Perturbation of Phospholipid Membranes by Gibberellins

Abstract

SUMMARYDifferential scanning calorimetry and electron spin resonance have been used to characterize the association of gibberellic acidj and gibberellic acid, (a GA4/GA, mixture) with phospholipid membranes. The GA4/GA, mixture lowered the temperature and reduced the co-operativity of tbe main pbase transition of liposomes prepared from dipalmitoylphosphatidylcholine (DPPC), distearylphosphatidylcholine (DSPC) and dipalmitoylphosphatidylglycerol (DPPG), and eliminated the pretransition. The reduction in co-operativity of the main transition was not accompanied by a reduction in transition enthalpy, indicating that the gibberellins simply perturb the bilayer rather than complex with the phospholipid molecules. Perturbation was markedly greater at pH values approaching the pK^^ of the gibberellin carboxyl group than at pH 7. Moreover, the negatively charged DPPG was less susceptible to perturbation than the zwitterionic phosphatidylcholines. Perturbation by GAg, a physiologically inert gibberellin, was virtually imperceptible. Electron spin resonance of GA4/GA,-treated liposomes of phosphatidylcholine (PC) and phosphatidylglycerol (PG) confirmed the results obtained by differential scanning calorimetry and also indicated that the gibberellins associate with the surface of the phospholipid membranes rather than penetrate into the interior of the bilayer. The data are consistent with tbe proposal that gibberellins can influence membrane behaviour by modulating the physical properties of the lipid bilayer.

The effect of gibberellic acid on the response of leaf extension to low temperature

“…In many cases, the response results from a phase transition in membrane lipids from a liquid-crystalline to a solid gel phase (Lyons 1973;Nishida & Murata 1996), although other mechanisms may also produce a biphasic response (Martin 1986). There is evidence that GA can reduce the point of phase transition in artificial membrane systems (Pauls et al 1982). Although Stoddart, Tapster & Jones (1978) found that pre-treatment with GA had no effect on the slope, or on the inflection point, of non-specific tetrazolium reduction or amino-acid incorporation (both membraneassociated processes).…”

A Possible Role for Indoleacetic Acid, Low Temperature, and Phospholipid Metabolism in the Induction of GA3 Responsiveness in GA3 Insensitive (Rht3-Containing) Dwarf Wheat Aleurone

“…It seems clear that minor differences in fatty acid composition can influence the properties of membranes (6) and even their hormone responsiveness (2,5) and it can be expected that small differences in head group percentages will also have significant effects on membrane functions (3).…”

Die Kalziumversorgung von Äpfeln in Abhängigkeit von pflanzlichen Regelungsvorgängen

“…B . Jones 1973;Wood u. Paleg 1974;Pauls et al 1982 (Thimann 1937) eine Hemmung der Wurzelaktivität, die zu einer Senkung des Gibberellinspiegels führt. Daraus ergibt sich eine negative Rück-kopplung, die -außer bei sehr wüchsigen Bäumen -zum Stillstand des Triebwachstums und zum Eintritt in die Winterruhe führt (Saure 1971).…”