An Auxin-Mediated Control of a Rapid Phosphoinositide Response in Isolated Plant Cell Membranes
In many types of animal cells the so-called phosphoinositide (PI) response is involved in the signal transduction of light, hormones or neurotransmitters , Extracellular signals are percepted by their specific receptors at the outside of the plasma membrane, and these informations are transduced across the membrane by the operation of high-affinity GTP-binding proteins (G proteins) . The activated G proteins stimulate obviously the phosphoinositidase C on the cytoplasmic side of the plasma membrane, which hydrolyzes membrane-bound phosphatidyl (4,5) bisphosphate (PIP2) to membrane-bound diacylglycerol and soluble inositol (1,4,5) trisphosphate (IP3) . The compounds act as second messengers for the stimulation of the protein kinase C and the release of Ca2+ from endomembrane stores, respectively [1,3]. The protein phosphorylation and the Ca2+ mobilization are suggested to cooperate as persistent and transient signals for the control of cellular processes, respectively . The PI response is discussed now also for plants, since phosphatidylinositol (4) monophosphate (PIP) and PIP2 as lipids , their specific lipid kinases  as well as the phosphoinositidase C  were found to be localized at the plasma membrane, and high-affinity GTP binding proteins of as yet unknown function [7,8] were detected on membranes of plant cells. The phytohormone auxin was found to function as one putative signal for the initiation of the PI response in plants [8,9,10,11]. This report summarizes briefly some important aspects concerning the auxin action on microsomal membranes prepared from carrot suspension cells.
KeywordsPhosphatidic Acid Phosphatidic Acid Microsomal Membrane Inositol Trisphosphate Auxin Action
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