Membrane phospholipid catabolism and Ca2+ activity in control of senescence |
| |
Authors: | Ya'acov Y. Leshem |
| |
Affiliation: | Dept of Life Sciences, Bar-Han Univ., Ramat-Gan 52 100, Israel. |
| |
Abstract: | Leshem, Y. Y. 1987. Membrane phospholipid catabolism and Ca2+ activity in control of senescence. A key role in the regulation of plant development and senescence appears to be a finely balanced equilibrium between membrane phospholipid catabolism on the one hand, and synthesis and remodelling on the other. In the catabolic “phosphatidyl-linoleyl(-enyl) cascade”, entering of Ca2+ into the cytosol triggers the catabolic process by binding to calmodulin and activating phospholipase A2, (EC 3.1.1.4). The latter proceeds to release linoleic or linolenic acid from the sn-2 (stereospecific numbering) location of intact phospholipid, thus providing substrate for lipoxygenase (EC 1.13.11.12). The action of lipoxygenase then generates a series of oxy-free radicals, ethylene, endogenous Ca2+ ionophores, malondialdehyde and jasmonic acid. These may recycle to the membrane, causing the entry of more Ca2+ and induction of a further, identical catabolic cycle. With increased cycling, membranes become progressively senescent and undergo biophysical changes altering microviscosity, fluidity, phase configurations of membrane phospholipids and transition temperatures. The cascade does not appear to be specific for the phospholipid substrate, and it is envisaged that besides phospholipase A2, both phospholipase B (EC 3.1.1.5) and lipolytic acylhydrolase could participate in the process. A parallel process counteracting the above, is membrane remodelling and turnover, proceeding initially by the same Ca2+- and possibly calmodulin-triggering, but leading via phospholipase C (EC 3.1.4.10) action and diacylglycerol formation to protein kinase activation and proton pump recharging. It is speculated that auxin and cytoki-nin, albeit by different pathways, induce this route, for which membrane phospho-inositides may be the preferred membrane-associated phospholipid substrate. |
| |
Keywords: | Ca2+-ATPase calmodulin diacylglycerol phosphatidylinosi tol phosphatidyl-linoleyl(-enyl) cascade phospholipase protein kinase |
|
|