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

Correlatively inhibited lateral buds on potato tubers were suppliedwith various nutrient solution through the surfaces of leafprimorida. The media, which also supported the growth of isolatedbuds in tissue culture, stimulated the growth of the dominant(growing) sprotus but the inhibition was not due to a shortageof nutrients. The neutral fraction of the ether extract frompotato tubers bearning inhibited sprotus contained a substancesor substances capable, at physiological concentrations, of inhibitingthe growth of buds both in situ and when isolated. Buds on-eyepieceswere not inhibited when supplied with a tissue-culture mediumas well as the neutral fraction. The latter contained both growth-inhibitingand growth-promoting substances. The inhabitor complex was partiallypurified. It was soluble in water and ether and was most unstable.When treated with fluorescein followed by bromine it gave acharacteristic reddish-brown fluorescence. Attempts to establishits chemical nature were unsuccessful. The available evidenceindicated that the substance(s) was effective in preventingthe extension of potato buds at concentrations approximatingto those found in situ and that it disappeared from tuber tissuewithin 24 h of removing the growing sprouts. It is suggestedthat this complex, which is rapidly metabloized in tissue, isthe prime component involved in apical dominance. Nutrient supplydoes not appear to be directly involved although a ready supplyof nutrients can partially offset the effect of the inhibitor.