Abstract:

【Objective】 The effects of CaCl2 on photosynthesis and antioxidative enzyme activities in tobacco under high temperature stress were investigated to reveal the mechanism of external Ca2+ enhances the thermotolerance of tobacco plants.【Method】 The K326 tobacco plants were sprayed with different concentrations (0, 10, 20, 30) of CaCl2 for four days, at the fifth day exposed to 43℃ for 2 hours, then returned to normal growth condition for one day recovery. Photosynthetic rate, chlorophyll fluorescence transients (OJIP), MDA content, H2O2 content and the activities of antioxidative enzymes were studied during the process. 【Result】 Under heat stress, CaCl2 pretreatment greatly reduced the decrease in net photosynthesis rate (Pn) and maximum photochemical efficiency of PSⅡ(Fv/Fm). Moreover,it alleviated the damage of heat stress to electron transportation of PSII center and oxygen-evolving complex, so that the PSII could maintain high activity. CaCl2 pretreatment also greatly enhanced the activities of SOD, POD, CAT and APX, reduced the accumulation of H2O2, and thus, the active oxygen species were scavenged efficiently; the accumulation of final product of membrane lipid peroxidation (MDA) greatly decreased. The tobacco plants pretreated with 20 mmol?L-1 CaCl2 maintained the highest antioxidant enzymes activities and photosynthetic ability. 【Conclusion】 CaCl2 pretreatment alleviated the heat stress damage to PSII center and oxygen evolving complex via enhancing the antioxidant enzymes activities, reducing the accumulation of H2O2 and protecting the membrane from peroxidation. Exogenous CaCl2 application enhanced thermotolerance of tobacco plants under high temperature stress.

Key words: tobacco, high temperature stress, CaCl2, photosynthesis, antioxidative enzyme