Alleviation of photoinhibition by calcium supplement in salt-treated Rumex leaves

By analysis of gas exchange and chlorophyll fluorescence, the effects of NaCl treatment and supplemental CaCl2 on photosynthesis, photosystem II (PSII) photochemistry and photoinhibition were investigated in Rumex leaves. Photosynthesis in Rumex leaves was strongly inhibited by 200 mM NaCl treatment. Such inhibition of photosynthesis was ameliorated by CaCl2 supplement. Neither NaCl treatment nor CaCl2 supplement had any significant effects on the PSII primary photochemical reaction in dark-adapted leaves. In light-adapted leaves, however, 200 mM NaCl treatment significantly decreased photochemical quenching (q(p)), efficiency of excitation energy capture by open PSII reaction centers (F-V'/F-M') and quantum yield of PSII electron transport (Phi(PSII)). These decreases in q(p,) F-V'/F-M' and Phi(PSII) were mitigated by CaCl2 supplement with the maximum of its effect appearing at a concentration of 8 mM CaCl2. A similar mitigating effect was shown in 200 mM NaCl-treated Rumex leaves when susceptibility of PSII to photoinhibition was determined under high irradiance. It is suggested that the mitigation of photoinhibition in NaCl-treated leaves is because of the amelioration of inhibition of photosynthesis.