1996 Volume 65 Issue 2 Pages 245-253
Seasonal changes of contents of endogenous GAs in vegetative organs and effect of harvesting date on endogenous GA synthesis were surveyed. Simultaneously, the influence of paclobutrazol, a gibberellin (GA) synthesis inhibitor, on the induciton of flowering in satsuma mandarin was evaluated.
1. GA1 content in leaf of vegetative shoot increased from 26 Jul. to 26 Sep., decreased to 28 Jan., and increased again to 24 Mar. On the contray, GA20 and GA19-like activities were the lowest on 26 Sep.; their maximum acitvities were recorded on 29 Nov. and 28 Jan., respecitively. The trends of GAs in the axillary buds were closely paralleled with those in the leaves.
2. A foliar spray with 1, 000 ppm pacloburazol on 1 Feb. increased the numbers of flowers, and decreased GA20 and GA19-like activities in leaf, but it did not affect GA1 acivity.
3. The early harvest in October increased the number of flowers the following season compared to the late harvest in December. GA20 activity in the leaves of the vegetative shoots on the ealy harvested tree was lower than those of the late harvested tree at the end of November and January.
Thus, paclobutrazol treatment reduced the level of GA1 precursor, but not GA1, which is in agreement with the metabolism of endogenous GAs in the early harvested tree. The inhibition of GA synthesis by paclobutrazol is one of the physiological evidence which indicate that GA plays a role in flowering in satsuma mandarin.