The Control of Branch Growth on Potato Tubers: III. THE BASIS OF CORRELATIVE INHIBITION

Abstract

Correlatively inhibited lateral buds on potato tubers were supplied with various nutrient solutions through the surfaces of leaf primordia. The media, which also supported the growth of isolated buds in tissue culture, stimulated the growth of the dominant (growing) sprouts but the inhibited buds were not induced to grow. These findings suggest that inhibition was not due to a shortage of nutrients. The neutral fraction of the ether extract from potato tubers bearing inhibited sprouts contained a substance or substances capable, at physiological concentra tions, of inhibiting the growth of buds both in situ and when isolated. Buds on eyepieces were not inhibited when supplied with a tissue-culture medium as well as the neutral fraction. The latter contained both growth-inhibiting and growth promoting substances. The inhibitor complex was partially purified. It was soluble in water and ether and was most unstable. When treated with fluorescein followed by bromine it gave a characteristic reddish-brown fluorescence. Attempts to establish its chemical nature were unsuccessful. The available evidence indicated that the substance(s) was effective in preventing the extension of potato buds at concentrations approxi mating to those found in situ and that it disappeared from tuber tissue within 24 h of removing the growing sprouts. It is suggested that this complex, which is rapidly metabolized in tissue, is the prime component involved in apical dominance. Nutrient supply does not appear to be directly involved although a ready supply of nutrients can partially offset the effect of the inhibitor.