DESCRIPTION OF SOMATIC-EMBRYO-FORMING SINGLE CELLS IN CARROT SUSPENSION-CULTURES EMPLOYING VIDEO CELL TRACKING

A cell-tracking system was established to determine the capability of individual single suspension cells of carrot (Daucus carota L.) to develop into somatic embryos. When immobilised in phytagel, 127 out of 30 318 single suspension cells smaller than 22 mu m in diameter developed into a somatic embryo. Single cells present at the start of the experiment were classified on the basis of their morphology into five groups: small spherical vacuolated cells; small spherical cytoplasm-rich cells; oval vacuolated cells;elongated vacuolated cells and cells that could not be classified into either one of these groups. Single cells of all morphologically distinguishable single cell types developed into somatic embryos with a frequency that varied between 19 and 100 somatic embryos per 10 000 cells. This suggests that the capability of individual single cells to form somatic embryos is not restricted to a particular cell type distinguishable on the basis of its morphology. Three major pathways were observed during development. Oval and elongated cells developed into somatic embryos via an asymmetrical cell cluster. Spherical cells developed via a symmetrical cell cluster into somatic embryos. Before formation of a somatic embryo, cells of a more variable initial morphology first developed aberrantly shaped cell clusters. This suggests that the developmental pathway leading to a somatic embryo can be predicted by the initial single-cell morphology.