Salicylic acid promotes seed germination under high salinity by modulating antioxidant activity in Arabidopsis

Findings regarding the role of salicylic acid (SA) in seed germination are somewhat variable, depending on the plant genotypes and experimental conditions used, and thus the molecular mechanisms underlying SA regulation of germination are still unclear. Here, we report that physiological concentrations of SA promote germination under high salinity by modulating antioxidant activity in Arabidopsis. Germination of SA induction deficient 2 (sid2) seeds was hypersensitive to high salinity. While the inhibitory effect of high salinity was exaggerated in the presence of higher concentrations of SA (> 100 mu M), it was significantly reduced in the presence of lower concentrations of SA (< 50 mu M). Under high salinity, the endogenous contents of H2O2 were elevated in wild-type and sid2 seeds but reduced to original concentrations after treatment with 1 mu M SA. Germination of NahG transgenic plants was influenced to a lesser degree by high salinity (NahG is a bacterial gene encoding salicylate hydroxylase that converts salicylic acid to catechol). We found that catechol, an SA degradation product accumulated in the transgenic plants, acts as an antioxidant that compromises the inhibitory effects of high salinity. Our observations indicate that, although SA is not essential for germination under normal growth conditions, it plays a promotive role in seed germination under high salinity by reducing oxidative damage.