Maryam Madadkar Haghjou - Department of Biology, Plant Physiology, Faculty of Science, Lorestan University

Oxidant substrates such as H2O2, are able to induce oxidative stress in cells, similar to what occurs in the environmental stresses and cause to decrease in chlorophyll fluorescence (a marker in the evaluation of sensitivity). In this research, two Dunaliella isolates (D-1 & D-2) having different chlorophyll contents (D-1 was included higher chl content) were exposed to the different levels of H2O2 (0.1, 0.1, 0.3 mM) during 24 h. The increase in Fo (minimum fluorescence) was not observed in both species. In contrast, Fm (maximal fluorescence) was increased in both, compared to the controls, but reduced at the higher concentrations. FV/FM (quantum yield of Photosystem II), was significantly increased in D- 2, under 0.3 mM H2O2. Photosynthetic pigments, Chl a, Chl b and β-carotene were increased at both species by 0.1 mM supply but reduced at the higher levels. This can propound a possibility that the lower levels of H2O2 may induce antioxidant system and improve the defense system against the stress. In the species having higher chlorophyll content (D-1), all cells were destroyed after exposure to the highest concentration of H2O2, but the second species, only decreased the number of cells about 40% and the ratio of FV/FM was inversely increased in this species. Overall, these findings showed that there might be a positive correlation between chlorophyll content and the sensitivity of the cells to the oxidants like H2O2

Chlorophyll fluorescence, FV/FM, H2O2,Oxidative stress, Photosynthetic system