Abstract This study investigated the ameliorating effect of exogenous proline on some physiological responses of salt acclimated and non-acclimated Aloe vera plants against subsequent salt stress (EC 21 dS/m). Compared to control, salinity decreased leaf growth and relative water content (RWC), leaf contents of chlorophyll a, carotenoids, K/Na ratio, photosystem performance index (PIabs), while promoted leaf contents of hydrogen peroxide (H2O2), maloendialdehyde (MDA) and Na, which subsequently induced oxidative stress. However, foliar applied proline was effective in alleviating the deleterious effects of salinity. Maximum amelioration of salt stress by exogenous proline was found only in salt-acclimated plants, which was attributed to the reduced leaf Na accumulation together with enhanced K content. Proline pretreatment improved plant relative water content, which was correlated with enhancement in leaf proline concentration. We showed that application of proline on salt-acclimated stressed plants alleviated the damage to PSII functioning induced by salinity, contributing to the improvement of the oxygen-evolving complex efficiency of PSII (Fv/Fo) and the quantum yield of electron transport (ΦEo). This improvement of PSII activity was achieved by higher carotenoids and phenolic accumulation. Additionally, proline treatment reduced the accumulation of H2O2 and MDA, indicating that proline pretreatment was more effective in lowering oxidative damage in salt-exposed acclimated plants, which was associated with the activation of SOD, CAT and APX enzymes. Thus, proline pretreatment could protect salt acclimated Alo vera plants against subsequent salt stress through improving K/Na ratio and water relations attributes as well as enhancing antioxidant systems, resulting in better photosynthesis under salt stress.

中文翻译：

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外源脯氨酸通过调节光系统 II 效率和抗氧化防御来增强驯化芦荟的耐盐性

摘要 本研究调查了外源脯氨酸对盐驯化和非驯化芦荟植物对后续盐胁迫 (EC 21 dS/m) 的一些生理反应的改善作用。与对照相比，盐度降低了叶片生长和相对含水量 (RWC)、叶绿素 a、类胡萝卜素、钾/钠比、光系统性能指数 (PIabs) 的含量，同时促进了过氧化氢 (H2O2)、丙二醛 (MDA) 的叶片含量) 和 Na，随后诱导氧化应激。然而，叶面喷施脯氨酸可有效减轻盐度的有害影响。仅在盐驯化植物中发现外源脯氨酸对盐胁迫的最大改善，这归因于叶片 Na 积累减少和 K 含量增加。脯氨酸预处理提高了植物的相对含水量，这与叶脯氨酸浓度的提高有关。我们表明，在盐驯化胁迫植物上施用脯氨酸减轻了盐分对 PSII 功能的损害，有助于提高 PSII 的产氧复合效率 (Fv/Fo) 和电子传输的量子产率 (ΦEo) . PSII 活性的这种改善是通过较高的类胡萝卜素和酚类积累实现的。此外，脯氨酸处理减少了 H2O2 和 MDA 的积累，表明脯氨酸预处理在降低盐暴露驯化植物的氧化损伤方面更有效，这与 SOD、CAT 和 APX 酶的激活有关。因此，