The objective of this study was to evaluate the ability of the phytohormone S-abscisic acid (S-ABA) to protect maize seedlings grown under drought stress and to measure their increased drought tolerance. The maize hybrids ‘Zhengdan 958’ (ZD958; drought tolerant) and ‘Xundan 20’ (XD20; drought sensitive) were treated with nutrient solutions of different concentrations (1, 2, 4, 8, and 10 mg/kg) of S-ABA under polyethylene glycol (PEG, 15% w/v, MW 6000) simulated drought stress. Optimal concentrations of S-ABA were designed to be sprayed onto the leaves of seedlings, and their effect on endogenous ABA, malondialdehyde (MDA), osmotic substances, antioxidant enzyme activities, and Asr1 gene expression in seedlings were studied. Results indicated that, under drought stress, S-ABA treatment significantly improved maize seed germination rate (GR), germination energy (GE), and seedling biomass (p < 0.05). After spraying 4 mg/kg S-ABA onto leaves, the endogenous hormone ABA, osmotic substances, antioxidant enzyme activities, and expressive quantity of the Asr1 gene were extended and MDA content dropped significantly (p < 0.05). Moreover, ZD 958 endogenous ABA content, osmotic substances content, antioxidant enzyme activity and Asr1 gene expressive quantity were higher than that of XD 20 (p < 0.05). In conclusion, S-ABA treatment increased the content of endogenous ABA, induced an increase in antioxidant enzyme activity and Asr1 gene expression level, reduced the oxidative damage caused by drought to maize leaves, and improved the adaptability of maize seedlings to withstand drought stress. The promoting effect of S-ABA on the drought-tolerant variety ZD 958 was more obvious (p < 0.05). These results serve as a reference for the use of S-ABA in mitigating drought stress in maize.

中文翻译：

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S-脱落酸（S-ABA）对干旱胁迫下玉米种子萌发、幼苗生长及Asr1基因表达的影响

本研究的目的是评估植物激素 S-脱落酸 (S-ABA) 保护在干旱胁迫下生长的玉米幼苗的能力，并测量它们增加的耐旱性。用不同浓度（1、2、4、8 和 10 mg/kg）的 S- 营养液处理玉米杂交种“正单 958”（ZD958；耐旱）和“寻单 20”（XD20；干旱敏感）聚乙二醇 (PEG, 15% w/v, MW 6000) 下的 ABA 模拟干旱胁迫。设计了最佳浓度的S-ABA喷洒到幼苗叶片上，研究了它们对幼苗内源性ABA、丙二醛(MDA)、渗透物质、抗氧化酶活性和Asr1基因表达的影响。结果表明，在干旱胁迫下，S-ABA处理显着提高了玉米种子发芽率（GR），发芽能量 (GE) 和幼苗生物量 (p < 0.05)。叶片喷施4 mg/kg S-ABA后，内源性激素ABA、渗透物质、抗氧化酶活性和Asr1基因表达量增加，MDA含量显着下降（p < 0.05）。此外，ZD 958内源ABA含量、渗透物质含量、抗氧化酶活性和Asr1基因表达量均高于XD 20（p < 0.05）。综上所述，S-ABA处理增加了内源ABA含量，诱导抗氧化酶活性和Asr1基因表达水平升高，减轻了干旱对玉米叶片的氧化损伤，提高了玉米幼苗对干旱胁迫的适应能力。S-ABA对耐旱品种ZD 958的促生作用更为明显（p < 0.05）。这些结果可作为使用 S-ABA 缓解玉米干旱胁迫的参考。