The role of melatonin treatments on improving plant tolerance against drought stress is clear, while its special role and influences are poorly investigated. Thus, the effect of external treatment with different concentrations (2.5, 5.0 and 7.5 mM) of melatonin on two varieties of flax plant (Letwania-9 and Sakha-2) growth, some biochemical aspects and yield under normal [100% water irrigation requirements (WIR)] and drought stress conditions (75% and 50% WIR) in sandy soil were investigated in this study. Drought stress decreased significantly different growth parameters, photosynthetic pigments, yield and yield components of the two studied flax varieties. While, it increased significantly phenolic contents, total soluble sugars (TSS), proline and free amino acids as well as some antioxidant enzymes (superoxide dismutase, catalase, peroxidase and polyphenol oxidase). Meanwhile, external treatment of melatonin (2.5, 5.0 and 7.5 mM) increased significantly different growth and yield parameters as well as the studied biochemical and physiological aspects under 100% WIR. Also, melatonin treatment could alleviate the adverse effects of drought stress and increased significantly growth parameters, yield and quality of the two varieties of flax plant via improving photosynthetic pigments, indole acetic acid, phenolic, TSS, proline free amino acids contents and antioxidant enzyme systems, as compared with their corresponding untreated controls. Foliar treatment of 5.0 mM melatonin showed the greatest growth, the studied biochemical aspects and yield quantity and quality of Letwania-9 and Sakha-2 varieties of flax plants either at normal irrigation or under stress conditions. Finally we can conclude that, melatonin treatment improved and alleviated the reduced effect of drought stress on growth and yield of two flax varieties through enhancing photosynthetic pigment, osmoptrotectants and antioxidant enzyme systems. 5 mM was the most effective concentration.

中文翻译：

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沙土下褪黑激素叶面处理缓解两个亚麻品种的干旱胁迫。


褪黑素处理在提高植物对干旱胁迫的耐受性方面的作用是显而易见的，但其特殊作用和影响却很少被研究。因此，不同浓度（2.5、5.0 和 7.5 mM）褪黑激素的外部处理对两个亚麻品种（Letwania-9 和 Sakha-2）生长、某些生化方面和正常[100% 水灌溉要求下的产量]的影响本研究对沙土中的干旱胁迫条件（75% 和 50% WIR）进行了调查。干旱胁迫显着降低了两个研究亚麻品种的不同生长参数、光合色素、产量和产量组成。同时，它显着增加了酚类含量、总可溶性糖（TSS）、脯氨酸和游离氨基酸以及一些抗氧化酶（超氧化物歧化酶、过氧化氢酶、过氧化物酶和多酚氧化酶）。同时，褪黑激素（2.5、5.0 和 7.5 mM）的外部处理显着增加了不同的生长和产量参数以及在 100% WIR 下研究的生化和生理方面。此外，褪黑素处理可以通过改善光合色素、吲哚乙酸、酚类、TSS、脯氨酸游离氨基酸含量和抗氧化酶系统，减轻干旱胁迫的不利影响，显着提高两个亚麻品种的生长参数、产量和品质。 ，与相应的未处理对照相比。无论是在正常灌溉还是在胁迫条件下，5.0 mM 褪黑素叶面处理显示出 Letwania-9 和 Sakha-2 亚麻品种的最大生长、所研究的生化方面以及产量和质量。 最后我们可以得出结论，褪黑素处理通过增强光合色素、渗透保护剂和抗氧化酶系统，改善和缓解了干旱胁迫对两个亚麻品种生长和产量的影响。 5 mM 是最有效的浓度。