DA-6 improves sunflower seed vigor under Al³⁺ stress by regulating Al³⁺ balance and ethylene metabolic

Aluminum (Al³⁺) stress restricts plant seed germination and seedling growth seriously. Here, the sunflower "S175″ variety was used to explore the technique of improving seed vigor under Al³⁺ stress and investigate the effect of diethyl aminoethyl hexanoate (DA-6) on physiological characteristics in sunflower seeds during germination under Al³⁺ stress. The results showed that 3.0 mmol·L^-1 Al³⁺ treatment significantly suppressed the sunflower seed germination and seedling growth. Al³⁺ stress significantly increased Al³⁺ content and secretion rates of citric and malic acids in sunflower seeds during germination. Besides, endogenous ethylene content was increased in Al³⁺-treated seeds. DA-6 serves as a positive signal to regulate the sunflower seed germination under Al³⁺ stress. Moreover, DA-6 enhanced the activities of malic dehydrogenase, citrate synthase, and isocitrate dehydrogenase, up-regulated the expressions of organic acid transport-related genes (ALMT and MATE), resulting in reduced accumulation of Al³⁺. Furthermore, exogenous DA-6 mitigated excessive accumulation of ethylene by decreasing the 1-aminocyclopropane-1-dihydrodipicolinate synthase activity and related-gene expression. However, DA-6 treatment had no effect on abscisic acid or gibberellin metabolism in sunflower seeds under Al³⁺ stress. These results confirmed that DA-6 application enhanced the germination capacity through induction of the synthesis and transport of malic and citric acids, and suppression of the excessive accumulation of endogenous ethylene, thus contributing to alleviate Al³⁺ toxicity in sunflower seeds.