LATERAL ROOT INITIATION BY ASYMMETRICAL TRANSVERSE DIVISIONS OF PERICYCLE CELLS IN 4 PLANT-SPECIES - RAPHANUS-SATIVUS, HELIANTHUS-ANNUUS, ZEA-MAYS, AND DAUCUS-CAROTA

In roots of Raphanus sativus, Helianthus annuus, Zea mays, and Daucus carota, lateral root initiation occurs when a pair of neighbouring elo ngated and highly vacuolated pericycle cells in the same column almost simultaneously undergo asymmetrical transversal division. This produc es a pair of very short pericycle cells lying end-to-end, flanked abov e and below by two longer cells. This occurs because both mitoses occu r close to the ends of the neighbouring pericycle cells. The two longe r daughter pericycle cells divide again later. In roots of radish, sun flower, and carrot these cells divide transversely and asymmetrically, producing more short cells adjacent to the previous ones. In corn roo ts, they undergo oblique divisions. Much later, the first pair of shor t pericycle cells undergoes periclinal divisions. Although such pericl inal divisions of pericycle cells are generally thought to mark latera l root initiation, our results show that the first pair of short neigh bouring pericycle cells in the same column offers another morphologica l criterion which permits identification of the site of lateral root i nitiation, both earlier and nearer to the apex than previously documen ted.