| Summary: | The coconut palm (Cocos nucifera L.) is a major crop plant which does not develop axillary shoots and must therefore be propagated from seed. As it is a heterozygous outbreeder, seedlings are variable and only after a long juvenile stage (4-7 years) can their performance be assessed. Thus the establishment of a reliable micropropagation method for elite palms is required. Much research has been devoted to this, but the recalcitrant character of the coconut palm in vitro has limited progress. The induction of embryogenic callus is the first stage in such a procedure and is the subject of this thesis. Immature inflorescence has been much used as a source of explants, but the rates of embryogenic callus production have been low. Values not exceeding 0.1% with low reproducibility were obtained in this investigation and therefore alternative sources of tissue have been explored. Experiments with zygotic embryos showed that while mature embryos were unsatisfactory for the culture of embryogenic callus, immature zygotic embryos yielded callus in considerable amounts. Isolation of plumular tissue from mature zygotic embryos gave embryogenic callus in around 80% of explants. This success level exceeded other systems reported to date. Development of clonal plantlets from plumular callus further indicated the significance of this as a useful tissue for further research. The synthetic auxin 2,4-D is normally used for the initiation of callus, but other synthetic auxins with related chemical structures were also examined. The highest yields of embryogenic callus (85 %) were obtained from plumules incubated with picloram at 6 x 10"* M in media containing activated charcoal (AC). Levels up to 2 X 10^ M picloram were also tolerated. The effect of AC in reducing the availability of regulators in media has been examined, using radio-labelled fluroxypyr acid, clopyralid and 2,4-D. Traces of suspended AC in media held a significant proportion of the auxin in solution. The release of adsorbed auxins from AC in culture media was achieved by the addition of certain organic acids. The monoclonal antibody ICS which hybridised with a 50 Kda protein in early embryogenic cultures of various monocotyledonous species was found to hybridise to a 50 Kda protein in coconut. Whether the presence of this protein is related to the embryogenicity of coconut cultures remains to be determined.
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