Ergosterol (a fungal membrane component) was shown to induce transient influx of protons and membrane hyperpolarization in cotyledonary cells of Mimosa pudica L. By contrast, chitosan (a fungal wall component with known elicitor properties) triggered membrane depolarization. In the processes induced by ergosterol, a specific desensitization was observed, since cells did not react to a second ergosterol application but did respond to a chitosan treatment. This comparative study correspondingly shows that ergosterol and chitosan were perceived in a distinct manner by plant cells. Generation of O2*-, visualized by infiltration with nitroblue tetrazolium, was displayed in organs treated with ergosterol and chitosan. This AOS production was preceded by an increase in activity of NADPH oxidase measured in protein extracts of treated cotyledons. In all the previously described processes, cholesterol had no effect, thereby indicating that ergosterol specifically induced these physiological changes known to participate in the reaction chain activated by characteristic elicitors. Contrary to chitosan, ergosterol did not greatly activate secondary metabolism as shown by the small change in content of free phenolics and by the low modification in activity of PAL, the key enzyme of this metabolic pathway. Therefore, future studies have to clarify the signalling cascade triggered by ergosterol recognition.
Ergosterol (a fungal membrane component) induced modification of proton fluxes and membrane hyperpolarization in motor cells of Mimosa pudica. These reactions appear specific since they were not induced by the other sterols tested. A specific desensitization was observed, since cells did not react to a second ergosterol application. Exposed at first to other sterols, cells remained reactive to ergosterol. Comparatively, chitosan (a fungal wall component with known elicitor properties) triggered a membrane depolarization and also induced specific desensitization. This comparative study shows that ergosterol and chitosan are distinctly perceived by plant cells and induced different early events at the plasma membrane level.
Primary pulvini of Mimosa pudica L. displaced from their position display gravitropic movements beginning about 15 minutes after their reorientation. Ethephon, an ethylene-releasing compound, and 1-aminocyclopropane-l-carboxylic acid, an intermediate in ethylene biosynthesis, enhance these movements at a concentration as low as 10 nanomolar.Inhibitors of ethylene synthesis (L-a42-aminoethoxyvinyl)glycine, (aminooxy)acetic acid, and Co2") reduce the amplitude of the movements. The promotive action of 1-aminocyclopropane-1-carboxylic acid is abolished by L-a42-aminoethoxyvinyl)glycine. These results permit one to conclude that ethylene may modify the curvature movement but not the initiation of the gravitropic reaction. With reference to the pulvinus functioning based on turgor variations and ion migrations inside the organ, namely K' acting as the osmoticum, the data suggest that ethylene may act by increasing the membrane permeability to water and/or by altering an ion pump.
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