Damaging mechanisms of chilling- and salt stress to Arachis hypogaea L. leaves

To investigate damaging mechanisms of chilling and salt stress to peanut (Arachis hypogaea L.) leaves, LuHua 14 was used in the present work upon exposure to chilling temperature (4 degrees C) accompanied by high irradiance (1,200 mu mol m(-2) s(-1)) (CH), salt stress accompanied by high irradiance (1,200 mu mol m-2 s-1) (SH), and high-irradiance stress (1,200 mu mol m(-2) s(-1)) at room temperature (25 degrees C) (NH), respectively. Additionally, plants under low irradiance (100 mu mol m(-2) s(-1)) at room temperature (25 degrees C) were used as control plants (CK). Relative to CK and NH treatments, both the maximal photochemical efficiency of PSII (F(v)/F(m)) and the absorbance at 820 nm decreased greatly in peanut leaves under CH and SH stress, which indicated that severe photoinhibition occurred in peanut leaves under such conditions. Initial fluorescence (F(o)), 1 - q(P) and nonphotochemical quenching (NPQ) in peanut leaves significantly increased under CH-and SH stress. Additionally, the activity of superoxide dismutase (SOD), one of the key enzymes of water-water cycle, decreased greatly, the accumulation of malondialdehyde (MDA) and membrane permeability increased. These results suggested that damages to peanut photosystems might be related to the accumulation of reactive oxygen species (ROS) induced by excess energy, and the water-water cycle could not dissipate energy efficiently under the stress of CH and SH, which caused the accumulation of ROS greatly. CH and SH had similar damaging effects on peanut photosystems, except that CH has more severe effects. All the results showed that CH- and SH stress has similar damaging site and mechanisms in peanut leaves.