Effect of Auxin on Ascorbic Oxidase Activity in Tobacco Pith Cells. ∗

Summary

Auxin (3-indoleacetic acid)at a concentration of 3.5 mg/1 in the medium causes a striking increase in the ascorbic oxidase activity of cultured tobacco pith sections. This is subsequently accompanied by a lesser respiratory increase, by cell enlargement, and by gains in fresh and dry weight. No cell divisions occur. Since the ascorbic oxidase activity of homogenates is localized in the cell wall fraction obtained by differential centrifugation, it is suggested that the enzyme occurs in cytoplasm intimately associated with the wall. Vigorous ascorbic oxidase activity is characteristic of a variety of actively growing plant tissues examined. It is suggested that ascorbic oxidase may be causally related to cell growth.