Changes in phosphatidylinositol and phosphatidylinositol monophosphate kinase activities during the induction of somatic embryogenesis in Coffea arabica

Abstract

Evidence was obtained for the presence of phosphatidylinositol (PIK) and phosphatidylinositol monophosphate kinase (PIPK) at different developmental stages during somatic embryogenesis in Coffea arabica L. by in vitro phosphorylation of endogenous lipids in the presence of [γ‐32P]ATP followed by thin‐layer chromatography. The results indicate the existence of a relationship between the development stages that were analysed and the kinases found. In cells without differentiated structures (EC, embryogenic calli) phosphatidylinositol kinase and phosphatidylinositol monophosphate 5‐kinase (EC 2.7.1.68) activities were present. These activities increased significantly in the first differentiated stage (PREG, preglobular structures) and decreased as the development stages advanced. Phosphatidylinositol monophosphate (PIP) formation decreased from the globular (GLO) to the cotyledonary (COT) stage. The PIP fraction contained both isomers, PI 3‐P and PI 4‐P. This demonstrates PI3K (EC 2.7.1.137) and PI4K (EC 2.7.1.67) activity during somatic embryogenesis in Coffea arabica L. When wortmannin, an inhibitor of PI3K and PI4K activities, was included in an in vitro assay, a dose‐dependent inhibition of the formation of both isomers was observed. The addition of wortmannin to the induction medium during the PREG stage reduced the number of normal embryos. Our results suggest that PI and PIP kinases and the formation of certain phosphoinositides may play roles in the regulation of somatic embryo development in Coffea arabica L.