++ 20 ref. Sum. (En)

Cocoa seedlings were grown under greenhouse conditions in the absence of any environmental stress. During a flush cycle of shoot growth, leaves of the current flush and of the previous flush were sampled at intervals and ABA levels determined by bioassay. In young expanding flush leaves (stages F-1 to F-2) amounts of both free and bound abscisic acid (ABA) were low. At full expansion (end of F-2 stage) both forms increased, particularly the bound ABA, then declined again during the dormant period (I-1 to I-2) to reach a low level at the start of the new cycle. In the leaves of the previous flush, the early stage of the cycle (F-2) was marked by a high level of free ABA which thereafter declined rapidly and remained low throughout the rest of the cycle, whereas the bound form increased at the end of F-2 and only declined at the end of the cycle. It is suggested that both the mature leaves of the current flush and the leaves of the previous flush act as sources of ABA which maintain the bud in a state of dormancy during the latter half of the growth cycle.