Acid rain causes significant damage to rice plants, affecting the photosynthetic machinery and growth. 24-epibrassinolide (EBR) is an organic steroid, which, used at low concentrations, positively regulates plant growth and mitigates deleterious effects related to environmental changes. The aim of this study was to investigate whether exogenous treatment with 24-epibrassinolide can alleviate the negative effects of simulated acid rain (SAR) and the possible tolerance mechanism involved by evaluating chlorophyll fluorescence, gas exchange, the antioxidant system and leaf anatomical variables. The experiment was randomized with four treatments: two simulated acid rain treatments (0 and 0.5 M H 2 SO 4 , described as − SAR and + SAR, respectively) and two concentrations of brassinosteroids (0 and 100 nM EBR, described as − EBR and + EBR, respectively). Our results show that plants exposed to SAR suffered negative interferences; however, EBR-treated plants presented benefits related to chlorophyll fluorescence, alleviation of the photoinhibition in photosystem II and protection against damage caused by the imbalance of reactive oxygen species. Additionally, EBR promoted increases in gas exchange that were clearly linked to stomatal regulation, improving the uptake and distribution of CO 2 in intercellular spaces. This research revealed that EBR attenuated the negative effects of SAR, increasing the activities of superoxide dismutase (12%), catalase (17%), ascorbate peroxidase (17%) and peroxidase (33%), reducing thylakoid membrane damage, as confirmed by increases in chlorophyll and carotenoids. Finally, the effects of EBR observed in plants under SAR demonstrate that this substance positively modulated important anatomical structures linked to leaf protection, increasing trichome density (8%), epicuticular wax (48%) and the aerenchyma area (100%). These results provide evidence that EBR confers tolerance to rice plants exposed to SAR.

中文翻译：

---

24-表油菜素内酯在模拟酸雨下正向调节水稻叶片结构、抗氧化系统和光合机制

酸雨对水稻植株造成重大损害，影响光合机械和生长。24-表布拉西内酯 (EBR) 是一种有机类固醇，在低浓度下使用，可积极调节植物生长并减轻与环境变化相关的有害影响。本研究的目的是通过评估叶绿素荧光、气体交换、抗氧化系统和叶片解剖变量，研究外源性 24-表布拉斯内酯处理是否可以减轻模拟酸雨 (SAR) 的负面影响以及可能的耐受机制。实验随机分为四种处理：两种模拟酸雨处理（0 和 0.5 MH 2 SO 4 ，分别描述为 - SAR 和 + SAR）和两种油菜素类固醇浓度（0 和 100 nM EBR，描述为 - EBR 和 + EBR，分别）。我们的结果表明，暴露于 SAR 的植物受到了负面干扰；然而，EBR 处理的植物表现出与叶绿素荧光、减轻光系统 II 中的光抑制以及防止因活性氧不平衡引起的损害相关的益处。此外，EBR 促进了与气孔调节明显相关的气体交换的增加，改善了细胞间隙中 CO 2 的吸收和分布。这项研究表明，EBR 减弱了 SAR 的负面影响，增加了超氧化物歧化酶 (12%)、过氧化氢酶 (17%)、抗坏血酸过氧化物酶 (17%) 和过氧化物酶 (33%) 的活性，减少了类囊体膜损伤，如叶绿素和类胡萝卜素增加。最后，在 SAR 下在植物中观察到的 EBR 效果表明，这种物质积极调节与叶片保护相关的重要解剖结构，增加毛状体密度 (8%)、表皮蜡质 (48%) 和通气组织面积 (100%)。这些结果提供证据表明 EBR 赋予水稻植物耐受 SAR。