Utilization of fast chlorophyll a fluorescence technique in assessing the salt/ion sensitivity of mung bean and Brassica seedlings

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Effects of NaCl and KCl alone or in combination with CaCl2, Na2SO4 or K2SO4 on fast chlorophyll a (Chl a) fluorescence kinetics of mung bean (Vigna radiata L.) and Brassica (Brassica juncea Coss.) were studied. The concentrations of NaCl and KCl used were 100 mmol/L to 300 mmol/L and the concentration of CaCl2 was 5 mmol/L. Na2SO4 and K2SO4 used were in the range of 50 to 200 mmol/L. Salt treatments were given to 6 d old seedlings and Chl a measurements were taken subsequently for 3 d after the salt treatment. The fast Chl a fluorescence kinetics of mung bean and Brassica seedlings showed no significant change within 3 d of experiments without the addition of salts/ions. The salt/ion treatments significantly affected the Chl a fluorescence kinetics. The initial Chl a fluorescence level (F0) increased after 3 d with NaCl, which was enhanced by the addition of CaCl2. KCl and Na2SO4 or K2SO4 induced an increase in F0 after 1 d of salt treatments. CaCl2 alone and with NaCl or KCl enhanced FM after 1 d of treatment. KCl alone increased FM values after 1 d. However, the maximum Chl a fluorescence level (FM), quantum yield of the primary photochemistry of PS II (ϕPo), quantum yield of electron transport beyond QA− (ϕEo), efficiency that a trapped electron can move further ahead of QA− (ψo) and flux ratio of electron transport (ETo/RC) decreased significantly with NaCl treatments after 3 d of treatment. CaCl2 ameliorated these effects. ABS/RC and DI0/RC was enhanced several folds by NaCl treatments and CaCl2 augmented these effects. Other salts and their combinations also showed enhancement in DI0/RC. However, Na salts showed amplified effects at equimolar concentrations compared to K salts. The most prominent difference in the susceptibility of a system or genotype to different salts or ions is due to the changes of the abundance of active reaction centers per leaf cross-section (RC0/CS0).