Abstract: Two indica rice(Oryza sativa L.) materials,Xieqingzao B(heat-sensitive) and 082(heat-tolerant),were used to study the role of brassinolide(BR) in protection of rice seedlings from heat stress.Young seedlings were subjected to higher temperature and sprayed with 0.005 mg/L of BR.Analysis was conducted on the contents of chlorophyll,protein,malondialdehyde(MDA),electrolyte leakage,the activities of peroxidase(POD) and superoxide dismutase(SOD) and their isozymes expression levels in leaves.Under the heat stress treatment,application of BR significantly increased the contents of chlorophyll and protein,the activities of POD and SOD,and reduced the level of MDA and the leakage of electrolyte in the leaves of the heat-sensitive material Xieqingzao B,whereas BR had less effect on those of the heat-tolerant material 082,relatively.The BR treatment enhanced the expression level of POD isozymes in the leaves of both materials.Under the heat stress and BR treatment,the expression of four SOD isozymes were reduced in 082,but the expression of two SOD isozymes A and B were increased in Xieqingzao B.This suggested that BR plays an important role in protection rice seedlings from heat stress through enhancing the activities or expression levels of protective enzymes in the leaves.The materials with various heat-tolerance might differ in the mechanism of response to heat stress with BR application.

Key words: brassinolide, rice seedlings, heat stress, antioxidase, membrane lipid peroxidation

摘要： 以两个籼稻材料082（耐热型）和协青早B（热敏型）为研究对象探讨高温胁迫下油菜素内酯（BR）对水稻秧苗的保护作用。在苗期进行高温和喷施BR处理，观察高温胁迫下BR对叶绿素、蛋白质和MDA含量、电解质外渗率和保护酶（SOD、POD）活性及其同工酶表达等的影响。结果表明，高温胁迫下，喷施BR能明显提高热敏型材料协青早B的叶片叶绿素和蛋白质含量，增加SOD和POD活性,降低叶片MDA含量和电解质外渗率，但对耐热型材料082的影响相对较小。经BR处理后两个材料的POD同工酶谱带表达均明显增强。在高温胁迫下，BR处理减弱了耐热材料082的4条SOD同工酶谱带的表达，但明显增强了热敏感材料协青早B的A、B两同工酶谱带的表达，表明BR能够增强稻苗内活性氧保护酶系统的活性或诱导其表达，能有效减轻高温对秧苗的伤害。BR处理后稻苗对高温的应答机制，在温敏性不同的材料间存在差异。

关键词: 油菜素内酯, 水稻幼苗, 高温胁迫, 抗氧化酶, 膜脂过氧化作用