热锻炼对杜鹃花耐热性的影响

为探究热锻炼对杜鹃花Rhododendron耐热性的影响及作用机制，对经30℃热锻炼的杜鹃花品种‘状元红’Rhododendron ‘Zhuangyuan Hong’在不同热胁迫下（38℃，42℃）的叶片解剖结构、光合作用及生理生化特征变化进行分析。结果显示:在热胁迫下，经过热锻炼的叶片与未经热锻炼的叶片相比，解剖结构受损较轻，能保持较高的栅海比和结构紧密度（R_CT）；净光合速率（P_n）得到了提高，胞间二氧化碳摩尔分数（C_i）降低；过氧化氢（H₂O₂）及丙二醛（MDA）质量摩尔浓度均减少，渗透调节物质质量分数均减少；超氧化物歧化酶（SOD）活性降低，而过氧化物酶（POD）及过氧化氢酶（CAT）活性在38℃高温下均降低，在42℃高温下均增高。试验表明，热锻炼处理能较好地保持叶片结构的稳定，并能提高叶片光合速率，同时减轻细胞受损程度，一定程度上提高了杜鹃花品种‘状元红’植株的耐热性。

Heat-resistance of Rhododendron with a heat acclimation pretreatment

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 R_CT also was increased. Leaves with heat acclimation maintained a significantly higher net photosynthetic rate(P_n) and lower intercellular CO₂ concentration(C_i), 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.