The beneficial effects of 5-aminolevulinic acid (ALA) on abiotic stress have been demonstrated in several plant species. However, little is known about the signal transduction pathways triggered by ALA in the photooxidative stress response. In this study, we investigated the effects of ALA on methyl viologen (MV)-induced photooxidative stress tolerance in detached pear leaves (Pyrus ussuriensis). Furthermore, we also examined the involvement of NADPH oxidase (RBOH)-mediated H₂O₂ as a signaling molecule in ALA-induced photooxidative stress tolerance. Our results showed that exogenous ALA alleviated the observed decreases in chlorophyll content and maximum potential photosystem II efficiency under MV-induced stress. Exogenous ALA also effectively reduced MV-induced oxidative damage and enhanced the activities of antioxidative enzymes (SOD and CAT). In situ determination of reactive oxygen species revealed that ALA induced H₂O₂ production in the pear leaves. Importantly, ALA-induced tolerance was abolished by an RBOH inhibitor. Further investigation revealed that the transient overexpression of RBOHF in tobacco leaves alleviated MV-induced damage by enhancing the activities of SOD and CAT. This study provides new insights into the mechanisms by which ALA improves photooxidative tolerance in pear leaves.

5-氨基乙酰丙酸 (ALA) 对非生物胁迫的有益作用已在几种植物物种中得到证实。然而，关于光氧化应激反应中由 ALA 触发的信号转导途径知之甚少。在这项研究中，我们研究了 ALA 对分离的梨叶（Pyrus ussuriensis）中甲基紫精（MV）诱导的光氧化应激耐受性的影响。此外，我们还检查了 NADPH 氧化酶 (RBOH) 介导的 H ₂ O _{2 的参与}作为 ALA 诱导的光氧化应激耐受中的信号分子。我们的结果表明，外源 ALA 减轻了观察到的叶绿素含量下降和 MV 诱导的压力下最大潜在光系统 II 效率。外源性 ALA 还有效减少了 MV 诱导的氧化损伤并增强了抗氧化酶（SOD 和 CAT）的活性。活性氧的原位测定表明，ALA 诱导梨叶中H ₂ O _{2 的}产生。重要的是，RBOH 抑制剂消除了 ALA 诱导的耐受性。进一步的研究表明，RBOHF的瞬时过表达在烟叶中通过增强 SOD 和 CAT 的活性减轻了 MV 诱导的损伤。这项研究为 ALA 提高梨叶光氧化耐受性的机制提供了新的见解。