Somatic embryogenesis involves different molecular events including differential gene expression and various signal transduction pathways. One of the genes identified in early somatic embryogenesis is S OMATIC E MBRYOGENESIS R ECEPTOR-like K INASE (SERK). Cocos nucifera (L.) is one of the most recalcitrant species for in vitro regeneration, achieved so far only through somatic embryogenesis, although just a few embryos could be obtained from a single explant. In order to increase efficiency of this process we need to understand it better. Therefore, the purpose of the present work was to determine if an ortholog of the SERK gene is present in the coconut genome, isolate it and analyze its expression during somatic embryogenesis. The results showed the occurrence of a SERK ortholog referred to as CnSERK. Predicted sequence analysis showed that CnSERK encodes a SERK protein with the domains reported in the SERK proteins in other species. These domains consist of a signal peptide, a leucine zipper domain, five LRR, the Serine-Proline-Proline domain, which is a distinctive domain of the SERK proteins, a single transmembrane domain, the kinase domain with 11 subdomains and the C terminal region. Analysis of its expression showed that it could be detected in embryogenic tissues before embryo development could be observed. In contrast it was not detected or at lower levels in non-embryogenic tissues, thus suggesting that CnSERK expression is associated with induction of somatic embryogenesis and that it could be a potential marker of cells competent to form somatic embryos in coconut tissues cultured in vitro.

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Research for the development of protocols for the micropropagation of coconut plants (Cocos nucifera L.) has encountered several difficulties, such as explant browning. Although browning could be overcome by adding activated charcoal, this additive can also bind components of the culture medium required for the tissue morphogenic responses; this adsorption can be up to 99 % of the growth regulators added to the medium. In this work we developed a protocol without the use of activated charcoal which is able to produce embryogenic calli from coconut palm plumules as explants. This protocol also allowed us to study the kinetic absorption of 2,4-dichlorophenoxyacetic acid (2,4-D) by the explant, otherwise impossible in medium with activated charcoal. After evaluating different concentrations of 2,4-D in culture media without charcoal or polyvinylpolypirrolydone (PVPP) instead, we found that about 43 % of coconut explants cultured in media containing 1 µM 2,4-D withoutactivated charcoal (with or without PVPP) formed embryogenic calli after four months. Yields were reproducible and similar to those obtained with medium containing activated charcoal and responses occurred more rapidly. Morphological observations of calli obtained in activated charcoal-free media were similar to those obtained in activated charcoal-containing medium. However there were differences in the histological observations, mainly in the shape of the nuclei of the proembryos of both types of callus. Uptake of 14C-2,4-D was studied in plumule explants cultured in activated charcoal-free medium. After 120 d of culture about 25 % of the original radioactivity originally in the medium was extracted from explants and their 14C-2,4-D concentration peaked within the first 20 d, before appearance of any morphogenic response.