Spraying S-ABA Can Alleviate the Growth Inhibition of Corn (zea Mays L.) under Water-Deficit Stress

Drought stress (water-deficit stress) is an important abiotic factor affecting the growth and yield of maize, which threatens food security worldwide. S-Abscisic acid (S-ABA) is widely used to alleviate plant stress. The purpose is to study the effects of exogenous applications of the phytohormone S-ABA on drought resistance in varieties of maize seedlings with contrasting susceptibilities to water-deficit stress (“Zhengdan 958” (ZD958), drought tolerant and “Xundan 20” (XD20), drought sensitive) that were grown under severe and moderate levels of water-deficit stress. Effects of different concentrations of S-ABA (5, 15, 25, and 35 mg kg−1) on chlorophyll and photosynthetic parameters, endogenous ABA, malondialdehyde (MDA) and osmotic substance contents, antioxidant enzyme activity, and Asr1 gene expression in maize seedling leaves. The results showed that S-ABA treatment generally improved drought resistance in the two varieties, where the application of 25 mg kg−1 of S-ABA increased photosynthetic characteristics and chlorophyll fluorescence parameters, content of chlorophyll, endogenous hormone ABA, osmotic substances, activity of antioxidant enzymes, and Asr1 gene expression (p < 0.05). S-ABA reduced MDA content. The content of ABA and osmotic substances, antioxidant enzyme activity, and Asr1 gene expression were higher in ZD958 than in XD20 (p < 0.05). Principal component analysis showed the greatest drought resistance in the varieties treated with 25 mg kg−1 of S-ABA. We concluded that the application of exogenous S-ABA may improve water-deficit stress tolerance in maize seedlings, regardless of inherent susceptibility, and ultimately improve yields in this important crop compared to control.