Biosynthesis of phenylpropanoids and their protective effect against heavy metals in nitrogen-fixing black locust (Robinia pseudoacacia)

Abstract

Purpose: To examine the effect of various heavy metals (HMs) on phenylpropanoid pathway compounds in Robinia pseudoacacia. Methods: A series of pot culture experiments were performed to understand how the metabolic profile of phenylpropanoid compounds were affected by various HMs, such as redox-active HMs (AgNO3 and CuCl2), and non-redox-active HMs (HgCl2). Phenylpropanoid compound level was evaluated by high performance liquid chromatography. Results: The total phenylpropanoid level in leaves increased significantly in all the treated groups when compared to that in the untreated group (p < 0.05). However, a significant effect on the total phenylpropanoid levels was only found for redox-active HMs (p < 0.05), whereas non-redox-active HMs showed less accumulation. Chlorogenic acid and rutin were the two major phenylpropanoid compounds found after the plants were subjected to redox and non-redox-active HMs stress. However, when compared to these two compounds, the levels of catechin hydrate, epicatechin, p-coumaric acid, kaempferol, and quercetin were lower. Caffeic acid level was significantly decreased in both redox and non-redox-active HMs when compared to that in the control (p < 0.05). In addition, trans-cinnamic acid accumulation was altered based on the types and concentration of HMs. Conclusion: Phenylpropanoid metabolic pathway participated in the HM tolerance process for the protection of R. pseudoacacia from oxidative damage caused by HMs, thus allowing the species to grow in highly HMs-contaminated areas.