Cells

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19 pages, 8419 KiB

Open AccessArticle

Potential Role of Low-Molecular-Weight Dioxolanes as Adjuvants for Glyphosate-Based Herbicides Using Photosystem II as an Early Post-Treatment Determinant

by Ewa Szwajczak, Edyta Sierka and Michał Ludynia

Cells 2023, 12(5), 777; https://doi.org/10.3390/cells12050777 - 28 Feb 2023

Cited by 1 | Viewed by 1624

Abstract

Pesticide use cannot be completely abandoned in modern agriculture. Among agrochemicals, glyphosate is one of the most popular and, at the same time, most divisive herbicide. Since the chemicalization of agriculture is detrimental, various attempts are being made to reduce it. Adjuvants—substances that [...] Read more.

Pesticide use cannot be completely abandoned in modern agriculture. Among agrochemicals, glyphosate is one of the most popular and, at the same time, most divisive herbicide. Since the chemicalization of agriculture is detrimental, various attempts are being made to reduce it. Adjuvants—substances that increase the efficiency of foliar application—can be used to reduce the amount of herbicides used. We propose low-molecular-weight dioxolanes as adjuvants for herbicides. These compounds quickly convert to carbon dioxide and water and do not harm plants. The aim of this study was to evaluate the efficacy of RoundUp^® 360 Plus supported by three potential adjuvants: 2,2-dimethyl-1,3-dioxolane (DMD), 2,2,4-trimethyl-1,3-dioxolane (TMD), and (2,2-dimethyl-1,3-dioxan-4-yl)methanol (DDM), on a common weed species Chenopodium album L., under greenhouse conditions. Chlorophyll a fluorescence parameters and analysis of the polyphasic fluorescence (OJIP) curve, which examines changes in the photochemical efficiency of photosystem II, were used to measure plant sensitivity to glyphosate stress and verified the efficacy achieved by tested formulations. The effective dose (ED) values obtained showed that the weed tested was sensitive to reduced doses of glyphosate, with 720 mg/L needed to achieve 100% effectiveness. Compared to the glyphosate assisted with DMD, TMD, and DDM, ED was reduced by 40%, 50%, and 40%, respectively. The application of all dioxolanes at a concentration equal to 1 vol.% significantly enhanced the herbicide’s effect. Our study showed that for C. album there was a correlation between the change in OJIP curve kinetics and the applied dose of glyphosate. By analyzing the discrepancies in the curves, it is possible to show the effect of different herbicide formulations with or without dioxolanes at an early stage of its action, thus minimizing the time for testing new substances as adjuvants. Full article

(This article belongs to the Special Issue Understanding the Photosynthesis Process Using Chlorophyll Fluorescence)

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13 pages, 1296 KiB

Open AccessArticle

Regulation of Chloroplast ATP Synthase Modulates Photoprotection in the CAM Plant Vanilla planifolia

by Hui Wang, Xiao-Qian Wang, Yi-Zhang Xing, Qing-Yun Zhao, Hui-Fa Zhuang and Wei Huang

Cells 2022, 11(10), 1647; https://doi.org/10.3390/cells11101647 - 15 May 2022

Cited by 3 | Viewed by 3006

Abstract

Generally, regulation of cyclic electron flow (CEF) and chloroplast ATP synthase play key roles in photoprotection for photosystems I and II (PSI and PSII) in C3 and C4 plants, especially when CO₂ assimilation is restricted. However, how CAM plants protect PSI and [...] Read more.

