 Jul 2020
Cited by 3 | Viewed by 3364
Abstract
Plastid gene expression (PGE) must adequately respond to changes in both development and environmental cues. The transcriptional machinery of plastids in land plants is far more complex than that of prokaryotes. Two types of DNA-dependent RNA polymerases transcribe the plastid genome: a multimeric [...] Read more.
Plastid gene expression (PGE) must adequately respond to changes in both development and environmental cues. The transcriptional machinery of plastids in land plants is far more complex than that of prokaryotes. Two types of DNA-dependent RNA polymerases transcribe the plastid genome: a multimeric plastid-encoded polymerase (PEP), and a monomeric nuclear-encoded polymerase (NEP). A single NEP in monocots (RPOTp, RNA polymerase of the T3/T7 phage-type) and two NEPs in dicots (plastid-targeted RPOTp, and plastid- and mitochondrial-targeted RPOTmp) have been hitherto identified. To unravel the role of PGE in plant responses to abiotic stress, we investigated if Arabidopsis RPOTp could function in plant salt tolerance. To this end, we studied the sensitivity of T-DNA mutants scabra3-2 (sca3-2) and sca3-3, defective in the RPOTp gene, to salinity, osmotic stress and the phytohormone abscisic acid (ABA) required for plants to adapt to abiotic stress. sca3 mutants were hypersensitive to NaCl, mannitol and ABA during germination and seedling establishment. Later in development, sca3 plants displayed reduced sensitivity to salt stress. A gene ontology (GO) analysis of the nuclear genes differentially expressed in the sca3-2 mutant (301) revealed that many significantly enriched GO terms were related to chloroplast function, and also to the response to several abiotic stresses. By quantitative RT-PCR (qRT-PCR), we found that genes LHCB1 (LIGHT-HARVESTING CHLOROPHYLL a/b-BINDING1) and AOX1A (ALTERNATIVE OXIDASE 1A) were respectively down- and up-regulated in the Columbia-0 (Col-0) salt-stressed plants, which suggests the activation of plastid and mitochondria-to-nucleus retrograde signaling. The transcript levels of genes RPOTp, RPOTmp and RPOTm significantly increased in these salt-stressed seedlings, but this enhanced expression did not lead to the up-regulation of the plastid genes solely transcribed by NEP. Similar to salinity, carotenoid inhibitor norflurazon (NF) also enhanced the RPOTp transcript levels in Col-0 seedlings. This shows that besides salinity, inhibition of chloroplast biogenesis also induces RPOTp expression. Unlike salt and NF, the NEP genes were significantly down-regulated in the Col-0 seedlings grown in ABA-supplemented media. Together, our findings demonstrate that RPOTp functions in abiotic stress tolerance, and RPOTp is likely regulated positively by plastid-to-nucleus retrograde signaling, which is triggered when chloroplast functionality is perturbed by environmental stresses, e.g., salinity or NF. This suggests the existence of a compensatory mechanism, elicited by impaired chloroplast function. To our knowledge, this is the first study to suggest the role of a nuclear-encoded plastid-RNA polymerase in salt stress tolerance in plants. Full article
(This article belongs to the Special Issue Salinity Stress in Plants and Molecular Responses)
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18 pages, 2022 KiB  
Article
Physiological, Biochemical, and Metabolic Responses to Short and Prolonged Saline Stress in Two Cultivated Cardoon Genotypes
by Teresa Docimo, Rosalba De Stefano, Elisa Cappetta, Anna Lisa Piccinelli, Rita Celano, Monica De Palma and Marina Tucci
Plants 2020, 9(5), 554; https://doi.org/10.3390/plants9050554 - 27 Apr 2020
Cited by 21 | Viewed by 3016
Abstract
Cultivated cardoon is a multipurpose crop with adaptability to limiting environments. Two genotypes (“Bianco Avorio” and “Spagnolo”) were comparatively characterized in response to short and prolonged 100 mM NaCl stress in hydroponics. Salt induced no growth variations between genotypes or symptoms of NaCl [...] Read more.
Cultivated cardoon is a multipurpose crop with adaptability to limiting environments. Two genotypes (“Bianco Avorio” and “Spagnolo”) were comparatively characterized in response to short and prolonged 100 mM NaCl stress in hydroponics. Salt induced no growth variations between genotypes or symptoms of NaCl toxicity, but boosted ABA accumulation in roots and leaves. Both genotypes had high constitutive phenol content, whose major components were depleted upon 2 days of stress only in “Bianco Avorio”. Prolonged stress stimulated accumulation of proline, phenylpropanoids, and related transcripts, and non-enzymatic antioxidant activity. Decreased antioxidant enzymes activities upon short stress did not occur for APX in “Spagnolo”, indicating a stronger impairment of enzymatic defenses in “Bianco Avorio”. Nonetheless, H2O2 and lipid peroxidation did not increase under short and prolonged stress in both genotypes. Overall, the two genotypes appear to share similar defense mechanisms but, in the short term, “Bianco Avorio” depends mainly on non-enzymatic antioxidant phenylpropanoids for ROS scavenging, while “Spagnolo” maintains a larger arsenal of defenses. Upon prolonged stress, proline could have contributed to protection of metabolic functions in both genotypes. Our results provide cues that can be exploited for cardoon genetic improvement and highlight genotypic differences for breeding salinity tolerant varieties. Full article
(This article belongs to the Special Issue Salinity Stress in Plants and Molecular Responses)
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