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Characterization of gibberellin overexpression lines in pea Open Access


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Type of item
Degree grantor
University of Alberta
Author or creator
Wickramarathna, Aruna
Supervisor and department
Dr. Jocelyn Ozga (Department of Agricultural, Food and Nutritional Science
Examining committee member and department
Dr. Allen Good (Department of Biological Sciences)
Dr. Neil Emery (Department of Biology, Trent University)
Dr. Randall Weselake (Department of Agricultural, Food and Nutritional Science)
Dr. Walter Dixon ((Department of Agricultural, Food and Nutritional Science)
Department of Agricultural, Food and Nutritional Science

Date accepted
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Doctor of Philosophy
Degree level
Abstract Gibberellins (GAs) are a class of plant hormones that regulate many aspects of plant growth and development including seed germination, stem elongation and fruit development. To investigate the regulation of GA biosynthesis and the impact of altered GA levels on plant growth and development, transgenic pea (Pisum sativum L. cv. Carneval) plants were generated to overexpress PsGA3ox1 (codes for GA 3β-hydroxylase which converts GA20 to bioactive GA1) under the control of the CaMV-35S promoter. Increased expression of the transgene PsGA3ox1 was correlated with altered plant phenotype including longer internodes, larger stipules and tendrils, and longer pods. Transgenic lines also showed upregulation of the GA catabolic genes PsGA2ox1 and/or PsGA2ox2, suggesting that GA1 substrate-induced feedback regulation also occurs to maintain GA homeostasis. Changes in endogenous GAs, quantified using an isotope dilution method, indicated that an increased flux in GA biosynthesis occurred in the expanding internodes, stipules and tendrils of the PsGA3ox1-overexpressor lines. Higher bioactive GA1 levels and growth were correlated with lower PsGA2ox1 transcript levels in elongating internodes, and oscillation of these parameters between adjacent elongating internodes in the PsGA3ox1-overexpression lines suggests that coordination of bioactive GA levels and growth occurs between adjacent internodes. During germination and early seedling growth, GA gene expression studies suggested that PsGA3ox1-overexpression increased the flux through to bioactive GA in the cotyledons, shoots and roots of pea seedlings, resulting in longer shoots but shorter roots. Auxins are a class of plant hormones involved in growth and differentiation of plants that can influence GA biosynthesis and action. The location and action of auxins is in part regulated by auxin carrier proteins. The expression patterns of the putative auxin efflux carrier genes PsPIN1 and PsPIN2 in elongating internodes were correlated with vascular re-patterning events in this tissue, and PsGA3ox1-overexpression appears to increase internode PsPIN1 and PsPIN2 transcript abundance and the formation of the vascular connections between the internode and the axillary buds. Overall, characterization of PsGA3ox1-overexpressor lines in pea demonstrated that bioactive GA levels are tightly regulated in pea tissues for the coordination of plant growth and development.
License granted by Aruna Wickramarathna ( on 2009-09-28T22:56:36Z (GMT): Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of the above terms. The author reserves all other publication and other rights in association with the copyright in the thesis, and except as herein provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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