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.
We studied the development of chloroplasts from etioplasts in the cotyledonary leaves of 4-d-old dark-grown cucumber (Cucumis sativus) seedlings after irradiation (20 μmol m-2 s-1). Upon irradiation, the triggering of chlorophyll (Chl) synthesis and accumulation showed a relatively short lag phase. The irradiation of etiolated seedlings initiated the synthesis of apoproteins of pigment-protein complexes. While Chl-protein 2 (CP2) was detected at 6 h after irradiation, CP1 only after 29 h. The appearance and accumulation of some of the apoproteins were monitored by Western-blotting. LHC2 apoprotein was detected after a 6 h-irradiation. The amounts of D1 protein of photosystem (PS) 2 and PsaA/B protein of PS1 were quantitated by ELISA. Further, the thylakoid membrane function during this time period in terms of PS1- and PS2-mediated electron transfer activity and intersystem electron pool size were analyzed. While PS1 activity was detected after 4 h, PS2-mediated O2 evolution was detected only after a 17 h-irradiation. Fv/Fm value of Chl a fluorescence measurements indicated that the photochemical efficiency of these leaves reached its maximum after 29 h of irradiation. The intersystem pool size of cotyledonary leaves was equivalent to that of the control cotyledonary leaves grown for 25 h under continuous irradiation. Thus etioplasts develop into fully functional chloroplasts after approximately 25 h when 4 d-dark grown cucumber seedlings are continuously moderately irradiated. The development of photosynthetic electron transport chain seems to be limited in time at the level of PS2, possibly at the donor side. and K. Bala Krishna ... [et al.].