Relation between the mode of binding of nitrite and the energy distribution between the two photosystems

Abstract

The reversibility of nitrite‐induced inhibition in relation to energy distribution between the two photosystems was studied in spinach thylakoid membranes. Measurements of electron transfer rate catalyzed by photosystem I (PS I) and photosystem II (PS II), chlorophyll a (Chl a) fluorescence induction kinetics, S2 state multiline spectra, and room temperature electron paramagnetic resonance (EPR) signals indicated that nitrite anions bind PS II in two ways: dissociable (loose) and non‐dissociable (tight). The inhibition caused by the dissociable binding was reversible in washed (nitrite‐treated samples washed with nitrite‐free medium) samples, while the inhibition caused by the non‐dissociable binding was irreversible. At 77 K, an increase in absorption cross section of PS I (as inferred from the excitation spectra of Chl a fluorescence) and a decrease in absorption cross section of PS II in nitrite‐treated sample when compared with sample washed with nitrite‐free medium and control sample suggested that nitrite plays a role in regulating the distribution of absorbed excitation energy between the two photosystems. We propose, for the first time, that the removal of loosely bound nitrite leads to migration of light‐harvesting complex II back to the PS II, and thus the mode of binding of nitrite regulates the extent of migration of antenna molecules between the two photosystems.

The Acceptor Side of Photosystem II Is the Initial Target of Nitrite Stress in Synechocystis sp. Strain PCC 6803

“…2), indicating that the primary site of inhibition is localized to PSII rather than PSI or the intersystem electron transport (ET) components. Previous studies demonstrated that nitrite treatment inhibits the electron transport through PSII and stimulates electron flow through PSI by causing redistribution of the absorbed light energy in favor of the PSI (26,28). Therefore, we contend that the PSII electron transfer was damaged more seriously than the wholechain electron transfer and that the difference was possibly due to redistribution of absorbed excitation energy between two photosystems.…”

“…In the presence of excess nitrite, organisms can accumulate toxic levels of NO 2 Ϫ (24)(25)(26). Previous research showed that isolated chloroplasts subjected to high concentrations of nitrite exhibited decreased chlorophyll (Chl) contents, restricted photosynthetic electron transfer rates (27), and redistribution of absorbed excitation energy between the two photosystems (PS) (28).…”

“…Photosystem II (PSII) has long been considered the target of excess nitrite in isolated thylakoid membranes (29,30). Thermoluminescence studies (31) and loss of S 2 state multiline electron paramagnetic resonance (EPR) signal (26,32) in nitrite-treated samples suggest that nitrite acts on the donor side of PSII, most likely at the manganese (Mn) cluster of the oxygenevolving complex (OEC).…”

Differential changes in photosynthetic capacity, 77 K chlorophyll fluorescence and chloroplast ultrastructure between Zn‐efficient and Zn‐inefficient rice genotypes (Oryza sativa) under low zinc stress

“…Considering the low chl a/b ratio in the Zn deficiency stressed leaves, the low Fv/Fm ratio may suggest a high ratio of PS II to PS I reaction centers in Erjiufeng. Similar to Fv/Fm, the Fv/Fo ratio also recorded a rapid decrease in Erjiufeng, which reflected lower efficiency of electron donation to PSII (Skorzynska and Baszynski 2000) and the structural alterations in PS II (Singh et al 2007).…”

“…The Fv/Fm ratio reflects quantum efficiency of primary photochemical reactions (Singh et al 2007). The rapid decrease in the Fv/Fm ratio occurred in the Zn‐deficient leaves of Erjiufeng indicates that this genotype possesses an intrinsic photochemical capacity far below that of controls, i.e., Zn deficiency induced significant impairment on the quantum yield of PS II in Zn‐inefficient Erjiufeng (Govindjee 1995).…”