Generally, regulation of cyclic electron flow (CEF) and chloroplast ATP synthase play key roles in photoprotection for photosystems I and II (PSI and PSII) in C3 and C4 plants, especially when CO₂ assimilation is restricted. However, how CAM plants protect PSI and PSII when CO₂ assimilation is restricted is largely known. In the present study, we measured PSI, PSII, and electrochromic shift signals in the CAM plant Vanilla planifolia. The quantum yields of PSI and PSII photochemistry largely decreased in the afternoon compared to in the morning, indicating that CO₂ assimilation was strongly restricted in the afternoon. Meanwhile, non-photochemical quenching (NPQ) in PSII and the donor side limitation of PSI (Y(ND)) significantly increased to protect PSI and PSII. Under such conditions, proton gradient (∆pH) across the thylakoid membranes largely increased and CEF was slightly stimulated, indicating that the increased ∆pH was not caused by the regulation of CEF. In contrast, the activity of chloroplast ATP synthase (g_H⁺) largely decreased in the afternoon. At a given proton flux, the decreasing g_H⁺ increased ∆pH and thus contributed to the enhancement of NPQ and Y(ND). Therefore, in the CAM plant V. planifolia, the ∆pH-dependent photoprotective mechanism is mainly regulated by the regulation of g_H⁺ rather than CEF when CO₂ assimilation is restricted. Full article

(This article belongs to the Special Issue Understanding the Photosynthesis Process Using Chlorophyll Fluorescence)

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16 pages, 2385 KiB

Open AccessArticle

Molecular and Photosynthetic Performance in the Yellow Leaf Mutant of Torreya grandis According to Transcriptome Sequencing, Chlorophyll a Fluorescence, and Modulated 820 nm Reflection

by Jianshuang Shen, Xueqin Li, Xiangtao Zhu, Zhicheng Ding, Xiaoling Huang, Xia Chen and Songheng Jin

Cells 2022, 11(3), 431; https://doi.org/10.3390/cells11030431 - 27 Jan 2022

Cited by 8 | Viewed by 2672

Abstract

To study the photosynthetic energy mechanism and electron transfer in yellow leaves, transcriptomics combined with physiological approaches was used to explore the mechanism of the yellow leaf mutant Torreya grandis ‘Merrillii’. The results showed that chlorophyll content, the maximal photochemical efficiency of PSII [...] Read more.

To study the photosynthetic energy mechanism and electron transfer in yellow leaves, transcriptomics combined with physiological approaches was used to explore the mechanism of the yellow leaf mutant Torreya grandis ‘Merrillii’. The results showed that chlorophyll content, the maximal photochemical efficiency of PSII (F_v/F_m), and the parameters related to the OJ phase of fluorescence (φ_Eo, φ_Ro) were all decreased significantly in mutant-type T. grandis leaves. The efficiency needed for an electron to be transferred from the reduced carriers between the two photosystems to the end acceptors of the PSI (δ_Ro) and the quantum yield of the energy dissipation (φ_Do) were higher in the leaves of mutant-type T. grandis compared to those in wild-type leaves. Analysis of the prompt fluorescence kinetics and modulated 820 nm reflection showed that the electron transfer of PSII was decreased, and PSI activity was increased in yellow T. grandis leaves. Transcriptome data showed that the unigenes involved in chlorophyll synthesis and the photosynthetic electron transport complex were downregulated in the leaves of mutant-type T. grandis compared to wild-type leaves, while there were no observable changes in carotenoid content and biosynthesis. These findings suggest that the downregulation of genes involved in chlorophyll synthesis leads to decreased chlorophyll content, resulting in both PSI activity and carotenoids having higher tolerance when acting as photo-protective mechanisms for coping with chlorophyll deficit and decrease in linear electron transport in PSII. Full article

(This article belongs to the Special Issue Understanding the Photosynthesis Process Using Chlorophyll Fluorescence)

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13 pages, 2337 KiB

Open AccessArticle

Regulation of Leaf Angle Protects Photosystem I under Fluctuating Light in Tobacco Young Leaves

by Zhi-Lan Zeng, Hu Sun, Xiao-Qian Wang, Shi-Bao Zhang and Wei Huang

Cells 2022, 11(2), 252; https://doi.org/10.3390/cells11020252 - 12 Jan 2022

Cited by 4 | Viewed by 1974

Abstract

Fluctuating light is a typical light condition in nature and can cause selective photodamage to photosystem I (PSI). The sensitivity of PSI to fluctuating light is influenced by the amplitude of low/high light intensity. Tobacco mature leaves are tended to be horizontal to [...] Read more.

