Des variations d'activités de la 5′-nucléotidase et de l’adénylate-cyclase sont-elles des composantes de la levée d'inhibition du bourgeon cotylédonaire du pois?

Abstract

Adenylate cyclase and 5′-nucleotidase activities were localized at the ultrastructural level. Variations of these activities were checked in the transfer cells of the cotyledonary node in the intact or decapitated plant. They were also studied in the shoot apex of both inhibited (G0 state) and released cotyledonary buds, during the transitions G1–S orG2–M. The adenylate cyclase activity is mainly associated with the exterior side of the plasma membrane and it is identical in both specialized and meristematic cells, no matter what the phase of the cell cycle is. Sodium fluoride did not appear as an activator of the plant enzyme adenylate cyclase. The 5′-nuelcotidase activity was predominant on the outside of the plasma membrane and in the plasmodesmata with no variation of intensity in the meristematic cells of the bud in relation to the cell cycle phases. Use of inhibitors of alkaline phosphatase (L-p-bromotetramisole and L-phenylalanine) and 5′-nucleotidase activities (α-β-methylene adenosine 5′-diphosphate) demonstrated the specificity of the reaction along the plasma membrane. The constancy of adenylate cyclase and 5′-nucleotidase activities in both inhibited and released buds suggests that if the optimization of the pool of polynucleotides is a component of the release from inhibition in the cotyledonary bud of pea, it is not due to the variation of activities of enzymes which release adenosine from ATP.