Methyl jasmonate enhances carotenoid accumulation and lignin deposition in carrot taproot

Jasmonates are important plant hormones widely involved in processes such as plant growth and stress responses. However, the effects of jasmonic acid on the growth, development, and quality formation in carrots (Daucus carota L.) are less frequently reported. In this study, treatments of 100 µmol/L methyl jasmonate (MeJA), 200 µmol/L MeJA, and 10 mmol/L sodium diethyldithiocarbamate (DIECA) were established, with water serving as the control group, to investigate the effects of different concentrations of MeJA and its inhibitor DIECA on carrot growth and development, fleshy root structure, and the accumulation of lignin and carotenoids. Compared to the control, MeJA treatment significantly increased the number of xylem vessels in the carrot fleshy root, with thickened cell walls, enhanced lignin-related enzyme activities, and well-developed xylem. Different concentrations of MeJA promoted the accumulation of both lignin and carotenoids in carrots, whereas DIECA treatment did the opposite. Gene expression analysis indicated that MeJA altered the transcript levels of genes in carotenoid and lignin metabolism. The research findings in this paper would provide new insights into jasmonic acid-mediated carrot root development and quality formation.