Water deficit is the most limiting abiotic stress to plants because it affects several physiological and biochemical processes. Brassinosteroids, including 24-epibrassinolide (EBR), are steroids that regulate growth and positively act on gas exchange. This research aims to determine whether EBR can attenuate the negative effects of water deficit, revealing possible contributions of this steroid on photosynthetic machinery of young Eucalyptus urophylla plants under water deficit. The experiment had a completely randomized factorial design with two water conditions (control and water deficit) and three levels of 24-epibrassinolide (0, 50 and 100 nM EBR). Water deficit caused a decrease in the levels of total chlorophyll and carotenoids, but these photosynthetic pigments increased by 135 and 226%, respectively, in plants sprayed with EBR when compared to the water deficit + 0 nM EBR treatment. Regarding the antioxidant system, 100 nM EBR induced significant increments in SOD (42%), CAT (52%), APX (147%) and POX (204%). Steroid application in E. urophylla plants exposed to water deficit increased the effective quantum yield of the photosystem II photochemistry and electron transport rate. However, interestingly, it decreased the nonphotochemical quenching and relative energy excess at the PSII level, indicating improvements related to photosystem II efficiency. This research revealed that application of 100 nM EBR attenuated the negative effects caused by water deficit, being explained by the positive repercussions on antioxidant enzyme activities, chloroplastic pigments, photosystem II efficiency, electron flux and net photosynthetic rate. This article is protected by copyright. All rights reserved.

中文翻译：

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阐明油菜素类固醇在减轻幼龄桉树植物干旱胁迫中的作用：对氧化还原稳态和光合装置的影响

水分亏缺是对植物影响最大的非生物胁迫，因为它会影响多种生理和生化过程。油菜素类固醇，包括 24-表油菜素内酯 (EBR)，是调节生长和积极作用于气体交换的类固醇。本研究旨在确定 EBR 是否可以减轻缺水的负面影响，揭示这种类固醇对缺水条件下幼年桉树植物光合机制的可能贡献。该实验采用完全随机因子设计，具有两种水条件（对照和缺水）和三个水平的 24-表布拉斯内酯（0、50 和 100 nM EBR）。缺水导致总叶绿素和类胡萝卜素水平下降，但这些光合色素分别增加了 135% 和 226%，与水分亏缺 + 0 nM EBR 处理相比，在用 EBR 喷洒的植物中。关于抗氧化系统，100 nM EBR 导致 SOD (42%)、CAT (52%)、APX (147%) 和 POX (204%) 显着增加。暴露于缺水的 E. urophylla 植物中的类固醇应用增加了光系统 II 光化学和电子传输速率的有效量子产率。然而，有趣的是，它降低了 PSII 水平的非光化学猝灭和相对能量过剩，表明与光系统 II 效率相关的改进。这项研究表明，100 nM EBR 的应用减弱了缺水引起的负面影响，这可以通过对抗氧化酶活性、叶绿体色素、光系统 II 效率、电子通量和净光合速​​率的积极影响来解释。本文受版权保护。版权所有。