Dhaubhadel S, Chaudhary S, Dobinson K F, Krishna P
Department of Plant Sciences, University of Western Ontario, London, Canada.
Plant Mol Biol. 1999 May;40(2):333-42. doi: 10.1023/a:1006283015582.
Brassinosteroids are plant growth-promoting compounds that exhibit structural similarities to animal steroid hormones. Recent studies have indicated that brassinosteroids are essential for proper plant development. In addition to a role in development, several lines of evidence suggest that brassinosteroids exert anti-stress effects on plants. However, the mechanism by which they modulate plant stress responses is not understood. We show here that Brassica napus and tomato seedlings grown in the presence of 24-epibrassinolide (EBR) are significantly more tolerant to a lethal heat treatment than are control seedlings grown in the absence of the compound. Since a preconditioning treatment of seedlings was not required to observe this effect, we conclude that EBR treatment increases the basic thermotolerance of seedlings. An analysis of heat shock proteins (HSPs) in B. napus seedlings by western blot analysis indicated that the HSPs did not preferentially accumulate in EBR-treated seedlings at the control temperature. However, after heat stress, HSP accumulation was higher in EBR-treated than in untreated seedlings. The results of the present study provide the first direct evidence for EBR-induced expression of HSPs. The higher accumulation of HSPs in EBR-treated seedlings raises the possibility that HSPs contribute, at least in part, to thermotolerance in EBR-treated seedlings. A search for factors other than HSPs, which may directly or indirectly contribute to brassinosteroid-mediated increase in thermotolerance, is underway.
油菜素甾醇是一类促进植物生长的化合物，其结构与动物甾体激素相似。最近的研究表明，油菜素甾醇对植物的正常发育至关重要。除了在发育过程中发挥作用外，多项证据表明油菜素甾醇对植物具有抗逆作用。然而，它们调节植物应激反应的机制尚不清楚。我们在此表明，在24-表油菜素内酯（EBR）存在下生长的甘蓝型油菜和番茄幼苗，比在无该化合物条件下生长的对照幼苗对致死性热处理的耐受性显著更高。由于观察到这种效应不需要对幼苗进行预处理，我们得出结论，EBR处理提高了幼苗的基础耐热性。通过蛋白质免疫印迹分析对甘蓝型油菜幼苗中的热休克蛋白（HSP）进行分析表明，在对照温度下，HSP在经EBR处理的幼苗中不会优先积累。然而，热胁迫后，经EBR处理的幼苗中HSP的积累高于未处理的幼苗。本研究结果为EBR诱导HSP表达提供了首个直接证据。经EBR处理的幼苗中HSP的较高积累增加了HSP至少部分促成经EBR处理幼苗耐热性的可能性。目前正在寻找除HSP之外可能直接或间接促成油菜素甾醇介导的耐热性增加的因素。
