Poster: Hormone synthesis & metabolism

Abs # 473: Endogenous gibberellin and auxin levels in mature embryos and young seedlings of Pisum sativum L.

Presenter:	Ayele, Belay , belay.ayele@ualberta.ca
Authors	Ayele, Belay  (A)   Ozga, Jocelyn A (A)   Reinecke, Dennis M (A)
Affiliations:	(A): University of Alberta

The endogenous levels of gibberellins (GA₁₉, GA₂₀, GA₁, GA₈, GA₂₉, and GA₃) and auxins (IAA and 4-Cl-IAA) in mature embryos and component tissues (root, shoot and cotyledon) of 4-d-old seedlings of tall (LE, cv. Alaska) and dwarf (le, cv. Carneval) pea (Pisum sativum) were determined by gas chromatography-mass spectrometry. Relative to their level in the mature embryos, there was an increase of IAA and a decrease of 4-Cl-IAA in the cotyledons 4 days after imbibition, suggesting a difference in the roles of these two auxins in the germination process. 4-d-old roots of both cultivars contained higher levels of both IAA and 4-Cl-IAA than the corresponding shoots. IAA and 4-Cl-IAA levels of 4-d-old Alaska shoots were elevated in comparison to that in Carneval shoots. Though its metabolic precursor, GA₁₉, did not accumulate to the same extent, there was elevated level of GA₂₀ in the mature embryo of Alaska which decreased markedly by 4 days after imbibition, suggesting the role of GA₂₀ as a substrate to be 3β-hydroxylated to GA₁ on germination. Some GA₁ was detected in mature embryos of both genotypes; however, no endogenous GA₁ was detected in the three organs of cv. Carneval 4 days after imbibition, indicating the biochemical expression of the le mutation in these tissues. The three tissues of Alaska seedlings contained GA₁, and its level was highest in the root. This together with the higher level of the two auxins found in the root support the theory that biologically active GA (GA₁) and auxins are mainly localized in actively growing tissue. The inactive 2β-hydroxylated GAs (GA₂₉ and GA₈) were much higher in the mature embryo and the three tissues of 4-d-old seedlings of cv. Alaska than that of cv. Carneval. Supported in part by NSERC grant #138166.