Reduction of the primary donor P700 of photosystem I during steady-state photosynthesis under low light in Arabidopsis

Abstract

During steady-state photosynthesis in low-light, 830-nm absorption (A(830)) by leaves was close to that in darkness in Arabidopsis, indicating that the primary donor P700 in the reaction center of photosystem I (PSI) was in reduced form. However, P700 was not fully oxidized by a saturating light pulse, suggesting the presence of a population of PSI centers with reduced P700 that remains thermodynamically stable during the application of the saturating light pulse (i.e., reduced-inactive P700). To substantiate this, the effects of methyl viologen (MV) and far-red light on P700 oxidation by the saturating light pulse were analyzed, and the cumulative effects of repetitive application of the saturating light pulse on photosynthesis were analyzed using a mutant crr2-2 with impaired PSI cyclic electron flow. We concluded that the reduced-inactive P700 in low-light as revealed by saturating light pulse indicates limitations of electron flow at the PSI acceptor side.

PROTON GRADIENT REGULATION5 Is Essential for Proper Acclimation of Arabidopsis Photosystem I to Naturally and Artificially Fluctuating Light Conditions

“…By contrast, the pgr5 mutant is not able to protonate the lumen and therefore fails in downregulation of the Cyt b 6 f complex, which in turn results in overreduction of the entire intersystem ETC. For this reason, upon the high light pulse, an excess of electrons strikes out to PSI and causes overreduction ( Figure 5C) and eventually an irreversible damage of the PSI acceptor side (Tsuyama and Kobayashi, 2009). Incapability of pgr5 to induce NPQ ( Figure 5D) possibly somewhat reinforces the PSI injury due to the fact that the pgr5 mutant cannot downregulate PSII via heat dissipation of the excess excitation energy.…”

Degradation of the Herbicides Clomazone, Paraquat, and Glyphosate by Thermally Activated Peroxydisulfate

“…In particular, glyphosate (GS), clomazone (CLO), and paraquat (PQ) are among the most widely used broad-spectrum herbicides. They have very different mechanisms of action because of their differences in chemical structures: GS controls weeds by inhibiting the synthesis of aromatic amino acids necessary for protein formation in susceptible plants (6); CLO inhibits synthesis of chlorophyll and carotenoids in sensitive plants, resulting in foliage devoid of pigmentation (7); and PQ inhibits photosynthesis by accepting electrons from photosystem I in light-exposed plants (8).…”