In order to study a possible involvement of cdc-like protein kinases in cell development and tissue differentiation, a polyclonal antibody raised against the evolutionary conserved PSTAIR-region of p34cdc2-homologue protein kinases (PSTAIR-proteins) was applied to sections of the maize root apices. PSTAIR-proteins were localized in the nuclei and the cytoplasm of cells in the root meristem, including the quiescent centre (QC), and of all dividing cells that form the lateral root primordia. In most root tissues, the amount of cytoplasmic PSTAIR-proteins progressively declined with increasing distance from the root cap junction, becoming restricted to the nucleus after the cessation of cell divisions. This occurred much nearer to the root cap junction in cells of the stele, especially in metaxylem cells, than in cells of the root cortex. Interesting exceptions were cells of the pericycle, endodermis and the outermost cell rows of stelar parenchyma, which exhibited relatively high levels of the cytoplasmic PSTAIR-proteins throughout all developmental zones. After root wounding, rapid cytoplasmic accumulation of PSTAIR-proteins in cells adjacent to the wound was observed in all tissues of the meristem and of the elongation zone. This wound response, which was usually followed by newly-induced cell divisions, was delayed with increasing distance from the root cap junction in a tissue-specific manner. Since PSTAIR-proteins were found in the cell nuclei throughout all developmental zones, they seem to have some nuclear functions which continue even after cell division has stopped.