Journal
PLANTS-BASEL
Volume 8, Issue 6, Pages -Publisher
MDPI
DOI: 10.3390/plants8060152
Keywords
charge recombination; cyclic electron flow; ferredoxin; photosystem I; P700; reactive oxygen species
Categories
Funding
- [AL65D21010]
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Oxygen (O-2)-evolving photosynthetic organisms oxidize the reaction center chlorophyll, P700, in photosystem I (PSI) to suppress the production of reactive oxygen species. The oxidation of P700 is accompanied by alternative electron flow in PSI (AEF-I), which is not required for photosynthetic linear electron flow (LEF). To characterize AEF-I, we compared the redox reactions of P700 and ferredoxin (Fd) during the induction of carbon dioxide (CO2) assimilation in wheat leaves, using dark-interval relaxation kinetics analysis. Switching on an actinic light (1000 mu mol photons m(-2) s(-1)) at ambient CO2 partial pressure of 40 Pa and ambient O-2 partial pressure of 21 kPa gradually oxidized P700 (P700(+)) and enhanced the reduction rate of P700(+) (vP700) and oxidation rate of reduced Fd (vFd). The vFd showed a positive linear relationship with an apparent photosynthetic quantum yield of PSII (Y[II]) originating at point zero; the redox turnover of Fd is regulated by LEF via CO2 assimilation and photorespiration. The vP700 also showed a positive linear relationship with Y(II), but the intercept was positive, not zero. That is, the electron flux in PSI included the electron flux in AEF-I in addition to that in LEF. This indicates that the oxidation of P700 induces AEF-I. We propose a possible mechanism underlying AEF-I and its physiological role in the mitigation of oxidative damage.
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