Heat stress has negative effects on plant performance, especially in photosynthesis and photoprotection. To withstand heat stress, plants modulate steroid phytohormones, brassinosteroids (BRs). However, their regulation and functions in heat stress acclimation are still poorly understood. Plant growth, photoinhibition, photo-oxidative stress and endogenous contents of hormones (including not only BRs but also abscisic acid, salicylic acid and jasmonic acid) were evaluated during heat stress in Arabidopsis thaliana wild type plants and loss-of-function mutations in either BR biosynthetic or signaling genes. It was found that a defect in BRI1-EMS-SUPPRESSOR 1 (bes1)-mediated BR signaling showed the most sensitive characteristics to heat stress compared to wild type and other BR mutants. Sensitivity was associated with declined PSII photochemistry efficiency (Fv/Fm) together with increased carotenoid, tocopherol and lipid hydroperoxide contents, which evidences higher photoinhibition and photo-oxidative stress in the bes1 mutant under heat stress. Furthermore, the bes1 mutant showed greater contents of abscisic acid (ABA) after one day of exposure to heat stress. However, all heat stress symptoms in the bes1 mutant could be mitigated by the application of 24-epibrassinolide. Therefore, it is concluded that BES1 transcription factor plays a role in plants responses to heat stress, relieving photoinhibition and photo-oxidative stress, but that alternative BR signaling pathways to BES1 may also be effective in heat stress acclimation. Furthermore, this study emphasizes the complex interplay between BR and ABA in the heat acclimation process.

中文翻译：

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BRI1-EMS-SUPPRESSOR 1 (BES1) 介导的油菜素类固醇信号的缺陷增加了拟南芥热应激驯化过程中的光抑制和光氧化应激

热应激对植物性能有负面影响，特别是在光合作用和光保护方面。为了抵御热应激，植物会调节类固醇植物激素、油菜素类固醇 (BRs)。然而，它们在热应激适应中的调节和功能仍然知之甚少。在拟南芥野生型植物的热应激过程中评估了植物生长、光抑制、光氧化应激和激素的内源含量（不仅包括 BRs，还包括脱落酸、水杨酸和茉莉酸）以及两者的功能丧失突变BR 生物合成或信号基因。发现与野生型和其他 BR 突变体相比，BRI1-EMS-SUPPRESSOR 1 (bes1) 介导的 BR 信号传导的缺陷显示出对热应激最敏感的特征。敏感性与 PSII 光化学效率 (Fv/Fm) 下降以及类胡萝卜素、生育酚和脂质过氧化氢含量增加有关，这证明 bes1 突变体在热应激下具有更高的光抑制和光氧化应激。此外，bes1 突变体在暴露于热应激一天后显示出更高的脱落酸 (ABA) 含量。然而，bes1 突变体中的所有热应激症状都可以通过应用 24-表布拉斯内酯来减轻。因此，可以得出结论，BES1 转录因子在植物对热胁迫的反应、缓解光抑制和光氧化胁迫中发挥作用，但 BES1 的替代 BR 信号通路也可能对热胁迫驯化有效。此外，