Pre-illumination at high light significantly alleviates the over-reduction of photosystem I under fluctuating light

Fluctuating light (FL) is a typical natural light stress that can cause photodamage to photosystem I (PSI). However, the effect of growth light on FL-induced PSI photoinhibition remains controversial. Plants grown under high light enhance photorespiration to sustain photosynthesis, but the contribution of photorespiration to PSI photoprotection under FL is largely unknown. In this study, we examined the photosynthetic performance under FL in tomato (Lycopersicon esculentum) plants grown under high light (HL-plants) and moderate light (ML-plants). After an abrupt increase in illumination, the over-reduction of PSI was lowered in HL-plants, resulting in a lower FL-induced PSI photoinhibition. HL-plants displayed higher capacities for CO2 fixation and photorespiration than ML-plants. Within the first 60 s after transition from low to high light, PSII electron transport was much higher in HL-plants, but the gross CO2 assimilation rate showed no significant difference between them. Therefore, upon a sudden increase in illumination, the difference in PSII electron transport between HL- and ML-plants was not attributed to the Calvin–Benson cycle but was caused by the change in photorespiration. These results indicated that the higher photorespiration in HL-plants enhanced the PSI electron sink downstream under FL, which mitigated the over-reduction of PSI and thus alleviated PSI photoinhibition under FL. Taking together, we here for the first time propose that photorespiration acts as a safety valve for PSI photoprotection under FL.

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Drought stress delays photosynthetic induction and accelerates photoinhibition of photosystem I under fluctuating light

10.22541/au.163518994.43126980/v1 ◽

2021 ◽

Author(s):

Hu Sun ◽

Qi Shi ◽

Ning-Yu Liu ◽

Shi-Bao Zhang ◽

Wei Huang

Keyword(s):

Drought Stress ◽

Gas Exchange ◽

Photosystem I ◽

Co2 Fixation ◽

Electron Flow ◽

Photosynthetic Performance ◽

High Light ◽

Carbon Gain ◽

Photosynthetic Induction ◽

Fluctuating Light

Fluctuating light (FL) and drought stress usually occur concomitantly. However, whether drought stress affects photosynthetic performance under FL remains unknown. Here, we measured gas exchange, chlorophyll fluorescence, and P700 redox state under FL in drought-stressed tomato (Solanum lycopersicum) seedlings. Drought stress significantly affected stomatal opening and mesophyll conductance after transition from low to high light and thus delayed photosynthetic induction under FL. Therefore, drought stress exacerbated the loss of carbon gain under FL. Furthermore, restriction of CO2 fixation under drought stress aggravated the over-reduction of photosystem I (PSI) upon transition from low to high light. The resulting stronger FL-induced PSI photoinhibition significantly supressed linear electron flow and PSI photoprotection. These results indicated that drought stress not only affected gas exchange under FL but also accelerated FL-induced photoinhibition of PSI. Furthermore, drought stress enhanced relative cyclic electron flow in FL, which partially compensated for restricted CO2 fixation and thus favored PSI photoprotection under FL. Therefore, drought stress has large effects on photosynthetic dark and light reactions under FL.

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Drought stress delays photosynthetic induction and accelerates photoinhibition of photosystem I under fluctuating light

10.1101/2021.10.07.463522 ◽

2021 ◽

Author(s):

Hu Sun ◽

Qi Shi ◽

Ning-Yu Liu ◽

Shi-Bao Zhang ◽

Wei Huang

Keyword(s):

Drought Stress ◽

Gas Exchange ◽

Photosystem I ◽

Co2 Fixation ◽

Electron Flow ◽

Photosynthetic Performance ◽

High Light ◽

Carbon Gain ◽

Photosynthetic Induction ◽

Fluctuating Light

Fluctuating light (FL) and drought stress usually occur concomitantly. However, whether drought stress affects photosynthetic performance under FL remains unknown. Here, we measured gas exchange, chlorophyll fluorescence, and P700 redox state under FL in drought-stressed tomato (Solanum lycopersicum) seedlings. Drought stress significantly affected stomatal opening and mesophyll conductance after transition from low to high light and thus delayed photosynthetic induction under FL. Therefore, drought stress exacerbated the loss of carbon gain under FL. Furthermore, restriction of CO2 fixation under drought stress aggravated the over-reduction of photosystem I (PSI) upon transition from low to high light. The resulting stronger FL-induced PSI photoinhibition significantly supressed linear electron flow and PSI photoprotection. These results indicated that drought stress not only affected gas exchange under FL but also accelerated FL-induced photoinhibition of PSI. Furthermore, drought stress enhanced relative cyclic electron flow in FL, which partially compensated for restricted CO2 fixation and thus favored PSI photoprotection under FL. Therefore, drought stress has large effects on photosynthetic dark and light reactions under FL.

