Distribution of Indolyl-3-acetic Acid labelled with Carbon-14 in Avena

Abstract

THE active transport of hormones in plants has been under investigation for a number of years. Speeds of transport have been reported in the literature, but there does not appear to have been any attempt to observe experimentally whether a well-defined front exists for the moving hormone stream. This lack of experiment is surprising since, as Canny¹ has pointed out, a speed of transport of a substance in a plant can only be simply defined if there exists a definite front to the stream of that substance. Such a front does not exist for translocated photosynthate nor would it be expected for hormone transport if the movement of the hormone were a diffusion-like process. Goldsmith and Thimann² find an exponential profile of a hormone in a section of Avena through which it had been passing for several hours. They assumed from this that no definite front exists and therefore they did not attempt an accurate measurement of transport speed.