Gibberellin‐photoaffinity labelling of two polypeptides in plant plasma membranes

Abstract

SummaryTwo polypeptides of M r 68 kDa and 18 kDa were gibberellin (GA)-photoaffinity labelled in vitro in plasma membrane preparations from oat (Avena sativa L.) aleurone and from leaves and stems of wild-type and GA-sensitivity mutants of different species. Labelling of these polypeptides could be competed by biologically active, but not by inactive, GAs, indicating the likely biological significance of these interactions. On 2-dimensional gels the radiolabelled polypeptides were each resolved as one intensely labelled low abundance spot with a slightly lower pI form adjacent to it. There was a strong pH dependency for both labelling events, which correlated well with pH values at which GA are known to be most biologically active. A semi-dwarf GAsensitivity mutant of sweet pea (Lathyrus odoratus L.), lb, showed reduced photoaffinity labelling of both polypeptides compared with the wild type, Lb. In the GA-insensitive Arabidopsis thaliana mutant, gai, the level of labelling was the same as in wild type, GAI. This is the first report of GA-binding proteins in plant plasma membranes. Some preliminary sequence data are given for one of the labelled polypeptides. We discuss these mutants and consider their possible roles in GA perception or action.

The Rice Alpha-Amylase, Conserved Regulator of Seed Maturation and Germination

“…Analysis of gene expression during the conversion of inactive GA to active GA, and using mutants defective in shoots and scutella formation, revealed that the scutella region of the embryo is essential for the induction of alpha-amylase [78]. Studies suggest that GA is perceived in the plasma membrane by gibberellin-binding protein (GBP) [79,80,81,82] and inside the cell by GID1 [83]. However, Kenji et al [83] showed that GBP does not exist and that the GID1-DELLA system is solely responsible for GA reception in rice aleurone cells using a gid1 mutant.…”

Gibberellin Receptor and Its Role in Gibberellin Signaling in Plants

“…Based on these observations, Hooley and his colleagues attempted to identify a GA receptor located on the plasma membrane of oat aleurone cells using a photoaffinitylabeled GA, and succeeded in detecting two GBPs: a 60-kDa protein localized in the microsomal fraction (20), and a 50-kDa protein in the cytosolic fraction (19,72). Two other GBPs of 68/18 kDa were also detected in the plasma membrane fraction from oat aleurone by the same photoaffinity-labeling method (39). Even though partial amino acid sequences for the 18-kDa GBP have been identified, there is no further information about these GBPs.…”

A gibberellin‐regulated protein phosphorylated by a putative Ca2+‐dependent protein kinase is G‐protein mediated in rice root

“…Although several GA‐binding proteins have been identified from different plants including maize (Keith & Rappaport 1987), bean (Nakajima et al . 1997), rice (Komatsu, Matsuda & Hirano 1996b), oat, pea and Arabidopsis (Lovegrove et al . 1998), their functions remain to be identified.…”