Abstract
IAA stimulated stem elongation within 1 h of treatment of Pisum sativum L. cv. Feltham First stem sections. This elongation was accompanied by an increase in the endogenous level of phosphocholine and a decrease in that of CDP choline. Measurements in vitro of the CDP-base pathway enzymes showed an increase in choline phosphotransferase and a decrease in cytidylyltransferase activity on homrone treatment. The decrease in phosphatidylcholine labeling from [14C]choline that is observed on IAA treatment of pea stem sections is caused by the decrease in cytidylyltransferase activity.