Application of exogenous glycine betaine (GB) and exogenous salicylic acid (SA) mitigates the adverse effects of salinity. Foliar spraying with exogenous GB or SA alleviates salt stress in plants by increasing leaf gas exchange and stimulating antioxidant enzyme activity. The effects of foliar application of exogenous GB and SA on the physiology and biochemistry of cotton seedlings subjected to salt stress remain unclear. Results showed that salt stress of 150 mM NaCl significantly reduced leaf gas exchange and chlorophyll fluorescence and decreased photosynthetic pigment quantities and leaf relative water content. Foliar spray concentrations of 5.0 mM exogenous GB and 1.0 mM exogenous SA promoted gas exchange and fluorescence in cotton seedlings, increased quantities of chlorophyll pigments, and stimulated the antioxidant enzyme activity. The foliar spray also increased leaf relative water content and endogenous GB and SA content in comparison with the salt-stressed only control. Despite the salt-induced increase in antioxidant enzyme content, exogenous GB and SA in experimental concentrations significantly increased the activity of glutathione reductase, ascorbate peroxidase, superoxide dismutase, catalase and peroxidase, and decreased malondialdehyde content under salt stress. Across all experimental foliar spray GB and SA concentrations, the photochemical efficiency of photosystem II (FV/FM) reached a peak at a concentration of 5.0 mM GB. The net photosynthetic rate (Pn) and FV/FM were positively correlated with chlorophyll a and chlorophyll b content in response to foliar spraying of exogenous GB and SA under salt stress. We concluded, from our results, that concentrations of 5.0 mM GB or 1.0 mM SA are optimal choices for mitigating NaCl-induced damage in cotton seedlings because they promote leaf photosynthesis, increase quantities of photosynthetic pigments, and stimulate antioxidant enzyme activity. Among, 5.0 mM GB and 1.0 mM SA, the best performance in enhancing endogenous GB and SA concentrations was obtained with the foliar application of 1.0 mM SA under salt stress.

中文翻译：

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NaCl胁迫棉（Gossypium hirsutum L.）幼苗叶片气体交换属性，光合色素和抗氧化酶对外源甘氨酸甜菜碱和水杨酸的响应。

外源甘氨酸甜菜碱（GB）和外源水杨酸（SA）的应用减轻了盐度的不利影响。叶面喷施外源GB或SA可以增加叶片气体交换并刺激抗氧化酶的活性，从而减轻植物的盐胁迫。叶面施用外源GB和SA对盐胁迫下棉苗生理生化的影响尚不清楚。结果表明，150 mM NaCl的盐胁迫显着减少了叶片气体交换和叶绿素荧光，并降低了光合色素的量和叶片的相对含水量。叶面喷施浓度为5.0 mM的外源GB和1.0 mM的外源SA促进了棉苗的气体交换和荧光，增加了叶绿素色素的含量，并刺激了抗氧化酶的活性。与仅盐胁迫的对照相比，叶面喷雾还增加了叶片的相对水分含量以及内源性GB和SA含量。尽管盐诱导的抗氧化酶含量增加，但实验浓度的外源GB和SA显着提高了谷胱甘肽还原酶，抗坏血酸过氧化物酶，超氧化物歧化酶，过氧化氢酶和过氧化物酶的活性，并降低了盐胁迫下的丙二醛含量。在所有实验性叶面喷雾GB和SA浓度下，光系统II（FV / FM）的光化学效率在5.0 mM GB的浓度下达到峰值。盐胁迫下外源GB和SA叶面喷施后，净光合速率（Pn）和FV / FM与叶绿素a和叶绿素b含量呈正相关。我们从结果得出结论，5.0 mM GB或1.0 mM SA的浓度是减轻NaCl诱导的棉花幼苗损伤的最佳选择，因为它们可以促进叶片的光合作用，增加光合色素的含量并刺激抗氧化酶的活性。在5.0 mM GB和1.0 mM SA中，通过在盐胁迫下叶面施用1.0 mM SA获得了增强内源性GB和SA浓度的最佳性能。