Correlation between reactive oxygen species production and photochemistry of photosystems I and II in Lemna gibba L. plants under salt stress.

tIncreased rate of reactive oxygen species (ROS) is a common plant response to various environmentalstresses. In chloroplast thylakoids, the reaction centers of photosystems I and II are the major generationsite of ROS. In the present study, the changes of chlorophyll a fluorescence parameters, P700 absorptionchange and ROS production (using the fluorescent probe 2,7-dichlorofluorescin diacetate) were inves-tigated in Lemna gibba plants exposed to salt stress (0–400 mM NaCl). Salt stress inhibited PSI and PSIIactivities and resulted in a decrease in overall activity of the electron transport chain while stimulatingROS production. When L. gibba plants were kept into dark condition, NaCl treatment did not showed anysignificant change in ROS formation compared to control. However, NaCl treatment in light conditioninduced a strong increase in ROS formation. The production of ROS at 400 mM NaCl was 2.6 and 10 foldhigher compared to the control respectively after 6 h and 24 h treatment in light. Furthermore, the corre-lation between ROS production and the two photosystems (PSI and PSII) activities in L. gibba plants wasanalyzed. Our data confirmed the correlation between the ROS production and PSII and PSI activities. Weshowed that ROS production was highly correlated to maximal quantum yield of PSII (R2= 0.91) and effi-ciency with which a trapped exciton can move an electron into the electron transport chain (R2= 0.86).While the correlation coefficient (R2) value ROS formation and I/Io 820 nm(measure of redox states ofplastocyanin and P700) was 0.63.