Fluctuating light is a typical light condition in nature and can cause selective photodamage to photosystem I (PSI). The sensitivity of PSI to fluctuating light is influenced by the amplitude of low/high light intensity. Tobacco mature leaves are tended to be horizontal to maximize the light absorption and photosynthesis, but young leaves are usually vertical to diminish the light absorption. Therefore, we tested the hypothesis that such regulation of the leaf angle in young leaves might protect PSI against photoinhibition under fluctuating light. We found that, upon a sudden increase in illumination, PSI was over-reduced in extreme young leaves but was oxidized in mature leaves. After fluctuating light treatment, such PSI over-reduction aggravated PSI photoinhibition in young leaves. Furthermore, the leaf angle was tightly correlated to the extent of PSI photoinhibition induced by fluctuating light. Therefore, vertical young leaves are more susceptible to PSI photoinhibition than horizontal mature leaves when exposed to the same fluctuating light. In young leaves, the vertical leaf angle decreased the light absorption and thus lowered the amplitude of low/high light intensity. Therefore, the regulation of the leaf angle was found for the first time as an important strategy used by young leaves to protect PSI against photoinhibition under fluctuating light. To our knowledge, we show here new insight into the photoprotection for PSI under fluctuating light in nature. Full article

(This article belongs to the Special Issue Understanding the Photosynthesis Process Using Chlorophyll Fluorescence)

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16 pages, 3331 KiB

Open AccessArticle

Effect of Drought and Heavy Metal Contamination on Growth and Photosynthesis of Silver Birch Trees Growing on Post-Industrial Heaps

by Krzysztof Sitko, Magdalena Opała-Owczarek, Gabriela Jemioła, Żaneta Gieroń, Michał Szopiński, Piotr Owczarek, Małgorzata Rudnicka and Eugeniusz Małkowski

Cells 2022, 11(1), 53; https://doi.org/10.3390/cells11010053 - 24 Dec 2021

Cited by 19 | Viewed by 4344

Abstract

Silver birch trees (Betula pendula Roth) are a pioneering species in post-industrial habitats, and have been associated with an expansive breeding strategy and low habitat requirements. We conducted ecophysiological and dendroclimatological studies to check whether there are any features of which the [...] Read more.

Silver birch trees (Betula pendula Roth) are a pioneering species in post-industrial habitats, and have been associated with an expansive breeding strategy and low habitat requirements. We conducted ecophysiological and dendroclimatological studies to check whether there are any features of which the modification enables birch trees to colonise extreme habitats successfully. We characterised the efficiency of the photosynthetic apparatus, the gas exchange, the content of pigments in leaves, and the growth (leaf thickness and tree-ring width) of birch trees on a post-coal mine heap, a post-smelter heap, and a reference site. Birch growth was limited mainly by temperature and water availability during summer, and the leaves of the birch growing on post-industrial heaps were significantly thicker than the reference leaves. Moreover, birch trees growing on heaps were characterised by a significantly higher content of flavonols and anthocyanins in leaves and higher non-photochemical quenching. In addition, birches growing on the post-coal mine heap accumulated a concentration of Mn in their leaves, which is highly toxic for most plant species. Increasing the thickness of leaves, and the content of flavonols and anthocyanins, as well as efficient non-photochemical quenching seem to be important features that improve the colonization of extreme habitats by birches. Full article

(This article belongs to the Special Issue Understanding the Photosynthesis Process Using Chlorophyll Fluorescence)

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13 pages, 2225 KiB

Open AccessArticle

Diurnal Response of Photosystem I to Fluctuating Light Is Affected by Stomatal Conductance

by Ting-Yu Li, Qi Shi, Hu Sun, Ming Yue, Shi-Bao Zhang and Wei Huang

Cells 2021, 10(11), 3128; https://doi.org/10.3390/cells10113128 - 11 Nov 2021

Cited by 14 | Viewed by 2276

Abstract

Upon a sudden transition from low to high light, electrons transported from photosystem II (PSII) to PSI should be rapidly consumed by downstream sinks to avoid the over-reduction of PSI. However, the over-reduction of PSI under fluctuating light might be accelerated if primary [...] Read more.

