[3H] GA-binding, GA receptor, characteristics and purification; GA biosynthesis and metabolism; steroid receptors; nuclei, isolation, in vitro transcription; GA-insensitive mutants; mode of GA action
Use of tritiated gibberellins ([3H] GA1, [3H] GA4) of high specific activity and purity has allowed the determination of GA-specific binding sites in several plant tissues both in vivo and in vitro. In cucumber hypocotyls and pea epicotyls which have been most investigated the binding of [3H] GA; occurs to soluble proteins. This binding is saturable ('n' =about 30 pmol. Mg-1 soluble protein), of high affinity (KD= about 70 nM), and is competed for by other GA, and derivatives in proportion to their biological activity in these tissues in vivo. Size exclusion and ion-exchange chromatography has yielded several fractions which show specific and exchangeable binding of [3H] GA4, but further purification of these fractions and discrimination whether binding is to a GA metabolizing enzyme or the GA receptor has not yet been possible. Isolated nuclei from cucumber hypocotyls also show specific and exchangeable binding of [3H] GA4. They show run on transcription in vitro. Addition of 100 nM GA4 to the transcription cocktail augments the total RNA produced and, as determined by sensitivity to α-amanitin, dramatically shifts the transcription in favor of RNA polymerase II activity. It also appears that the nuclei contain a soluble inhibitor of GA-induced transcription. GA-insensitive mutants, such as wheat varieties carrying the Rht3 gene, provide a unique tool to study the mechanism of GA action. Preliminary data indicate, however that the D6899 wheat carrying the Rht3 gene, is not a receptor mutant, rather it is a mutant which produces an inhibitor that prevents the GA-induced transcription of α -amylase genes in aleurone tissue. These and other data are reviewed with a backdrop of information about steroid receptors, and gibberellin biosynthesis and metabolism. A model of gibberellin action is presented which is consistent with published data, and some future lines of research are indicated.
Journal of the Iowa Academy of Science
© Copyright 1991 by the Iowa Academy of Science, Inc.
Srivastava, Lalit M. and Sechley, Konrad A.
"In Search Of A Gibberellin Receptor,"
Journal of the Iowa Academy of Science: JIAS: Vol. 98:
, Article 5.
Available at: http://scholarworks.uni.edu/jias/vol98/iss2/5