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

Cells ◽

10.3390/cells11020252 ◽

2022 ◽

Vol 11 (2) ◽

pp. 252

Author(s):

Zhi-Lan Zeng ◽

Hu Sun ◽

Xiao-Qian Wang ◽

Shi-Bao Zhang ◽

Wei Huang

Keyword(s):

Light Intensity ◽

Photosystem I ◽

Light Absorption ◽

High Light Intensity ◽

High Light ◽

Leaf Angle ◽

Sudden Increase ◽

Mature Leaves ◽

Fluctuating Light ◽

Young Leaves

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.

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Physiological and Evolutionary Implications of Tetrameric Photosystem I in Cyanobacteria

10.1101/544353 ◽

2019 ◽

Cited By ~ 2

Author(s):

Meng Li ◽

Alexandra Calteau ◽

Dmitry A. Semchonok ◽

Thomas A. Witt ◽

Jonathan T. Nguyen ◽

...

Keyword(s):

Photosystem I ◽

Genomic Structure ◽

Physiological Role ◽

High Light ◽

Structural Basis ◽

Evolutionary Significance ◽

Phylogenetic Distribution ◽

Physiological Studies ◽

Close Relatives

AbstractPhotosystem I (PSI) were reported as trimeric complexes in most characterized cyanobacteria, yet monomers in plants and algae PSI. Recent reports on tetrameric PSI raised questions regarding its structural basis, physiological role, phylogenetic distribution and evolutionary significance. In this study, by examining PSI in 61 cyanobacteria, we show that tetrameric PSI, correlating with a unique psaL gene and genomic structure, is widespread in the heterocyst-forming cyanobacteria and their close relatives. Physiological studies on these cyanobacteria revealed that tetrameric PSI is favored under high light, with an increased content of novel PSI-bound carotenoids (myxoxanthophyll, canthaxanthan and echinenone). Together this work suggests that tetrameric PSI is an adaptation to high light, along with results showing that change in PsaL leads to trimeric PSI monomerization, supporting the hypothesis of tetrameric PSI being the evolutionary intermediate in the transition from cyanobacterial trimeric PSI to monomeric PSI in plants and algae.

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The water-water cycle is more effective in regulating redox state of photosystem I under fluctuating light than cyclic electron transport

Biochimica et Biophysica Acta (BBA) - Bioenergetics ◽

10.1016/j.bbabio.2020.148235 ◽

2020 ◽

Vol 1861 (9) ◽

pp. 148235 ◽

Cited By ~ 3

Author(s):

Hu Sun ◽

Ying-Jie Yang ◽

Wei Huang

Keyword(s):

Electron Transport ◽

Photosystem I ◽

Redox State ◽

Water Cycle ◽

Cyclic Electron Transport ◽

Fluctuating Light

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The Response Regulator RpaB Binds to the Upstream Element of Photosystem I Genes To Work for Positive Regulation under Low-Light Conditions in Synechocystis sp. Strain PCC 6803

Journal of Bacteriology ◽

10.1128/jb.01588-08 ◽

2008 ◽

Vol 191 (5) ◽

pp. 1581-1586 ◽

Cited By ~ 29

Author(s):

Yurie Seino ◽

Tomoko Takahashi ◽

Yukako Hihara

Keyword(s):

Photosystem I ◽

Promoter Activity ◽

Response Regulator ◽

Core Promoter ◽

High Light ◽

Light Conditions ◽

Low Light ◽

Positive Regulation ◽

Upstream Element ◽

Pcc 6803

ABSTRACT The coordinated high-light response of genes encoding subunits of photosystem I (PSI) is achieved by the AT-rich region located just upstream of the core promoter in Synechocystis sp. strain PCC 6803. The upstream element enhances the basal promoter activity under low-light conditions, whereas this positive regulation is lost immediately after the shift to high-light conditions. In this study, we focused on a high-light regulatory 1 (HLR1) sequence included in the upstream element of every PSI gene examined. A gel mobility shift assay revealed that a response regulator RpaB binds to the HLR1 sequence in PSI promoters. Base substitution in the HLR1 sequence or decrease in copy number of the rpaB gene resulted in decrease in the promoter activity of PSI genes under low-light conditions. These observations suggest that RpaB acts as a transcriptional activator for PSI genes. It is likely that RpaB binds to the HLR1 sequence under low-light conditions and works for positive regulation of PSI genes and for negative regulation of high-light-inducible genes depending on the location of the HLR1 sequence within target promoters.

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