POLARIZED DNA SYNTHESIS AND CELL DIVISION IN CELL CLUSTERS DURING SOMATIC EMBRYOGENESIS FROM SINGLE CARROT CELLS

Embryogenic cell clusters derived from single cells of carrot (Daucus carota L. cv. 'Kurodagosun') showed polarized cell division during the initial stages of embryogenesis. Morphological and biochemical polarity during early embryogenesis were examined. Using an experimental system in which single cells differentiate to form embryos at high frequency, [³ H]thymidine incorporation into cells and cell clusters was followed during the initial stage of somatic embryogenesis using autoradiography. Polarized incorporation of [³ H]thymidine was observed after cell clusters passed the four-cell-stage. This polarity was preserved under conditions inducing embryogenesis, but was cancelled under conditions inducing non-embryogenic growth. This indicates that the polarity of activity of DNA synthesis may be correlated with the expression of totipotency in embryogenesis.