Phenotypic, physiological, and molecular response of Loropetalum chinense var. rubrum under different light quality treatments based on leaf color changes

Light quality is a vital environmental signal used to trigger growth and to develop structural differentiation in plants, and it influences morphological, physiological, and biochemical metabolites. In previous studies, different light qualities were found to regulate the synthesis of anthocyanin. However, the mechanism of the synthesis and accumulation of anthocyanins in leaves in response to light quality remains unclear. In this study, the Loropetalum chinense var. rubrum "Xiangnong Fendai" plant was treated with white light (WL), blue light (BL), ultraviolet-A light (UL), and blue light plus ultraviolet-A light (BL + UL), respectively. Under BL, the leaves were described as increasing in redness from "olive green" to "reddish-brown". The chlorophyll, carotenoid, anthocyanin, and total flavonoid content were significantly higher at 7 d than at 0 d. In addition, BL treatment also significantly increased the accumulation of soluble sugar and soluble protein. In contrast to BL, ultraviolet-A light increased the malondialdehyde (MDA) content and the activities of three antioxidant enzymes in the leaves, including catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD), in varying degrees over time. Moreover, we also found that the CRY-like gene, HY5-like gene, BBX-like gene, MYB-like gene, CHS-like gene, DFR-like gene, ANS-like gene, and UFGT-like gene were significantly upregulated. Furthermore, the SOD-like, POD-like, and CAT-like gene expressions related to antioxidase synthesis were found under ultraviolet-A light conditions. In summary, BL is more conducive to reddening the leaves of "Xiangnong Fendai" and will not lead to excessive photooxidation. This provides an effective ecological strategy for light-induced leaf-color changes, thereby promoting the ornamental and economic value of L. chinense var. rubrum.Published versionThe work was funded the Innovation training program for Open Project of Horticulture Discipline of Hunan Agricultural University: 2021YYXK001; The Forestry Science and Technology Innovation Foundation of Hunan Province for Distinguished Young Scholarship: XLKJ202205; Key project of Hunan Provincial Department of Education: 22A0155; The Found of Changsha Municipal Science and Technology Bureau: KQ2202227; Hunan Provincial Natural Science Youth Foundation Project: 2020JJ5264; Hunan Provincial Education Department Teaching reform Project: 2021JGYB101; Hunan Agricultural University Teaching reform research project: XJJG-2020-071; the Hunan Provincial Philosophy and Social Science 579 Achievement Evaluation Committee project: XSP20YBZ123; The Forestry Bureau for Industrialization management of Hunan Province: 2130221