Effects of different hormones on the color of tree peony leaves

Abstract

Background: Anthocyanin and chlorophyll are two compounds responsible for coloration in plants. Plant hormones can influence the accumulation of anthocyanins and chlorophyll. In this study, Paeonia ostii and Paeonia qiui, which exhibit red leaves during their juvenile stage, were selected to explore the effects of different hormones on leaf coloration. Results: Tree peony leaves predominantly contained cyanidin-3,5-O-diglucoside (Cy3G5G) and peonidin-3,5-O-diglucoside (Pn3G5G), with minimal peonidin-3-O-glucoside (Pn3G). Among eight phytohormone treatments, gibberellins (GA3), group maximized anthocyanin accumulation while methyl jasmonate (MeJA) group showed opposite effects. Anthocyanin accumulation was influenced by eight plant hormones, but only MeJA group had a notable effect on chlorophyll production. GA3 group significantly upregulated gibberellin 2-oxidase (GA2ox) expression in two tree peony species, enhancing endogenous GA biosynthesis. Concurrently, GA3 group significantly upregulated the expression of multiple key genes in the anthocyanin biosynthetic pathway in tree peony leaves. Specifically, dihydro flavonol 4-reductase (PoDFR) exhibited the most pronounced upregulation (1.325-fold) in Paeonia ostii leaves, while anthocyanidin synthase (PqANS) showed a remarkable (5.72-fold) increase in expression in Paeonia qiui leaves. MeJA group significantly upregulated the expression of allene oxide synthase (AOS) and allene oxide cyclase (AOC) genes in the jasmonic acid (JA) biosynthesis pathway, consequently enhancing endogenous JA levels in the leaves. High levels of JA stimulated the activation of genes involved in chlorophyll synthesis in plants. However, the expression of most anthocyanin biosynthetic genes in MeJA group was significantly suppressed, with particularly marked downregulation observed in chalcone synthase (CHS) and glucose-flavonoid-3-glucosyltransferase (UFGT). Furthermore, MeJA and GA3 may engage in complex crosstalk with other hormones, potentially exhibiting either synergistic or antagonistic interactions that modulate plant physiological responses. Conclusions: The tree peony leaves treated with GA3, strigolactone analog (rac-GR24), brassinosteroids (BR), and 6-benzyladenine (6-BA) were redder in color, but leaves treated with indole-3-acetic acid (IAA), salicylic acid (SA), abscisic acid (ABA), and MeJA were greener than control (CK) group. This study provides a basis for further research on the mechanism of hormone regulation of leaf color in tree peony.