Involvement of endogenous plant hormones (IAA, ABA, GAs) in leaves and flower bud formation of satsuma mandarin (Citrus unshiu Marc.)

Abstract Plant hormones (IAA, ABA, GA1/3, GA4/7) contents in the leaves of satsuma mandarin trees (Citrus unshiu Marc. `Okitsu') were measured to elucidate the relationship between endogenous plant hormones and flower buds formation. The ringing treatment to lateral branch in October enhanced the percentage of leafless inflorescence and number of flowering shoots in the following spring. While, more vegetative spring shoots were formed on bearing shoots which were left the fruit load in the previous autumn to winter. GA1/3 were the dominantly detected GAs in the leaves. Their content was higher in the leaves of the bearing shoots than in that of the vegetative shoot but was not affected by the ringing treatment. Ringing increased the percentage of leafless inflorescence and the contents of IAA and ABA in December. These results suggested that flower bud formation was inhibited by GA1/3 in October, and that high IAA and ABA content in December also promote the percentage of leafless inflorescence and the number of flower buds per node. The relationship between endogenous plant hormones and flower bud formation was discussed.