Protein Phosphorylation in Partially Synchronized Cell Suspension Culture of Alfalfa

Abstract

Protein phosphorylation plays an essential part in the regulation of cell cycle of eukaryotes (Norbury and Nurse, 1989; Nurse, 1990). Several components of this regulatory mechanism are well characterized in fission and budding yeasts (Moreno et al., 1989; Wittenberg and Reed, 1988), Xenopus oocytes (Cyert and Kirschner, 1988) and mammalian cells (Moria et al., 1989; Draetta and Beach, 1988). Concerning our knowledge about the cell cycle regulation of higher plants, the presence of a p34^cdc2 homolog protein kinase has been shown (John et al., 1989; Feiler and Jacobs, 1990; Hirt et al., 1990). In order to obtain more information about the control mechanism of cell cycle in plants we studied the changes of in vitro phosphorylation pattern in both suspension cultured alfalfa cells partially synchronized by phosphate starvation and in alfalfa leaf protoplast culture.