Chlorophyll a fluorescence parameters as indicators of a particular abiotic stress in rice

The aim of this study was to evaluate the validity of some chlorophyll (Chl) a fluorescence parameters as early indicators of a particular abiotic stress and also to characterize the effect of different abiotic stresses [high light, NaCl, polyethylene glycol (PEG)-induced osmotic stress, and heavy metals] on the electron transport chain of rice (Oryza sativa L.) seedlings. The results clearly revealed that Chl a fluorescence parameters differ between abiotic stress types and also allowed us to select some parameters which were specifically and intensively affected under different abiotic stresses. We observed that the performance index is a common sensitive parameter to evaluate the effect of above four different abiotic stresses in rice seedlings. Certain Chl a fluorescence parameters were significant for a specific stress. The ratio between the rate constants of photochemical and nonphotochemical deactivation of excited Chl molecules (F-V/F-0) was prominently decreasing and the maximum quantum yield of nonphotochemical deexcitation was prominently increasing upon exposure to high light stress. The maximum quantum yield of electron transport and the electron transport from PSII donor side to PSII reaction center was highly reduced under NaCl stress in rice seedlings. Moreover, F-V/F-0 and PSII structure function index were prominently decreasing and the dissipation per cross section was significantly enhancing under PEG stress. The pool size of reduced plastoquinone on the reducing side of PSII [total complementary area between the fluorescence induction curve and maximal chlorophyll fluorescence (F-M)], F-M, and the probability by which electrons move from PSII to PSI acceptor side were significantly decreasing under heavy metal stress.