MAIN CONCLUSION Activation of GPX and enhanced NO level play a key role in IBA-mediated enhanced Cd tolerance in young barley roots. Application of exogenous indole-3-acetic acid (IAA) or an IAA precursor improves the tolerance of plants to heavy metals. However, the physiology of these tolerance mechanisms remains largely unknown. Therefore, we studied the priming effect of indole-3-butyric acid (IBA), an IAA precursor, on mild and severe cadmium (Cd) stress-induced responses in roots of young barley seedlings. IBA, similarly to mild Cd stress, significantly increased the glutathione peroxidase (GPX) activity in the apexes of barley roots, which remained elevated after the IBA pretreatment as well. IBA pretreatment-evoked high nitric oxide generation in roots effectively reduced the high superoxide level under the severe Cd stress, leading to less toxic peroxynitrite accumulation accompanied by markedly reduced Cd-induced cell death. On the other hand, the IBA-evoked changes in IAA homeostasis resulted in root growth reorientation from longitudinal elongation to radial swelling. However, the application of an IAA signaling inhibitor, following the activation of defense responses by IBA, was able to promote root growth even at high concentrations of Cd. Based on the results, it can be concluded that the application of IBA, as an effective activator of Cd tolerance mechanisms in young barley roots, and the subsequent use of an IAA signaling inhibitor for the inhibition of root morphogenic responses induced by altered auxin metabolism, results in a high degree of root Cd tolerance, helping it to withstand even the transient exposure to lethal Cd concentration without the absolute inhibition of root growth.

中文翻译：

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Indole-3-butyric acid 引发通过 NO 生成和增强谷胱甘肽过氧化物酶活性降低大麦根尖的镉毒性

主要结论 GPX 的激活和 NO 水平的提高在 IBA 介导的增强的大麦幼根对镉的耐受性中起关键作用。应用外源吲哚-3-乙酸 (IAA) 或 IAA 前体可提高植物对重金属的耐受性。然而，这些耐受机制的生理学仍然很大程度上未知。因此，我们研究了 IAA 前体 indole-3-butyric acid (IBA) 对大麦幼苗根部轻度和重度镉 (Cd) 胁迫诱导反应的引发作用。IBA 与轻度 Cd 胁迫相似，显着增加了大麦根尖中的谷胱甘肽过氧化物酶 (GPX) 活性，在 IBA 预处理后也保持升高。IBA预处理诱发根系高一氧化氮生成有效降低了严重Cd胁迫下的高超氧化物水平，导致毒性较低的过氧亚硝酸盐积累伴随着显着减少的镉诱导的细胞死亡。另一方面，IBA 诱发的 IAA 稳态变化导致根生长重新定向，从纵向伸长到径向膨胀。然而，IAA 信号抑制剂的应用，在 IBA 激活防御反应后，即使在高浓度 Cd 下也能够促进根系生长。基于这些结果，可以得出结论，IBA 作为大麦幼根耐镉机制的有效激活剂，以及随后使用 IAA 信号抑制剂来抑制由改变的生长素代谢引起的根形态发生反应，导致高度的根镉耐受性，