PLANT PHYSIOLOGY , Vol 106, Issue 4 1381-1387, Copyright © 1994 by American Society of Plant Biologists
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METABOLISM AND ENZYMOLOGY |
The 58-Kilodalton Calmodulin-Binding Glutamate Decarboxylase Is a Ubiquitous Protein in Petunia Organs and Its Expression Is Developmentally Regulated
Y. Chen, G. Baum and H. Fromm
Department of Plant Genetics, Weizmann Institute of Science, 76100 Rehovot, Israel
A cDNA coding for a 58-kD calcium-dependent calmodulin (CaM)-binding
glutamate decarboxylase (GAD) previously isolated in our laboratory from
petunia (Petunia hybrida) (G. Baum, Y. Chen, T. Arazi, H. Takatsuji, H.
Fromm [1993] J Biol Chem 268: 19610-19617) was used to conduct molecular
studies of GAD expression. GAD expression was studied during petunia organ
development using the GAD cDNA as a probe to detect the GAD mRNA and by the
anti-recombinant GAD serum to monitor the levels of GAD. GAD activity was
studied in extracts of organs in the course of development. The 58-kD
CaM-binding GAD is expressed in all petunia organs tested (flowers and all
floral parts, leaves, stems, roots, and seeds). The highest expression
levels were in petals of open flowers. Developmental changes in the
abundance of GAD mRNA and the 58-kD GAD were observed in flowers and leaves
and during germination. Moreover, developmental changes in GAD activity in
plant extracts coincided in most cases with changes in the abundance of the
58-kD GAD. We conclude that the 58-kD CaM-binding GAD is a ubiquitous
protein in petunia organs and that its expression is developmentally
regulated by transcriptional and/or posttranscriptional processes. Thus,
GAD gene expression is likely to play a role in controlling the rates of
GABA synthesis during petunia seed germination and organ development.
