The roles of photorespiration and alternative electron acceptors in the responses of photosynthesis to elevated temperatures in cowpea

Abstract

We explored the effects, on photosynthesis in cowpea (Vigna unguiculata) seedlings, of high temperature and light—environmental stresses that often co‐occur under field conditions and can have greater impact on photosynthesis than either by itself. We observed contrasting responses in the light and carbon assimilatory reactions, whereby in high temperature, the light reactions were stimulated while CO2 assimilation was substantially reduced. There were two striking observations. Firstly, the primary quinone acceptor (QA), a measure of the regulatory balance of the light reactions, became more oxidized with increasing temperature, suggesting increased electron sink capacity, despite the reduced CO2 fixation. Secondly, a strong, O2‐dependent inactivation of assimilation capacity, consistent with down‐regulation of rubisco under these conditions. The dependence of these effects on CO2, O2 and light led us to conclude that both photorespiration and an alternative electron acceptor supported increased electron flow, and thus provided photoprotection under these conditions. Further experiments showed that the increased electron flow was maintained by rapid rates of PSII repair, particularly at combined high light and temperature. Overall, the results suggest that photodamage to the light reactions can be avoided under high light and temperatures by increasing electron sink strength, even when assimilation is strongly suppressed.

Water restriction in cowpea plants [Vigna unguiculata (L.) Walp.]: Metabolic changes and tolerance induction

“…1). Such effects reduce the efficiency of instantaneous carboxylation, due to the unavailability of ATP and NADPH, in addition to the substrate for Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) (Melo et al, 2018b;Osei-Bonsu et al, 2021).…”

The Complementary Roles of Chloroplast Cyclic Electron Transport and Mitochondrial Alternative Oxidase to Ensure Photosynthetic Performance

“…In tomato ( Solanum lycopersicum ), high temperature (40°C) induced the expression of genes encoding components of both CET pathways ( Lu et al, 2020 ). In cowpea ( Vigna unguiculata ), high temperature (45°C) substantially reduced carbon fixation while cETC activity was stimulated and dependent upon photorespiration and other unidentified electron sinks ( Osei-Bonsu et al, 2021 ).…”

Photosystem I Inhibition, Protection and Signalling: Knowns and Unknowns

“…Indeed, a protective effect of elevated CO 2 concentration against PSI photoinhibition during fluctuating light was recently observed, but was reported to be independent from mechanisms induced by thylakoid ΔpH ( Tan et al, 2021 ). On the other hand, PSI oxidation by photorespiration, which is another major chloroplast electron sink that involves oxygenation rather than carboxylation of RuBP, decreases electron pressure at the PSI donor side by oxidising the electron transport chain ( Huang et al, 2015 ; Osei-Bonsu et al, 2021 ) and by inducing lumen acidification and photoprotection ( Furutani et al, 2020 ; Wada et al, 2020 ). Interestingly, weakening of chloroplast sinks in higher plants through down-regulation of CO 2 fixation has been shown to induce photoprotection mechanisms that minimise PSI photoinhibition ( Kohzuma et al, 2009 ; Joliot and Alric, 2013 ; Li Y.T.…”