RELATIONSHIP BETWEEN INITIATION OF CELL ELONGATION AND CELL-DIVISION IN RADICLES OF GERMINATING-SEEDS

The initiation of axial organ growth in germinating broad bean (Vicia faba var: minor) and cotton (Gossypium hirsutum) seeds was studied in terms of cell elongation and cell division. Seed imbibition occurred in polyethylene glycol (M.W. 6000) solutions at various concentrations that retarded the radicle protrusion and maintained the tissue hydration at various levels. The triggering of cell elongation in broad bean hypocotyl or cotton radicle depended on tissue hydration up to the threshold level. The initiation of cell elongation was independent of the processes preparing for the initiation of cell division in the meristems. The appearance of mitotic activity in roots was examined relative to water content in the meristem, time of radicle emergence, and root length. The initiation of cell division did not directly depend on hydration level reached and time of radicle protrusion; however, the commencement of mitoses was determined by the presence of a threshold number of elongating cells. The possibility of a ''mitotic'' factor formed by elongating cells is discussed.