Cadmium (Cd2+) soil pollution is a global environmental problem caused by the high toxicity of Cd. 24-Epibrassinolide (EBR) is a biodegradable plant steroid involved in response modulation to biotic and abiotic stresses. The aim of this study was to evaluate if the leaf-application of EBR improves the gas exchange and possible repercussions on leaf anatomy in young Eucalyptus urophylla plants exposed to Cd toxicity. The experiment involved six treatments, which included three Cd concentrations (0, 450, and 900 μM) and two EBR concentrations (0 and 100 nM, described as – EBR and + EBR, respectively). Plants exposed to Cd toxicity suffered decreases in leaf anatomical and gas exchange parameters. However, the plants treated with EBR + 900 μM Cd showed an increase of 46%, 40%, and 54% in the net photosynthetic rate, water-use efficiency, and instantaneous carboxylation efficiency, respectively. The EBR application-induced improvements in gas exchange parameters, causing beneficial effects on the photosynthetic apparatus, mainly the effective quantum yield of photosystem II (PSII) photochemistry and electron transport rate. Furthermore, this steroid mitigated the effect of Cd toxicity on leaf anatomical variables, more specifically palisade and spongy parenchyma, which are intrinsically related to stomatal density, and stimulated the net photosynthetic rate of plants.

中文翻译：

---

叶应用 24-表皮油内酯通过调节叶解剖和气体交换减轻幼龄桉树植物的镉毒性

镉 (Cd2+) 土壤污染是由镉的高毒性引起的全球环境问题。24-Epibrassinolide (EBR) 是一种可生物降解的植物类固醇，参与对生物和非生物胁迫的响应调节。本研究的目的是评估叶应用 EBR 是否改善了气体交换以及对幼龄桉树的叶片解剖可能产生的影响暴露于 Cd 毒性的植物。实验涉及六种处理，其中包括三种 Cd 浓度（0、450 和 900 μM）和两种 EBR 浓度（0 和 100 nM，分别描述为 – EBR 和 + EBR）。暴露于 Cd 毒性的植物叶片解剖和气体交换参数下降。然而，用 EBR + 900 μM C​​d 处理的植物的净光合速率、水分利用效率和瞬时羧化效率分别提高了 46%、40% 和 54%。EBR 应用引起气体交换参数的改善，对光合装置产生有益影响，主要是光系统 II (PSII) 光化学的有效量子产率和电子传输速率。此外，这种类固醇减轻了 Cd 毒性对叶片解剖变量的影响，