| Popis: |
In many types of animal cells the so-called phosphoinositide (PI) response is involved in the signal transduction of light, hormones or neurotransmitters [1], 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) [2]. 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) [1]. 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 [3]. The PI response is discussed now also for plants, since phosphatidylinositol (4) monophosphate (PIP) and PIP2 as lipids [4], their specific lipid kinases [5] as well as the phosphoinositidase C [6] 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. |
