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

Abstract

Zinc (Zn2+) 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 Zn2+ stress. This study aims to explore the effects of salicylic acid (SA) and 2-aminoindan-2-phosphonic acid (AIP, SA synthesis inhibitor) on the Zn2+ stress resistance of sunflower during seed germination. Zn2+ treatment significantly inhibited seed germination and seedling growth of sunflower. In addition, Zn2+ treatment increased Zn2+ and abscisic acid (ABA) contents, while decreased SA and gibberellins (GA) contents of sunflower seeds. Exogenous SA effectively alleviated the inhibition of Zn2+ 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 Zn2+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 Zn2+ stress on sunflower seed germination. This study demonstrated that exogenous SA could affect the Zn2+ metabolic balance in sunflower seeds by regulating the expression of Zn2+ 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.