Effect of endophyte infection on chlorophyll a fluorescence in salinity stressed rice

We have earlier reported that the endophyte infection can enhance photosynthetic capacity and antioxidant enzyme activities in rice exposed to salinity stress. Now, the changes in primary photochemistry of photosystem (PS) II induced by Na2CO3 stress in endophyte-infected (E+) and endophyte-uninfected (E-) rice seedlings were studied using chlorophyll a fluorescence (OJIP-test). Performance indices (PIABS and PITotal) of E- and E+ rice seedlings revealed the inhibitory effects of Na2CO3 on PS II connectivity (occurrence of an L-band), oxygen evolving complex (occurrence of a K-band), and on the J step of the induction curves, associated with an inhibition of electron transport from plastoquinone A (QA) to plastoquinone B (QB). In E+ seedlings, Na2CO3 effects on L and K bands were much smaller, or even negligible, and also there was no pronounced effect on the J step. Furthermore, the OJIP parameters indicated that 20 mM Na2CO3 had a greater influence on the photosystem (PS) II electron transport chain than did the 10 mM Na2CO3, and that changes were greater in E- than in E+. Endophyte infection was therefore deemed to enhance the photosynthetic mechanism of Oryza sativa exposed to salinity stress.