Relationship between Promotion of Xyloglucan Metabolism and Induction of Elongation by Indoleacetic Acid

Auxin promotes the liberation of a xlyoglucan polymer from the cell walls of elongating pea (Pisum sativum) stem segments. The released polymer can be isolated from the polysaccharide fraction of the water-soluble portion of tissue homogenates, thus providing as assay for this kind of metabolism. Promotion of xyloglucan metabolism by auxin begins within 15 minutes of hormone presentation. The effect increases with auxin concentration in a manner similar to the hormone effect on elongation. However, the xyloglucan effect of auxin occurs perfectly normally when elongation is completely blocked by mannitol. Metabolic inhibitors and Ca(2+), on the other hand, inhibit auxin promotion of elongation and of xyloglucan metabolism in parallel. The results suggest that the changes in xyloglucan reflect the means by which auxin modifies the cell wall to cause elongation.