Elevated sensitivity to gibberellin by vernalization in the vegetative rosette plants of Eustoma grandiflorum and Arabidopsis thaliana

Changes in the sensitivity to gibberellin (GA) after vernalization were stu died in the vegetative rosette of Eustoma grandiflorum and late flowering A rabidopsis thaliana mutant, fca-1. The sensitivity to GA after vernalizatio n was monitored using the bolting rate of plants that were grown on a mediu m containing GA, or ancymidol. The bolting rates were higher in vernalized plants than non-vernalized plants when the same GA, concentration was used. There was a positive relationship between the duration of vernalization an d the bolting rate in E. grandiflorum. In contrast, a negative relationship between the duration of treatment and bolting rate was found in the non-ve rnalized plants. In fca-1, the flowering time of vernalized plants was sign ificantly reduced compared with the non-vernalized plants under various con centrations of GA, treatment. To elucidate whether this elevated sensitivit y relates to the efficiency of GA signal transduction, we measured the tran script amounts of Expansin (Esp), which is up-regulated by CA, and GA20-oxi dase (GA-20ox) and GA3 beta -hydroxylase (GA3 beta hy), which are down-regu lated by GA. The transcript amounts were estimated using the Taq-Man PCR sy stem based on combinations of primers and probes that specifically detect t he genes, and normalized by the transcript amount of ubiquitin gene measure d as an internal standard. For each concentration of GA treatments examined , Expansin of both E. grandiflorum and A. thaliana was induced at a higher rate in the vernalized plants than in the non-vernalized plants. The expres sion of GA20ox and GA3 beta hy of E. grandiflorum decreased faster in the v ernalized plants than the non-vernalized plants. We conclude that vernaliza tion is a critical environmental cue not only for initiating GA biosynthese s in vegetative rosette, but also for elevating the GA sensitivity of the p lants via a GA signal transduction pathway. (C) 2001 Elsevier Science Irela nd Ltd. All rights reserved.