Abscisic Acid and Gibberellins Act Antagonistically to Mediate Epigallocatechin-3-Gallate-Retarded Seed Germination and Early Seedling Growth in Tomato

Germination is a crucial event in plant lifecycle mediated by a complex hormonal crosstalk. In this study, we revealed an antagonistic interaction between phytohormone abscisic acid (ABA) and gibberellins in epigallocatechin-3-gallate (EGCG)-retarded germination and early seedling growth in tomato. High concentrations of EGCG (0.5 mM and 1.0 mM) decelerated the seed germination and reduced the germination rate and biomass accumulation in seedlings. EGCG-induced inhibition in seedling growth was associated with oxidative stress and changes in antioxidant enzyme activity. Moreover, EGCG treatment increased the ABA content and decreased the GA3 content, leading to a significant reduction in the ratio of GA3/ABA in a dose-dependent manner. EGCG-induced changes in ABA and GA levels were attributed to the changes in expression levels of genes involved in their metabolism. Either exogenous GA application or endogenous ABA deficiency both alleviated EGCG-induced inhibition in early seedling growth. These results suggest that EGCG inhibits seed germination and early seedling growth by affecting the balance between ABA and GA in tomato. These findings are important to better understand the role of flavonoids in seed germination and their implications in controlling seed dormancy.