Evidence of an auxin-mediated phosphoinositide turnover and an inositol (1,4,5)trisphosphate effect on isolated membranes of Daucus carota L.
Microsomal membranes from carrot suspension cells were phosphorylated in vitro with [gamma-32P]ATP. In the presence of submicromolar concentrations of the natural auxin indoleacetic acid (IAA), a rapid, but transient decrease of the [32P] label could be detected in the phospholipid extracts of the membranes. The phytohormone effect was not the result of an inhibition of the lipid phosphorylation reactions, but was caused by a simultaneous release of water-soluble compounds, which, according to their chromatographic properties, were assumed to contain inositol polyphosphates. Although the [32P]-labeled lipids, as well as the inositol polyphosphates, were not identified unequivocally by chemical analysis, these findings point to an auxin-mediated control of a phosphoinositidase C-like reaction similar to the hormone-stimulated phosphoinositide response in animals. Exogenously applied inositol (1,4,5)trisphosphate [(1,4,5)IP3] was found to release 45Ca2+ from preloaded membrane vesicles of carrot cells. Both the detection of the auxin-stimulated phosphoinositide response and the (1,4,5)IP3-mediated Ca2+ release on isolated cell membranes offer new experimental approaches for the identification of the putative auxin receptor and its signal transduction pathway.
Zbell
B A
BA
Botanical Institute, Ruprecht-Karls-University, Heidelberg, Federal Republic of Germany.
Walter-Back
C
C
Bucher
H
H
D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D007210:Indoleacetic Acids / Q000502:physiology*; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000494:pharmacology*; D007700:Kinetics; D008055:Lipids / Q000302:isolation & purification; D008861:Microsomes / Q000187:drug effects; D010716:Phosphatidylinositols / Q000378:metabolism*; D010766:Phosphorylation; D010937:Plant Growth Regulators / Q000502:physiology*; D010944:Plants / Q000187:drug effects / Q000378:metabolism*; D013403:Sugar Phosphates / Q000494:pharmacology*
D007210:Indoleacetic Acids; D007295:Inositol Phosphates; D008055:Lipids; D010716:Phosphatidylinositols; D010937:Plant Growth Regulators; D013403:Sugar Phosphates; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium