Phenol content, acidic peroxidase and IAA-oxidase during somatic embryogenesis in Theobroma cacao L.

Calli were induced in cacao cotyledon explants on a half-strength Murashige and Skoog medium containing 6 x 10(-2) g m(-3) saccharose and various combinations of 2,4-dichlorophenoxyacetic acid (2,4-D) with kinetin (kin), benzylaminopurine (BAP) or 2-isopentenylphosphate (2-iP). Experiments were carried out on two clones of cacao differing in their susceptibility to black pod disease. The highest percentage of explants forming callus and the most rapid callus development were obtained with 10(-6) g m(-3) 2,4-D and 0.5 x 10(6) g m(-3) kin. Somatic embryogenesis and rhizogenesis were induced by transferring 3-week-old callus in a half strength Murashige and Skoog medium containing 3 x 10(-2) g m(-3) saccharose and NAA or IBA in the 0 to 5 x 10(-6) g m(-3) concentration range. No differentiation could be observed when the medium was supplemented with kin or BAP. The conversion of callus into somatic embryos and roots was accompanied by a drop in phenol content and an increase in peroxidase and IAA-oxidase activities. Moreover, cell differentiation was characterized by the persistence in the callus of one acidic soluble isoperoxidase which was not detected in nondifferentiating callus. Although some differences were noticed between the clones, alterations responsible for cell differentiation were the same in both genotypes.