Role of Monovalent, Divalent Cations and Phenylmercuric Acetate in the Regulation of Stomatal Aperture in Euphorbia neriifolia L.

Abstract

Normally stomatal apertures in Euphorbia neriifolia remain closed in the day time. Immersion of epidermal strips in water led to an appreciable swelling of guard cells with a slight disappearance of starch grains in them but without any effect on the aperture size. The influx of K + ions caused a tremendous change in the opening of the aperture, with consequent disappearance of starch in guard cells. The influx of K + appeared to cause hydrolysis of starch, leading to an increase of osmotic amounts of guard cells, their uptake of water and finally the opening of the stomata. The K + uptake was only light-stimulated for opening of the apertures. Ca ++ did not cause any effect on the opening of stomata, either in light or darkness. The apertures in KCl-induced open stomata nearly closed down when transfered to phenylmercuric acetate (PMA) in light, associated with simultaneous appearance of starch in guard cells, as if condensation phenomenon had taken place together with the withdrawl of K ions from the guard cells with this treatment. It was also observed that uptake of PMA in light was more than in dark. More uptake of PMA result ed in complete efflux of K + , and the guard cells with lesser uptake of PMA still contained some K + , thus lowering its closing effect.