Salicylic acid enhances sunflower seed germination under Zn2+ stress via involvement in Zn2+ metabolic balance and phytohormone interactions

Zinc (Zn 2+ ) stress is an important abiotic constraint affecting crop seed germination and plant growth. It is vital to exploit and utilize zinc-polluted soil by exploring technologies for promoting seed germination under Zn 2+ stress. This study aims to explore the effects of salicylic acid (SA) and 2-aminoindan-2-phosphonic acid (AIP, SA synthesis inhibitor) on the Zn 2+ stress resistance of sunflower during seed germination. Zn 2+ treatment significantly inhibited seed germination and seedling growth of sunflower. In addition, Zn 2+ treatment increased Zn 2+ and abscisic acid (ABA) contents, while decreased SA and gibberellins (GA) contents of sunflower seeds. Exogenous SA effectively alleviated the inhibition of Zn 2+ stress on sunflower seed germination, promoted endogenous SA anabolism, and increased the expression of zinc transporter-related genes family ( MTP and HMA ), which leading to decreased Zn 2+ accumulation. Moreover, exogenous SA increased GA content and decreased ABA content by regulating the gene expressions of metabolic related enzymes. On the contrary, AIP treatment further aggravated the inhibitory effect of Zn 2+ stress on sunflower seed germination. This study demonstrated that exogenous SA could affect the Zn 2+ metabolic balance in sunflower seeds by regulating the expression of Zn 2+ transport-related gene ( MTP and HMA ), promote the biosynthesis of endogenous SA and GA, inhibit the accumulation of ABA content, and improve the germination ability of sunflower seed under zinc stress.