Effects of trace elements on the expression of LjHCT and LjC3H1 for chlorogenic acid synthesis in Lonicera japonica Thunb.

Chlorogenic acid is the main chemical constituent of Lonicera japonica Thunb., and is responsible for various pharmacological activities. Therefore, increases in the chlorogenic acid content in L. japonica flowers is economically and medically important. This study aimed to characterize the effects of applying three micro-elements (Fe, B and Mo) on hydroxycinnamoyl-CoA shikimate/quinate hydroxycinnamoyl transferase (LjHCT) and p-coumaroyl-shikimate 3'-hydroxylase (LjC3H1) genes in L. japonica. Results showed that high Fe concentration had an obvious inhibitory effect on LjHCT gene expression, whereas low and moderate concentrations promoted LjHCT gene expression. With the increase in B and Mo concentrations, the expression of LjHCT also increased significantly. Low Fe concentration promoted LjC3H1 gene expression, whereas high Fe concentration exhibited an inhibitory effect. The effect of B on LjC3H1 expression was not obvious, but high Mo concentration promoted LjC3H1 gene expression. These results showed that chlorogenic acid biosynthesis and accumulation increased with increasing LjHCT and LjC3H1 expressions, which were two key enzymes in the synthesis of chlorogenic acid, and Fe, B and Mo concentrations had significant effects on LjHCT and LjC3H1 expression. Application of moderate or low concentrations of Fe, high or moderate concentrations of Mo, and high or moderate concentrations of B significantly increased the accumulation of chlorogenic acid in L. japonica flowers; however, the application of high concentrations of Fe significantly decreased accumulation. This study provides research-based data for improving the cultivation of L. japonica by increasing the use of trace element fertilizer.