Probing a Membrane Matrix Regulating Hormone Action: II. The Kinetics of Lipid-Induced Growth and Ethylene Production.
Lipids which are active oleanimins, i.e., those which stimulate respiration and auxin-induced cell elongation of pea stem sections, also initiate a period of ethylene formation in them after a lag period of at least 1 hour. Production of ethylene requires auxin, is inhibited by cycloheximide and dinitrophenol applied during or before the lag period, and is greatly stimulated by lipids longer than 20 Angstroms in length such as heptadecyl-benzene, chloro- or iodohexadecane, triolein, and vitamins E and K(1), but not by the shorter chloro- and iododecane. beta-Stigmasterol at 10 to 40 mum concentrations depresses both oleanimin-induced growth and ethylene formation.The effect of oleanimins on the growth rate steadily declines and disappears after 6 hours, whereas oleanimin induction of ethylene stays at a high level until it rapidly disappears after 6 hours. Nongrowing second internode sections also produce ethylene on oleanimin treatment, so ethylene formation is not dependent on cell elongation even though it requires auxin. Preincubation with heptadecylbenzene or auxin does not change the delay of an hour or more before ethylene is produced, whereas increases in growth are noted at the earliest measurements. Oleanimins stimulate growth at less than optimal auxin concentration, even as low as 20 nm, where a proportional ethylene formation is not noted. It is concluded that ethylene formation is not causally related to growth in these tissues.The decline in oleanimin-induced ethylene formation is not changed by renewal of the incubation medium, and sucrose which is required to maintain growth for 20 hours does not influence growth or ethylene formation up to 6 hours. l-Methionine increases ethylene formed after heptadecylbenzene treatment, but unexpectedly, malonate is much more effective.Auxin concentrations supraoptimal for growth cause no growth rate reductions for the first 10 hours, but they greatly enhance oleanimin-induced ethylene formation even when heptadecylbenzene is added after 6 hours. Applied ethylene even at concentrations much above those produced by the tissue itself fails to stimulate or inhibit short term pea stem section growth. It is concluded that the effect of oleanmins on growth is not mediated by ethylene. The similarities in concentration and molecular dimensions of these structurally diverse lipids which simultaneously stimulate respiration, growth, and ethylene formation, suggest a single site of action located in a regulatory membrane.
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Kline Biology Tower, Department of Biology, Yale University, New Haven, Connecticut 06520.
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