A possible role for abscisic Acid in regulation of photosynthetic and photorespiratory carbon metabolism in barley leaves.

The influence of abscisic acid (ABA) on carbon metabolism, rate of photorespiration, and the activity of the photorespiratory enzymes ribulose bisphosphate oxygenase and glycolate oxidase in 7-day-old barley seedlings (Hordeum vulgare L. var. Alfa) was investigated. Plants treated with ABA had enhanced incorporation of labeled carbon from (14)CO(2) into glycolic acid, glycine, and serine, while (14)C incorporation into 3-phosphoglyceric acid and sugarphosphate esters was depressed. Parallel with this effect, treated plants showed a rise in activity of RuBP oxygenase and glycolic acid oxidase. The rate of photorespiration was increased twofold by ABA treatment at IO(-6) molar while the CO(2)-compensation point increased 46% and stomatal resistance increased more than twofold over control plants.

Effects of prostaglandins e(2) and f(2alpha) on the electrofusion of pea mesophyll protoplasts.

The effects of prostaglandins E(2) and F(2alpha) on the electrofusion of pea (Pisum sativum cv Ran 1) mesophyll protoplasts were examined. Prostaglandins E(2) and F(2alpha) influenced electrofusion by lowering the threshold voltage necessary for fusion of dielectrophoretically arranged pairs of protoplasts. The direct current voltage threshold decreased with increasing Ca(2+) concentration up to 0.1 millimolar CaCl(2) and the effects of prostaglandins E(2) and F(2alpha) were more pronounced when CaCl(2) was present in the medium. Treatment with calcium channel blocker methoxy verapamil did not change the prostaglandin effects, while the addition of ethyleneglycol-bis (beta-aminoethyl either)-N,N,N',N'-tetraacetic acid, which binds free Ca(2+), increased the threshold voltage. Influence of prostaglandins E(2) and F(2alpha) and Ca(2+) on the membrane fluidity was investigated by analysis of pyrene fluorescence spectra. The values of the ratio between the maximum fluorescence emission intensities of the excimer and the monomer forms (I(ex)/I(mon)) indicated that prostaglandins and Ca(2+) decrease the membrane fluidity. It is proposed that electrically evoked displacement of plasmalemma components takes part in the fusion process (U Zimmermann 1982 Biochim Biophys Acta 694: 227-277). We suggest that prostaglandins E(2) and F(2alpha) facilitate the electrofusion of pea mesophyll protoplasts by changing the fluidity of plasmalemma.