Upon a sudden transition from low to high light, electrons transported from photosystem II (PSII) to PSI should be rapidly consumed by downstream sinks to avoid the over-reduction of PSI. However, the over-reduction of PSI under fluctuating light might be accelerated if primary metabolism is restricted by low stomatal conductance. To test this hypothesis, we measured the effect of diurnal changes in stomatal conductance on photosynthetic regulation under fluctuating light in tomato (Solanum lycopersicum) and common mulberry (Morus alba). Under conditions of high stomatal conductance, we observed PSI over-reduction within the first 10 s after transition from low to high light. Lower stomatal conductance limited the activity of the Calvin–Benson–Bassham cycle and aggravated PSI over-reduction within 10 s after the light transition. We also observed PSI over-reduction after transition from low to high light for 30 s at the low stomatal conductance typical of the late afternoon, indicating that low stomatal conductance extends the period of PSI over-reduction under fluctuating light. Therefore, diurnal changes in stomatal conductance significantly affect the PSI redox state under fluctuating light. Moreover, our analysis revealed an unexpected inhibition of cyclic electron flow by the severe over-reduction of PSI seen at low stomatal conductance. In conclusion, stomatal conductance can have a large effect on thylakoid reactions under fluctuating light. Full article

(This article belongs to the Special Issue Understanding the Photosynthesis Process Using Chlorophyll Fluorescence)

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15 pages, 17312 KiB

Open AccessFeature PaperArticle

Elevated CO₂ Concentration Alters Photosynthetic Performances under Fluctuating Light in Arabidopsis thaliana

by Shun-Ling Tan, Xing Huang, Wei-Qi Li, Shi-Bao Zhang and Wei Huang

Cells 2021, 10(9), 2329; https://doi.org/10.3390/cells10092329 - 6 Sep 2021

Cited by 9 | Viewed by 2574

Abstract

In view of the current and expected future rise in atmospheric CO₂ concentrations, we examined the effect of elevated CO₂ on photoinhibition of photosystem I (PSI) under fluctuating light in Arabidopsis thaliana. At 400 ppm CO₂, PSI showed [...] Read more.

In view of the current and expected future rise in atmospheric CO₂ concentrations, we examined the effect of elevated CO₂ on photoinhibition of photosystem I (PSI) under fluctuating light in Arabidopsis thaliana. At 400 ppm CO₂, PSI showed a transient over-reduction within the first 30 s after transition from dark to actinic light. Under the same CO₂ conditions, PSI was highly reduced after a transition from low to high light for 20 s. However, such PSI over-reduction greatly decreased when measured in 800 ppm CO₂, indicating that elevated atmospheric CO₂ facilitates the rapid oxidation of PSI under fluctuating light. Furthermore, after fluctuating light treatment, residual PSI activity was significantly higher in 800 ppm CO₂ than in 400 ppm CO₂, suggesting that elevated atmospheric CO₂ mitigates PSI photoinhibition under fluctuating light. We further demonstrate that elevated CO₂ does not affect PSI activity under fluctuating light via changes in non-photochemical quenching or cyclic electron transport, but rather from a rapid electron sink driven by CO₂ fixation. Therefore, elevated CO₂ mitigates PSI photoinhibition under fluctuating light at the acceptor rather than the donor side. Taken together, these observations indicate that elevated atmospheric CO₂ can have large effects on thylakoid reactions under fluctuating light. Full article

(This article belongs to the Special Issue Understanding the Photosynthesis Process Using Chlorophyll Fluorescence)

