BIOCHEMICAL AND PHYSIOLOGICAL ASPECTS OF LEAF DEVELOPMENT IN COCOA (THEOBROMA CACAO L.)

VIII. EXPORT AND DISTRIBUTION OF 14C AUXIN AND KININ FROM THE YOUNG AND MATURE LEAVES

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Summary

The export and translocation of radioactivity supplied as 14C-auxin or as a 14C-kinin to a donor leaf of cocoa was followed at different stages of the flush cycle to see whether there was any correlation between the pattern of movement of these growth promoters and apical bud activity. The auxin 3-indole (1-14C) acetic acid, (14C-IAA), and the cytokinin, 6-benzyI-amino (8-14C) purine, (14C-BAP), were introduced into the plant by foliar feeding. Export of the radioactivity derived from the 14C-IAA was predominantly basipetal at all stages of the flush cycle. Most of the tracer accumulated in the lower stem but there was a significantly high proportion in the older leaves. It appeared that the largest proportion of the radioactivity derived from 14C-IAA was found in parts of the plant where growth, or possibly carbohydrate accumulation, was active. It is suggested that the movement of 14C-IAA and its metabolites in cocoa may be largely determined by the direction of flow of the assimilate stream. The identity of the radioactive compounds exported from the donor leaf showed that some 80 % of the fed 14C-IAA was metabolized to other indole compounds including indole aldehyde, indole aspartate and indole acetonitrile.

When the 14C present in particular plant parts was expressed as a relative radioactivity ratio, this value, for the apical bud, declined throughout the flush cycle, being highest at bud break, indicating that the capacity of the bud to accumulate radioactivity derived from 14C-IAA was greatest during the stages of leaf production.

The distribution of radioactivity from 14C-BAP indicated both acropetal and basipetal transport of cytokinin but accumulation of radioactivity occurred only in actively growing regions. Unlike 14C-IAA, the 14C-BAP exported from the leaf was not extensively metabolized and about 60% of the transported radioactivity was detected as 14C-BAP and the remainder as conjugated 14C-BAP. For this compound the relative radioactivity ratio in the bud was highest at dormancy break (F-1), suggesting that cytokinin movement to the bud was related to the breaking of dormancy. The changes in pattern of transport of auxin and cytokinin throughout the cocoa plant were correlated with the stages of the flush cycle.

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