Evidence Against the Involvement of Galactosidase or Glucosidase in Auxin- or Acid-stimulated Growth.

Research on the mode of action of auxin in the promotion of growth has shown that auxin treatment leads to hydrogen ion secretion and wall acidification. It has recently been reported that auxin stimulates cell wall beta-galactosidase activity in Avena coleoptiles, presumably by causing cell wall acidification, since the pH optimum for the enzyme is about 5.0. It has been suggested that enhancement of beta-galactosidase and/or other glycosidase activity mediates growth promotion by auxin or low pH. This hypothesis was tested by examining the effect of inhibitors of beta-galactosidase and beta-glucosidase. Severe inhibition of measureable beta-galactosidase or beta-glucosidase activity was found to have no effect on auxin- or acid-promoted growth. It is concluded that neither beta-galactosidase nor beta-glucosidase plays an important role in short term growth promotion by auxin or acid. The data do not rule out the possibility that some other cell wall glycosidase is involved in auxin or acid action.