Endogenous protein phosphorylation and casein kinase activity during seed development in Araucaria angustifolia

Protein kinases and phosphatases are responsible for several cellular events mediated by protein phosphorylation and dephosphorylation. Among these events are cell growth and differentiation and cellular metabolism. Casein kinase I (CKI) and casein kinase II (CKII) are involved in the phosphorylation of several substrates. Endogenous protein phosphorylation and casein kinase activity were investigated in the megagametophyte of the native Brazilian conifer Araucaria angustifolia, during seed development. It was observed that a number of different polypeptides are phosphorylated in vitro in the three megagametophyte stages of development tested (from globular, cotyledonary and mature embryos, respectively) and the phosphate was incorporated mainly in serine residues. The use of okadaic acid and vanadate in the phosphorylation reactions increased phosphate incorporation in several polypeptides suggesting the presence of serine/threonine as well as tyrosine phosphatases in the megagametophyte. Also, the results obtained in experiments with CKII inhibitor, GTP as phosphate donor, RNA hybridizations, and in-gel kinase assays indicate the presence of CKII in the A. angustifolia megagametophyte.