Gibberellin perception at the plasma membrane of Avena fatua aleurone protoplasts

Abstract

A functional assay for gibberellin (GA) receptors is described based on the induction of α-amylase gene expression in isolated aleurone protoplasts of Avena fatua L. by GA4 immobilised to Sepharose beads. A 17-thiol derivative of GA4, shown to be biologically active with aleurone protoplasts, has been coupled to epoxy-activated Sepharose 6B. This GA4-17-Sepharose induces high levels of α-amylase when incubated with isolated aleurone protoplasts, while cells of the intact aleurone layer do not respond appreciably to the immobilised GA4. In order to eliminate the possibility that GA4 may be released from the Sepharose when incubated with protoplasts, aleurone layers and isolated aleurone protoplasts have been co-incubated, and their responses to GA4, GA4-17-Sepharose and control Sepharose estimated by determining the relative amounts of α-amylase mRNA induced in each tissue. Evidence from these experiments is consistent with the view that GA417-Sepharose induces α-amylase gene expression in aleurone protoplasts by interacting with the protoplast surface. This indicates that GA receptors may be located at, or near, the external face of the aleurone plasma membrane.

Signal Transduction in Barley Aleurone Protoplasts Is Calcium Dependent and Independent.

“…The Ca2+-dependent and Ca2+-independent signal transduction pathways from ABA may well originate from independent receptor systems. It was previously observed that only ABA presented to the extracellular face of the aleurone protoplast is effective at inhibiting a-amylase secretion (Hooley et al, 1991;Gilroy and Jones, 1994). However, preliminary experiments using microinjection of ABA suggest that intracellular ABA is active in triggering the induction of Em-GUS, suggesting an intracellular receptor (S. Gilroy, unpublished data).…”

“…Similarly, ultrastructural changes in the secretory apparatus that accompany GA stimulation have been determined (Hillmer et al, 1990). However, although the site of perception of GA and ABA is now tentatively assigned to the aleurone cell plasma membrane (Hooley et al, 1991;Gilroy and Jones, 1994), the GA and ABA perception systems and the subsequent signal transduction events remain poorly characterized.…”

Genetic Characterization and Functional Analysis of the GID1 Gibberellin Receptors inArabidopsis

“…The existence of other GA receptors and signaling pathways, perhaps specific to particular developmental processes, cannot be discounted. Indeed, there is considerable, albeit indirect, evidence for the existence of membrane-associated receptors for GA, most notably in the cereal aleurone (Hooley et al, 1991;Gilroy and Jones, 1994;Lovegrove and Hooley, 2000).…”

Rice GIBBERELLIN INSENSITIVE DWARF1 Is a Gibberellin Receptor That Illuminates and Raises Questions about GA Signaling

“…These enzymes act on storage macromolecules producing nutrients for the embryo. GA covalently bound to sepharose beads induces the expression of a-amylase genes in oat aleurone protoplasts but not in cells with an intact wall (Hooley et al, 1991). These results, along with additional control experiments, suggest that the response is not due to the release of GA from the sepharose.…”