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23 pages, 5303 KiB

Open AccessArticle

Blue Light Improves Photosynthetic Performance and Biomass Partitioning toward Harvestable Organs in Saffron (Crocus sativus L.)

by Shirin Moradi, Mohsen Kafi, Sasan Aliniaeifard, Seyed Alireza Salami, Majid Shokrpour, Carsten Pedersen, Moein Moosavi-Nezhad, Jacek Wróbel and Hazem M. Kalaji

Cells 2021, 10(8), 1994; https://doi.org/10.3390/cells10081994 - 5 Aug 2021

Cited by 36 | Viewed by 5566

Abstract

Saffron is a valuable plant and one of the most expensive spices worldwide. Nowadays, there is a tendency to produce this crop in indoor plant production systems. However, the production of saffron is restricted by the need for the reproduction of high-quality corms. [...] Read more.

Saffron is a valuable plant and one of the most expensive spices worldwide. Nowadays, there is a tendency to produce this crop in indoor plant production systems. However, the production of saffron is restricted by the need for the reproduction of high-quality corms. In this study, we investigated the effect of different ratios of red (R) and blue (B) light spectra (including 100% B (monochromatic B), 75%, 50%, 40%, 25% B, and 0% B (monochromatic R) on the photosynthetic performance and biomass partitioning as well as morphological and biochemical characteristics of saffron. The growth of flower, root, and corm was improved by increasing the proportion of B to R light. B-grown plants were characterized by the highest photosynthetic functionality with efficient electron transport and lower energy dissipation when compared to R-grown plants. B light directed biomass toward the corms and floral organs, while R light directed it toward the leaves. In saffron, the weight of a daughter corm is of great importance since it determines the yield of the next year. As the ratio of B to R light increased, the daughter corms also became heavier, at the cost of reducing their number, though increasing the proportion of B-enhanced antioxidant capacity as well as the activity of ascorbate peroxidase and catalase while superoxide dismutase activity was enhanced in R-grown plants. In conclusion, B light increased the production of high-quality daughter corms and altered biomass partitioning towards harvestable organs (corms and flowers) in saffron plants. Full article

(This article belongs to the Special Issue Understanding the Photosynthesis Process Using Chlorophyll Fluorescence)

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24 pages, 8363 KiB

Open AccessArticle

Synergistic Effects of Melatonin and Gamma-Aminobutyric Acid on Protection of Photosynthesis System in Response to Multiple Abiotic Stressors

by Aida Shomali, Sasan Aliniaeifard, Fardad Didaran, Mahmoud Lotfi, Mohammad Mohammadian, Mehdi Seif, Wacław Roman Strobel, Edyta Sierka and Hazem M. Kalaji

Cells 2021, 10(7), 1631; https://doi.org/10.3390/cells10071631 - 29 Jun 2021

Cited by 43 | Viewed by 4511

Abstract

GABA (gamma-aminobutyric acid) and melatonin are endogenous compounds that enhance plant responses to abiotic stresses. The response of Vicia faba to different stressors (salinity (NaCl), poly ethylene glycol (PEG), and sulfur dioxide (SO₂)) was studied after priming with sole application of [...] Read more.

GABA (gamma-aminobutyric acid) and melatonin are endogenous compounds that enhance plant responses to abiotic stresses. The response of Vicia faba to different stressors (salinity (NaCl), poly ethylene glycol (PEG), and sulfur dioxide (SO₂)) was studied after priming with sole application of GABA and melatonin or their co-application (GABA + melatonin). Both melatonin and GABA and their co-application increased leaf area, number of flowers, shoot dry and fresh weight, and total biomass. Plants treated with GABA, melatonin, and GABA + melatonin developed larger stomata with wider aperture compared to the stomata of control plants. The functionality of the photosynthetic system was improved in primed plants. To investigate the photosynthetic functionality in details, the leaf samples of primed plants were exposed to different stressors, including SO₂, PEG, and NaCl. The maximum quantum yield of photosystem II (PS II) was higher in the leaf samples of primed plants, while the non-photochemical quenching (NPQ) of primed plants was decreased when leaf samples were exposed to the stressors. Correlation analysis showed the association of initial PI_abs with post-stress F_V/F_M and NPQ. Stressors attenuated the association of initial PI_abs with both F_V/F_M and NPQ, while priming plants with GABA, melatonin, or GABA + melatonin minimized the effect of stressors by attenuating these correlations. In conclusion, priming plants with both GABA and melatonin improved growth and photosynthetic performance of Vicia faba and mitigated the effects of abiotic stressors on the photosynthetic performance. Full article

