Somatic Embryogenesis in Cocos nucifera L.

Abstract

In our coconut laboratory micropropagation has been the subject of research for nearly three decades, as this plant species is highly recalcitrant for in vitro regeneration and so far only achieved through somatic embryogenesis as the sole path for coconut regeneration. Of all the explants tested, plumules have proved to be the most responsive and the process efficiency has been improved by indirect embryogenesis and thereafter secondary embryogenesis and callus multiplication, this strategy is currently applied in floral explants. Two different approaches have been used to find ways to have a more efficient protocol. The first one, a direct and practical method, included plant hormones and activated charcoal. On the other hand, the indirect approach consisted in basic studies on: morphohistological development, biochemical and physiological aspects such as uptake of exogenous auxin, levels of endogenous auxin; shoot apical meristem formation and maintenance (KNOX gene family); the occurrence and expression of genes related to the cell cycle control (Cyclin-Dependent Kinase), and somatic embryogenesis (Somatic Embryogenesis-Related Kinase); and the establishment of a transformation protocol. A better understanding of the somatic embryogenesis of coconut was achieved by these approaches. This way, in the short term there is no doubt that we will have mass propagation options based not only in plumule explants but also on rachillae, unfertilized ovary, and leaf explants.