Induction of benzoic acid 2-hydroxylase and salicylic acid biosynthesis—Modulation by salt stress in rice seedlings

Salicylic acid (SA) is an important signal molecule of the plant defense response and is involved in regulation of the anti-oxidative system. Endogenous SA content is increased by various environmental stresses, including salinity. SA biosynthesis is catalyzed by benzoic acid 2-hydroxylase (BA2H). Therefore, induction and control of BA2H under stress conditions are important for the anti-oxidative system. We studied the induction and inhibition of BA2H in rice seedlings under salt stress. BA2H activity was induced by salinity, suggesting that the increased SA content was caused by activation of BA2H. Moreover, induction of BA2H activity was also caused by other oxidative stresses. As BA2H is a member of the cytochrome P-450 (P450) family, we further investigated the inhibitory effect on BA2H in vitro using various inhibitors of P450. Uniconazole proved to be the most effective inhibitor of BA2H. When rice seedlings were exposed to salt stress and treated with uniconazole in vivo, accumulation of SA was suppressed. These results suggest that inhibition of BA2H can control the endogenous response to salt stress and prevent SA accumulation in rice seedlings under oxidative stress.