Rosmarinic Acid Production and Expression of Tyrosine Aminotransferase Gene in Melissa officinalis Seedlings in Response to Yeast Extract

Effects of yeast extract (YE) (0, 0.05, 0.1, 0.2, 0.5 and 1%) were investigated on rosmarinic acid (RA) accumulation and tyrosine aminotransferase (TAT) gene expression in Melissa officinalis seedlings at different time intervals (4 and 17 hours). Based on the results, only YE concentrations of 0.05%, 0.1%, and 0.2%, for the 17-hour treatment, significantly stimulated RA biosynthesis pathway. At this elicitation time, flavonoid content and TAT gene expression significantly increased by the increase in YE concentration up to 0.2% as compared to the control. The maximum amount for both of them was seen at 0.1% YE treatment, where the RA accumulation was drastically elevated. Furthermore, the aerial parts were improved when root lengths were decreased; this was observed in seedlings that were treated by YE for 30 days. Overall, these observations can be attributed to the oxidative stress induced by YE, as a consequence of its uptake by the plant, as revealed by increasing activities in superoxide dismutase and catalase.