(This article belongs to the Special Issue Understanding the Photosynthesis Process Using Chlorophyll Fluorescence)

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13 pages, 2575 KiB

Open AccessArticle

Different Strategies for Photosynthetic Regulation under Fluctuating Light in Two Sympatric Paphiopedilum Species

by Jing-Qiu Feng, Wei Huang, Ji-Hua Wang and Shi-Bao Zhang

Cells 2021, 10(6), 1451; https://doi.org/10.3390/cells10061451 - 10 Jun 2021

Cited by 5 | Viewed by 2598

Abstract

Fluctuating light can cause selective photoinhibition of photosystem I (PSI) in angiosperms. Cyclic electron flow (CEF) around PSI and electron flux from water via the electron transport chain to oxygen (the water-water cycle) play important roles in coping with fluctuating light in angiosperms. [...] Read more.

Fluctuating light can cause selective photoinhibition of photosystem I (PSI) in angiosperms. Cyclic electron flow (CEF) around PSI and electron flux from water via the electron transport chain to oxygen (the water-water cycle) play important roles in coping with fluctuating light in angiosperms. However, it is unclear whether plant species in the same genus employ the same strategy to cope with fluctuating light. To answer this question, we measured P700 redox kinetics and chlorophyll fluorescence under fluctuating light in two Paphiopedilum (P.) Pftzer (Orchidaceae) species, P. dianthum and P. micranthum. After transition from dark to high light, P. dianthum displayed a rapid re-oxidation of P700, while P. micranthum displayed an over-reduction of P700. Furthermore, the rapid re-oxidation of P700 in P. dianthum was not observed when measured under anaerobic conditions. These results indicated that photo-reduction of O₂ mediated by the water-water cycle was functional in P. dianthum but not in P. micranthum. Within the first few seconds after an abrupt transition from low to high light, PSI was highly oxidized in P. dianthum but was highly reduced in P. micranthum, indicating that the different responses of PSI to fluctuating light between P. micranthum and P. dianthum was attributed to the water-water cycle. In P. micranthum, the lack of the water-water cycle was partially compensated for by an enhancement of CEF. Taken together, P. dianthum and P. micranthum employed different strategies to cope with the abrupt change of light intensity, indicating the diversity of strategies for photosynthetic acclimation to fluctuating light in these two closely related orchid species. Full article

(This article belongs to the Special Issue Understanding the Photosynthesis Process Using Chlorophyll Fluorescence)

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15 pages, 3389 KiB

Open AccessArticle

Functional Characterization of the Photosynthetic Machinery in Smicronix Galls on the Parasitic Plant Cuscuta campestris by JIP-Test

by Lyuben Zagorchev, Alexandra Atanasova, Ivanela Albanova, Anelia Traianova, Petko Mladenov, Margarita Kouzmanova, Vasilij Goltsev, Hazem M. Kalaji and Denitsa Teofanova

Cells 2021, 10(6), 1399; https://doi.org/10.3390/cells10061399 - 5 Jun 2021

Cited by 17 | Viewed by 4146

Abstract

Members of the genus Cuscuta are generally considered to be non-photosynthetic, stem-holoparasitic flowering plants. Under certain circumstances, at least some members of the genus are capable of limited photosynthesis. The galls of the Smicronyx weevils formed on Cuscuta campestris are particularly rich in [...] Read more.

