Poster: Growth Regulators and Hormones

Abs # 714: Regulation gibberellin metabolism by environmental factors in Arabidopsis thaliana.

Presenter:	Doong, Tzyy-Jye , doong.2@osu.edu
Authors	Doong, Tzyy-Jye  (A)   Metzger, James D. (A)
Affiliations:	(A): Department of Horticulture and Crop Science, The Ohio State University

Environmental factors such as light and temperature play an important role in plant development. It has been well known that the bolting response associated with flowering in Arabidopsis and other rosette species is regulated by gibberellin(GA). Presumably there are one or more blocks in the GA biosynthetic pathway that are removed following induction of flowering by either long-days(LD) or vernalization. We have attempted to identify steps in biosynthesis regulated by photoperiod and vernalization in Arabidopsis thaliana by comparing the biological activities of native GAs and GA precursors under inductive and non-inductive condition. We used a T-DNA tagged dominant mutant with a cold requirement line( flf ) and a recombinant inbred line selected for a LD requirement(CS933) to conduct this research. For 20 carbon GAs common feature that distinguished between active and inactive compounds was the oxidation state of C-20. GA precursors and GAs containing a C-20 methyl group (i.e. GA₁₂, GA₅₃, and GA₁₄) were not active, while GAs containing a C-20 aldehyde (GA₁₉, GA₂₄, and GA₃₆) had substantial biological activity when applied to non-induced plants of both response types. In addition, for both 19 and 20 carbon GAs,C13 hydroxylation resulted in reduced biological activity when compare to the non-C13 hydroxylated homologs. These results suggest that 1) under non-inductive condition C-20 oxidation is the rate-limiting step in the synthesis of bioactive GAs ; 2) both vernalization and LD regulate GA biosynthesis at the same control point; 3) the non C13 hydroxylation pathway leading to GA₄ may be more important in regulating stem growth than the early C13 hydroxylation pathway leading to GA₁.