CHANGES IN CARBOHYDRATE-LEVELS, ALPHA-AMY LASE ACTIVITY, INDOLEACETIC-ACID AND GIBBERELLIN-LIKE SUBSTANCES IN THE SUMMER SHOOTS OF WASE SATSUMA MANDARINE TREES GROWN INDOORS DURING FLOWER-BUD DIFFERENTIATION

The mechanism of flower-bud differentiation in satsuma mandarin (Citru s unshiu Marc. var. praecox Tanaka) as related to changes in carbohydr ate contents, a-amylase activity and levels of IAA and GA-like substan ces in the summer shoots of 6-year-old 'Ueno Wase' trees grown indoors was investigated in autumn. 1. To determine when flower-bud different iation occurred, excised summer shoots were defoliated, treated with 1 50 ppm BA, and then kept at 28 degrees C for 10 days with their bases in water. Shoots were treated from mid-October to early-December at a biweekly interval. Unitil mid-October, only vegetative shoots sprouted , whereas in early-November a considerable number of flowers emerged. Therefore, flower-bud initiation occurred to be in late-October. 2. In crease in starch content in the summer shoots coincided with the flowe r-bud initiation period. In contrast, sugar content decreased from mid -October to mid-November. Towards early December, starch content decre ased in the leaf laminas and stems, while sugar accumulation accelerat ed in the laminas, petioles, buds, and stems. From these re suits, we proposed that flower-bud differentiation of satsuma mandarin has no di rect correlation with the changes in carbohydrate contents in these pa rts of the shoots. 3. In summer shoots, a-amylase activity decreased i n early-November and increased with the advance of flower-bud developm ent. The activity in laminas was lower than that in petioles, buds, an d stems but it fluctuated greatly throughout the investigation period. 4. During the flower-bud initiation period in late-October, endogenou s GA-like substances in the buds of the summer shoots was higher than those in the petioles. IAA level in the buds was higher in mid-October than in mid-November.