Members of the genus Cuscuta are generally considered to be non-photosynthetic, stem-holoparasitic flowering plants. Under certain circumstances, at least some members of the genus are capable of limited photosynthesis. The galls of the Smicronyx weevils formed on Cuscuta campestris are particularly rich in chlorophylls compared to the stem of the parasitic plant. In the present study, we aimed to characterize the photosynthetic activity in the inner and outer gall cortices in comparison to the non-photosynthetic stems and a reference plant (Arabidopsis thaliana). The recorded prompt chlorophyll fluorescence transients were analyzed using JIP test. Detailed analysis of the chlorophyll fluorescence confirmed the presence of actively functioning photosynthetic machinery, especially in the inner cortex of the galls. This photosynthesis, induced by the insect larvae, did not reach the levels of the photosynthetic activity in Arabidopsis thaliana plants. Thylakoid protein complexes were identified by separation with two-dimensional Blue Native/SDS PAGE. It appeared that some of the complexes presented in A. thaliana are missing in C. campestris. We hypothesize that the insect-triggered transition from non-photosynthetic to photosynthetic tissue in the gall is driven by the increased requirements for nutrients related to the larval nutrition. Full article

(This article belongs to the Special Issue Understanding the Photosynthesis Process Using Chlorophyll Fluorescence)

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18 pages, 7334 KiB

Open AccessArticle

Tenuazonic Acid-Triggered Cell Death Is the Essential Prerequisite for Alternaria alternata (Fr.) Keissler to Infect Successfully Host Ageratina adenophora

by Jiale Shi, Min Zhang, Liwen Gao, Qian Yang, Hazem M. Kalaji, Sheng Qiang, Reto Jörg Strasser and Shiguo Chen

Cells 2021, 10(5), 1010; https://doi.org/10.3390/cells10051010 - 25 Apr 2021

Cited by 20 | Viewed by 3072

Abstract

The necrotrophic fungus Alternaria alternata contains different pathotypes that produce different mycotoxins. The pathotype Ageratina adenophora secretes the non-host-selective toxin tenuazonic acid (TeA), which can cause necrosis in many plants. Although TeA is thought to be a central virulence factor of the A. [...] Read more.

The necrotrophic fungus Alternaria alternata contains different pathotypes that produce different mycotoxins. The pathotype Ageratina adenophora secretes the non-host-selective toxin tenuazonic acid (TeA), which can cause necrosis in many plants. Although TeA is thought to be a central virulence factor of the A. adenophora pathotype, the precise role of TeA in different stages of host infection by pathogens remains unclear. Here, an A. alternata wild-type and the toxin-deficient mutant ΔHP001 with a 75% reduction in TeA production were used. It was observed that wild-type pathogens could induce the reactive oxygen species (ROS) bursts in host leaves and killed photosynthetic cells before invading hyphae. The ROS interceptor catalase remarkably inhibited hyphal penetration and invasive hyphal growth and expansion in infected leaves and suppressed necrotic leaf lesion. This suggests that the production of ROS is critical for pathogen invasion and proliferation and disease symptom formation during infection. It was found that the mutant pathogens did not cause the formation of ROS and cell death in host leaves, showing an almost complete loss of disease susceptibility. In addition, the lack of TeA resulted in a significant reduction in the ability of the pathogen to penetrate invasive hyphal growth and spread. The addition of exogenous TeA, AAL-toxin, and bentazone to the mutant ΔHP001 pathogens during inoculation resulted in a significant restoration of pathogenicity by increasing the level of cell death, frequency of hyphal penetration, and extent of invasive hyphal spread. Our results suggest that cell death triggered by TeA is the essential requirement for successful colonization and disease development in host leaves during infection with A. adenophora pathogens. Full article

(This article belongs to the Special Issue Understanding the Photosynthesis Process Using Chlorophyll Fluorescence)

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