Exogenous gibberellin enhances secondary xylem development and lignification in carrot taproot

Gibberellins (GAs) are important growth regulators involved in plant development processes. However, limited information is known about the relationship between GA and xylogenesis in carrots. In this study, carrot roots were treated with GA(3). The effects of applied GA(3) on root growth, xylem development, and lignin accumulation were then investigated. Results indicated that GA treatment dose-dependently inhibited carrot root growth. The cell wall significantly thickened in the xylem parenchyma. Autofluorescence analysis with ultraviolet (UV) excitation indicated that these cells became lignified because of long-term GA(3) treatment. Moreover, lignin content increased in the roots, and the transcripts of lignin biosynthesis genes were altered in response to applied GA(3). Our data indicate that GA may play important roles in xylem growth and lignification in carrot roots. Further studies shall focus on regulating plant lignification, which may be achieved by modifying GA levels within plant tissues.