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DEVELOPMENT AND HORMONE ACTION

Developmental and Embryo Axis Regulation of Gibberellin Biosynthesis during Germination and Young Seedling Growth of Pea¹

Plant Physiology and Molecular Biology Research Group, Department of Agricultural, Food, and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada T6G 2P5 (B.T.A., J.A.O., D.M.R.); and Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada T2N 1N4 (L.V.K.)

The expression patterns of five genes (PsGA20ox1, PsGA20ox2, PsGA3ox1, PsGA2ox1, and PsGA2ox2) encoding five regulatory gibberellin (GA) biosynthesis enzymes (two GA 20-oxidases, a GA 3-hydroxylase, and two GA 2-hydroxylases) were examined to gain insight into how these genes coordinate GA biosynthesis during germination and early postgermination stages of the large-seeded dicotyledonous plant pea (Pisum sativum). At the time the developing embryo fills the seed coat, high mRNA levels of PsGA20ox2 (primarily responsible for conversion of C20-GAs to GA₂₀), PsGA2ox1 (primarily responsible for conversion of GA₂₀ to GA₂₉), and PsGA2ox2 (primarily responsible for conversion of GA₁ to GA₈) were detected in the seeds, along with high GA₂₀ and GA₂₉ levels, the enzymatic products of these genes. Embryo maturation was accompanied by a large reduction in PsGA20ox2 and PsGA2ox1 mRNA and lower GA₂₀ and GA₂₉ levels. However, PsGA2ox2 transcripts remained high. Following seed imbibition, GA₂₀ levels in the cotyledons decreased, while PsGA3ox1 mRNA and GA₁ levels increased, implying that GA₂₀ was being used for de novo synthesis of GA₁. The presence of the embryo axis was required for stimulation of cotyledonary GA₁ synthesis at the mRNA and enzyme activity levels. As the embryo axis doubled in size, PsGA20ox1 and PsGA3ox1 transcripts increased, both GA₁ and GA₈ were detectable, PsGA2ox2 transcripts decreased, and PsGA2ox1 transcripts remained low. Cotyledonary-, root-, and shoot-specific expression of these GA biosynthesis genes and the resultant endogenous GA profiles support a key role for de novo GA biosynthesis in each organ during germination and early seedling growth of pea.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Jocelyn A. Ozga (jocelyn.ozga{at}ualberta.ca).

www.plantphysiol.org/cgi/doi/10.1104/pp.106.086199

^* Corresponding author; e-mail jocelyn.ozga{at}ualberta.ca; fax 780–492–4265.

Received July 2, 2006; accepted September 20, 2006; published September 29, 2006.

This article has been cited by other articles:

				J. A. Ozga, D. M. Reinecke, B. T. Ayele, P. Ngo, C. Nadeau, and A. D. Wickramarathna Developmental and Hormonal Regulation of Gibberellin Biosynthesis and Catabolism in Pea Fruit Plant Physiology, May 1, 2009; 150(1): 448 - 462. [Abstract] [Full Text] [PDF]