The decay of tyrosine cation radical was found to be biphasic at 253 K. The fast phase corresponds to the YZ* component while the slow phase corresponds to the tyrosine D radical (YD*) component. At 253 K, the t1/2 value was ∼28.6 s for the fast phase and ∼190.7 s for the slow phase. The fast phase is attributed to the recombination of charges between YZ* and QA-. The activation energy for the reaction of YZ with QA- between 253 and 293 K was 48 kJ mol-1 in Cl--depleted photosystem 2 (PS2) membranes. Both the decay rate and the amplitude of the PAR-induced signal of YZ* were affected by addition of chloride anion. Change in the decay rate and the amplitude of the PAR-induced signal of YZ* was observed when other anions like Br-, I-, F, HCO3-, NO3-, PO43- were substituted in the Cl--depleted PS2. and A. Jajoo, S. Bharti, A. Kawamori.
Ionic environment is important in regulating photosynthetic reactions. The roles of cations, Mn2+, Mg2+, Ca2+, Na+, and K+ as cofactors in electron transport, energy transfer, phosphorylation, and carbon assimilation are better known than the roles of anions, except for chloride and bicarbonate. Only a limited information exists on the roles and effects of nitri formate, sulphate, and phosphate. In this review, we evaluate and highlight the roles of some specific anions on electron transport as well as on excitation energy transfer processes in photosynthesis. Anions exert significant effects on thyla membrane conformation and membrane fluidity, possibly by redistributing the thylakoid membrane surface charges. The anion/cation induced phase transitions in the hydrophilic domains of the thylakoid membranes are probably responsible for the various structural and co-related functional changes under stress. Anions are also important in regulation of energy distribution between the two photosystems. Anions do not only divert more energy from photosystem (PS) 2 to PS1, but can also reverse the effect of cations on energy distribution in a valence-dependent manner. Anions affect also the structure of the photosynthetic apparatus and excitation energy distribution between the two photosystems. and A. Jajoo, S. Bharti, P. Mohanty.
The aim of our study was to investigate the role of protons in regulating energy distribution between the two photosystems in the thylakoid membranes. Low pH-induced changes were monitored in the presence of a proton blocker, N,N′-dicyclohexylcarbodiimide (DCCD). When thylakoid membranes were suspended in a low-pH reaction mixture and incubated with DCCD, then a decrease in the fluorescence intensity of photosystem II (PSII) was observed, while no change in the intensity of photosystem I (PSI) fluorescence occurred according to the measured fluorescence emission spectra at 77 K. Since low pH induced distribution of energy from PSII to PSI was inhibited in the presence of DCCD, we concluded that pH/proton concentration of the thylakoid membranes plays an important role in regulating the distribution of the absorbed excitation energy between both photosystems., T. Tongra, S. Bharti, A. Jajoo., and Obsahuje bibliografii