CONICET | Buscador de Institutos y Recursos Humanos

Several apoplastic enzymes have been involved in the control of the elongation growth of plant cells.Among them, peroxidases contribute to both loosening and stiffening of the cell wall. They appear to be regulated by different mechanisms including the action of extracellular inhibitors. To obtainevidences of the role of the interaction Enzime-Inhibitor during leaf development the intercellular washing fluids from Helianthus annuus leaves of different ages were isolated by standard methods of vacuum infiltration and centrifugation. Peroxidase activities, assessed using tetramethylbenzidine a substrate, increased along leaf development reaching its maximum value after the organs became fully expanded. An inhibitor, chemically characterized as ascorbate, colocalized with the enzyme in the apoplast. The strong negative correlation observed between ascorbate content and peroxidase activity was relevant to show that in growing young leaves the in planta ascorbate concentrations are able to restrain the enzymatic activity. Then, at the time of growth cessation, the loss of extracellular ascorbate releases the enzyme that would contribute to wall fixation.