INDUCTION OF STOMATAL CLOSURE BY VANADATE OR A LIGHT/DARK TRANSITION INVOLVES CA2+-CALMODULIN-DEPENDENT PROTEIN PHOSPHORYLATIONS

Previous studies indicate that a continual source of adenosine 5'-triphosphate is required for both opening and closing of stomata. However, vanadate (Na3VO4 at 500 mu M) as well as a light/dark transition induced stomatal closing in epidermal peels of Commelina communis L., showing that the stoppage or even the decrease of the activity of the plasma membrane H+-adenosine 5'-triphosphatase is sufficient to induce stomatal closure. Furthermore, stomatal closing in response to Na3VO4 or a light/dark transition was suppressed by inhibitors of metabolism (10 mu M carbonyl cyanide m-chlorophenylhydrazone) and of protein kinases (20 mu M 1-[5-iodonaphthalene-1-sulfonyl]-1H-hexa-hydro-1,4-diazepine), calmodulin antagonists (20 mu M N-[6-aminohexyl]-5-chloro-1-naphthalenesulfonamide), and the anion channel blocker 5-nitro-2,3-phenylpropyllamino benzoic acid (50 mu M) These data suggest that the slow, outward rectifying anion channel, whose opening would be related to the membrane potential, and at least one step requiring a protein phosphorylation by a Ca2+-calmodulin-dependent protein kinase of the myosin light chain kinase type might be implicated in the induction of stomatal closing by vanadate or a light/dark transition.