PLANT PHYSIOLOGY , Vol 110, Issue 4 1135-1144, Copyright © 1996 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Vicilin and Napin Storage-Protein Gene Promoters Are Responsive to Abscisic Acid in Developing Transgenic Tobacco Seed but Lose Sensitivity following Premature Desiccation
L. Jiang, S. R. Abrams and A. R. Kermode
Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6 (L.J., A.R.K.)
In transgenic tobacco (Nicotiana tabacum L.) seed, expression of chimeric
[beta]-glucuronidase (GUS) genes containing the vicilin or napin
storage-protein gene promoters is responsive to premature drying and
declines upon rehydration (L. Jiang, W.L. Downing, C.L. Baszczynski, A.R.
Kermode [1995] Plant Physiol 107: 1439-1449). Desiccation may cause changes
in the content of or sensitivity to abscisic acid (ABA), partially or
wholly removing the effects of this "modulator" of developmental gene
expression. We studied the enhancement of GUS reporter enzyme activities in
transgenic tobacco by exogenous ABA before and after drying. A racemic
mixture of ABA at 10 [mu]M caused a 2- to 3-fold increase in GUS activity
in developing transgenic seed expressing chimeric genes containing the
vicilin or napin gene promoters. However, when these seeds were prematurely
dried prior to their culture on ABA medium, enhancement of GUS activity was
virtually abolished. Use of optically pure ABAs revealed that the
enhancement in GUS activity in developing fresh seed was due largely to the
natural (+) form of ABA. Chimeric constructs containing a viral 35S
promoter did not respond to ABA whether or not premature drying was
applied. Thus, vicilin and napin chimeric genes, initially sensitive to
ABA, become relatively insensitive to the hormone following drying. A
decline in ABA sensitivity may be an important factor in the cessation of
storage-protein gene expression.