Gibberellin is not Associated with the Enhancing Effect of 2,4-Pyridinedicarboxylic Acid on Flower Opening of ‘Light Pink Barbara’ Carnation

Abstract

2,4-Pyridinedicarboxylic acid (2,4-PDCA) extends the vase life of cut flowers of spray-type carnations by accelerating flower opening as well as retarding senescence. Since 2,4-PDCA can inhibit 2-oxoglutarate-dependent dioxygenases, which include enzymes for gibberellin (GA) biosynthesis and catabolism, we hypothesized that GA might be involved in the enhancing effect of 2,4-PDCA on the flower opening of carnation. In this study, we tested this possibility by examining the changes in gene expression of DELLA protein (GAI), a negative regulator of GA signaling, and GA levels in carnation (Dianthus caryophyllus L. ‘Light Pink Barbara (LPB)’) flowers treated with 2,4-PDCA. We also analyzed the expression of cell expansion-related genes, xyloglucan endotransglucosylase/hydrolase (XTH), and expansin genes as markers of flower opening in the treated flowers. The transcript level of GAI gene was increased, whereas that of expansin was decreased, in petals of the 2,4-PDCA-treated flowers compared to those of the control, which was contrary to the enhancement of flower opening. Our results suggest that the changes in the expression of these genes are not associated with the enhancing effects of 2,4-PDCA. In addition, GA₃ content tended to be decreased by 2,4-PDCA treatment in the petals of opening flowers. Flower opening was not accelerated, but rather delayed, by treatment of flower buds with exogenous GA₃ and not affected by paclobutrazol, an inhibitor of GA biosynthesis, in ‘LPB’ carnation. These results suggest that endogenous GA is not associated with the enhancement of flower opening by 2,4-PDCA in carnation.