DOES LUTEIN PLAY A KEY ROLE IN THE PROTECTION OF PHOTOSYNTHETIC APPARATUS IN ARABIDOPSIS UNDER SEVERE OXIDATIVE STRESS?

Many environmental stresses result in increased generation of reactive oxygen species (ROS), such as superoxide (center dot O-2(-)), hydrogen peroxide (H2O2), and hydroxyl radical (center dot OH), in plant cells. A mild or moderate stress induces a significant increase in the generation of center dot O-2(-) and H2O2 and a severe stress induces a significant increase in the generation of center dot OH. The three ROS: center dot O-2(-), H2O2 and center dot OH were used to treat leaf discs of the wild type (WT), the npq1 mutant lacking zeaxanthin and the lut2 mutant lacking lutein in Arabidopsis by chlorophyll fluorescence imaging to test our previous hypothesis that lutein might play an important photoprotective role under severe stress. During the center dot O-2(-) and H2O2-treatment under light, F-v/F-m, Phi(PSII), ETR, qP and NPQ exhibited the sequence of sensitivity to ROS in the leaves of the three phenotypes: npq1 > lut2 > WT. However, during the center dot OH-treatment under light, these chlorophyll parameters exhibited another different sequence: lut2 > npq1 > WT. Thus, it can be concluded that xanthophyll cycle plays a key role under mild and moderate stress but lutein plays a key role under severe stress. These results provided more experimental evidence to support our previous hypothesis.