Pericycle proliferation pattern during the lateral root initiation in adventitious roots ofAllium cepa

Summary Far from the apical meristem of adventitious roots ofAllium cepa, the pericycle shows great proliferative activity related to lateral root initiation. A group of mother pericycle cells undergoes asymmetrical transverse and periclinal divisions following a well-established pattern. Successive asymmetrical transverse divisions, progressing from one end of the cell to the other, divide the original mother cell into very short derivatives. Later, these short derivative cells undergo periclinal divisions. This proliferative activity starts nearly simultaneously in two elongated and highly vacuolated pericycle cells located in the same column in front of one of the xylem poles. Then proliferation expands centrifugally towards other pericycle cells in the same and adjacent columns. The proliferative activity of the pericycle cells decreases progressively outwards. Only the most central of these cells produce derivatives which contribute to the future lateral root.