1985 Volume 54 Issue 3 Pages 287-292
Cytokinin and gibberllin activity in apple seeds and fruit flesh was investigated in relation to early drop of fruit. The early drop of ‘McIntosh Red’ apple fruit was enhanced by high night temperatures (25°C) given for 30 days beginning on the 10th day after full bloom. The diameters of 1200 central fruits on two trees were measured at the same point every other day to determine the onset of reduced rate of fruit enlargement, which was used to identify the potential drop fruit. Persistent fruit and potential drop fruit were collected and extracted with ethanol. An acid ether fraction and a n-butanol fraction were obtained from the ethanol extract. Activities of plant growth regulators in each fraction were bioassayed. It was found that zeatin- and zeatinriboside-like substances existed in the seed as cytokinin and that these plus an undefined cytokinin-like substances were found in the fruit flesh. Cytokinin activity in the seed was high, 40 to 70 times that in the fruit flesh. It was presumed, therefore, that the biosynthesis of cytokinin occurred in the seeds. Cytokinin activity in the seeds of potential drop fruit showed a value 1/15 to 1/40 that of persistent fruit. This may indicate that a decline in cytokinin activity is closely related to the early drop of fruit. GA3 and GA4+7 existed as gibberellins in the seeds. Gibberellin activity in seeds of the potential drop fruit was lower than that of persistent fruit. A decline in gibberellin activity may also be related to the early drop of fruit.