Competitive inhibition of the auxin‐induced elongation by α‐D‐oligogalacturonides in pea stem segments

Abstract

Branca, C, De Lorenzo, G. and Cervone, F. 1988. Competitive inhibition of the auxin‐induced elongation by α‐D‐oligogalacturonides in pea stem segments. ‐ Physiol. Plant. 72: 499–504.α‐D‐galacturonide oligomers (OG) were prepared by partial hydrolysis of sodium polypectate with an homogeneous Aspergillus niger endopolygalacturonase (EC 3.2.1.15). OG, obtained after digestion for 10, 20, 30, 60, 120 min and 24 h, were assayed for their ability to interfere with the IAA‐induced elongation of pea (Pisum sativum L. cv. Alaska) stems. Maximum inhibiting activity was exhibited by oligomers with an approximate degree of polymerization higher than 8. Inhibition by longer OG was much lower, and the products of the 24 h digestion and the unhydrolysed polypectate were ineffective. The addition of OG to pea stems caused a parallel shift to the right of the IAA dose‐effect curve. The shift depended on the amount of OG used, showing that oligogalacturonides behave as competitive antagonists of IAA. The presence of OG caused the disappearance of the second maximum of the elongation rate and reduced the first maximum. OG were also tested for their ability to inhibit IAA‐induced ethylene evolution of pea stem segments. Maximal inhibition was obtained with OG of the same size as those that interfered with IAA‐induced elongation. Inhibition of the auxin action seemed to be specific as OG did not interfere with the activity of gibberellic acid (GA3) or kinetin. It was concluded that oligogalacturonides strongly interfere with the activity of IAA, although they are by themselves incapable to influence the elongation of pea stem segments directly.