Abstract Drought and salinity are the main limiting factors negatively affect plant growth and productivity. Proline is recently reported to play a positive role in plants exposed to various abiotic stresses. A two year field experiment was implemented consecutively to assess the potential effect of exogenously applied proline (1 and 2 mM) under different irrigation water regimes (IWR) (120 %, 100 %, 80 % and 60 % of ETc.) on growth, plant defense system, physio-biochemical attributes, bulb yield and water use efficiency of onion cultivated in saline calcareous soil. Results showed that, exogenously-applied proline significantly enhanced growth as well as, plant water status, photosynthetic efficiency, and osmoprotectants of drought-stressed onion which consequently reflected in increased bulb yield. Treatments of 80 % and 60 % of ETc had increased water use efficiency (WUE) by 32.0 % and 26.5 % respectively, compared to full irrigation (100 % of ETc). The effect of proline was negligible on unstressed plants, but when applied under deficit irrigation (DI) treatments (80 and 60 % of ETc), WUE reached 50 % higher than control. These plants also had a higher content of total soluble sugars but a lower content of proline and amino acids. Exogenous proline application markedly enhanced onion growth traits compared to non-treated plants due to increased cell membrane integrity (MSI) and leaf water content (RWC), also improved photosynthetic efficiency and up-regulated osmoprotectants contents. Results revealed that proline foliar application on onion plants might attenuate drought stress by increasing their sugar content and via improving plant self-defense system. Consequently, combination of DI at 80 % and 1−2 mM proline is highly recommended to attain optimal yield with the opportunity of saving 20−40 % of irrigation water during onion growing season.

中文翻译：

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外源施用脯氨酸通过提高光合作用效率、水分利用效率和上调渗透保护剂来提高干旱胁迫洋葱的生长和生产力

摘要 干旱和盐度是影响植物生长和生产力的主要限制因素。最近有报道称脯氨酸在暴露于各种非生物胁迫的植物中发挥积极作用。连续进行了两年的田间试验，以评估在不同灌溉水制度 (IWR)（ETc 的 120%、100%、80% 和 60%）下外源施用脯氨酸（1 和 2 mM）对生长的潜在影响，在盐渍钙质土壤中栽培洋葱的植物防御系统、理化特性、鳞茎产量和水分利用效率。结果表明，外源施用脯氨酸显着增强了干旱胁迫洋葱的生长以及植物水分状况、光合效率和渗透保护剂，从而反映在鳞茎产量增加上。与完全灌溉（ETc 的 100%）相比，ETc 的 80% 和 60% 的处理分别将水利用效率 (WUE) 提高了 32.0% 和 26.5%。脯氨酸对未受胁迫的植物的影响可以忽略不计，但在亏缺灌溉 (DI) 处理（ETc 的 80% 和 60%）下应用时，WUE 比对照高 50%。这些植物的可溶性总糖含量也较高，但脯氨酸和氨基酸的含量较低。由于细胞膜完整性 (MSI) 和叶含水量 (RWC) 增加，外源脯氨酸应用与未处理植物相比，显着增强了洋葱的生长性状，还提高了光合作用效率和上调渗透保护剂含量。结果表明，在洋葱植物上叶面喷施脯氨酸可能通过增加其糖含量和改善植物自卫系统来减轻干旱胁迫。因此，强烈建议将 80% 的 DI 和 1-2 mM 脯氨酸结合使用，以获得最佳产量，并有机会在洋葱生长季节节省 20-40% 的灌溉用水。