Heat stress is found to be a detrimental factor for growth and development of alfalfa (Medicago sativa L.) which is tremendously invaluable forage due to its high feed value and yield potential. Salicylic acid (SA) has been reported to play a pivotal role in the regulation of plants biotic and abiotic stress response. However, the role of exogenous SA in protecting alfalfa from heat-induced damage has rarely been studied. In this study, four-week-old alfalfa seedlings were treated with 0.25 mM or 0.5 mM SA five days prior to high stress treatment (three day), and various growth and physiological traits were measured. The results showed that exogenous SA pretreatment could improve leaf morphology, plant height, biomass, chlorophyll content, and photosynthetic efficiency of alfalfa under heat stress. Meanwhile, SA could alleviate heat-induced membrane damage by reducing electrolyte leakage (EL) and malondialdehyde (MDA) content, and regulate the activities of antioxidant enzymes including catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD). The results revealed that exogenous SA application enhanced alfalfa heat tolerance by modulating various morphological and physiological characteristics under heat stress, with more prominent effect at lower concentration (0.25 mM). Overall, this study provides fundamental insights into the SA-mediated physiological adaptation of alfalfa plants to heat stress, which could have useful implication in managing other plants which are suffering global warming.

中文翻译：

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外源水杨酸改善了苜蓿（Medicago sativa L.）苜蓿的热应激诱导的伤害，并改善了其生长和光合效率。

发现热胁迫是苜蓿（Medicago sativa L.）的生长和发育的有害因素，由于其高饲料价值和高产潜力，其是非常有价值的饲料。据报道水杨酸（SA）在调节植物生物和非生物胁迫响应中起着关键作用。但是，很少研究外源性SA在保护苜蓿免受热引起的损害中的作用。在这项研究中，在高胁迫处理前三天（三天）用0.25 mM或0.5 mM SA处理四周龄的苜蓿幼苗，并测量了各种生长和生理特性。结果表明，外源SA预处理可以改善高温胁迫下紫花苜蓿的叶片形态，株高，生物量，叶绿素含量和光合效率。与此同时，SA可以通过减少电解质泄漏（EL）和丙二醛（MDA）含量减轻热诱导的膜损伤，并调节抗氧化酶的活性，包括过氧化氢酶（CAT），超氧化物歧化酶（SOD）和过氧化物酶（POD）。结果表明，外源SA的应用通过调节热胁迫下的各种形态和生理特性，提高了苜蓿的耐热性，在较低浓度（0.25 mM）下效果更显着。总体而言，本研究为SA介导的苜蓿植物对热胁迫的生理适应提供了基本的见识，这可能对处理其他遭受全球变暖的植物具有有益的意义。并调节抗氧化酶的活性，包括过氧化氢酶（CAT），超氧化物歧化酶（SOD）和过氧化物酶（POD）。结果表明，外源SA的应用通过调节热胁迫下的各种形态和生理特性，提高了苜蓿的耐热性，在较低浓度（0.25 mM）下效果更显着。总体而言，本研究为SA介导的苜蓿植物对热胁迫的生理适应提供了基本的见识，这可能对处理其他遭受全球变暖的植物具有有益的意义。并调节抗氧化酶的活性，包括过氧化氢酶（CAT），超氧化物歧化酶（SOD）和过氧化物酶（POD）。结果表明，外源SA的应用通过调节热胁迫下的各种形态和生理特性，提高了苜蓿的耐热性，在较低浓度（0.25 mM）下效果更显着。总体而言，本研究为SA介导的苜蓿植物对热胁迫的生理适应提供了基本的见识，这可能对处理其他遭受全球变暖的植物具有有益的意义。在较低浓度（0.25 mM）下效果更显着。总体而言，本研究为SA介导的苜蓿植物对热胁迫的生理适应提供了基本的见识，这可能对处理其他遭受全球变暖的植物具有有益的意义。在较低浓度（0.25 mM）下效果更显着。总体而言，本研究为SA介导的苜蓿植物对热胁迫的生理适应提供了基本的见识，这可能对处理其他遭受全球变暖的植物具有有益的意义。