Effect of Auxin upon Loss of Calcium from Cell Walls

Abstract

The Ca-bridge hypothesis of auxin-action has been put to a direct test by determining the effect of auxin upon the loss of Ca45 from cell walls. The loss of Ca from Avena coleoptile and maize mesocotyl cell walls is not enhanced by auxin, irrespective of whether the Ca45 was introduced into the walls at the time of wall synthesis or only afterwards. Auxin does not cause a redistribution of Ca between pectin and protopectin. It would appear that the removal of Ca cross-linkages is not mediated by auxin and that the Ca-bridge hypothesis is incorrect.