Heat-resistance of Rhododendron with a heat acclimation pretreatment

Abstract

The anatomy, photosynthesis, as well as physiological and biochemical characteristics (including the cell membrane, osmotic regulation, and enzymatic antioxidant systems) of leaves were investigated in Rhododendron 'Zhuangyuan Hong' to study the effects of heat acclimation on the thermostability of Rhododendron. Plants were exposed to two heat stress levels (38℃ and 42℃) for 6 days, respectively, with a heat acclimation pretreatment at 30℃ for 6 days. Results for a high temperature treatment showed that compared to leaves without heat acclimation, leaves with heat acclimation had less damage on the anatomy. The ratio of palisade and spongy, tissue was increased significantly and RCT also was increased. Leaves with heat acclimation maintained a significantly higher net photosynthetic rate(Pn) and lower intercellular CO2 concentration(Ci), and had a lower content of hydrogen peroxide (H2O2) and malondialdehyde (MDA), which helped stabilize cell structure. Also, activity of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) were lower at 38℃ with POD and CAT activities being higher at 42℃. This study showed that heat acclimation could maintain a stable leaf structure, could improve the photosynthetic rate, and could reduce the extent of cell damage; hence, to some degree improving thermostability.