A MORPHOMETRICAL ANALYSIS OF ULTRASTRUCTURAL-CHANGES DURING THE CELL-CYCLE OF PROROCENTRUM-TRIESTINUM USING STEREOLOGY

The ultrastructural changes of the dinoflagellate Prorocentrum triestinum Schiller were quantitatively analyzed during its cell cycle using stereological procedures on ultrathin serial sections and transmission electron microscopy. The absolute volume growth and volume variations of different structural parameters were calculated during a cell cycle. Cell organization was characterized using relative parameters: volume change of nuclei, chloroplasts, mitochondria, storage products and other organelles. Storage products were the cellular compartment with the highest degree of variation during the cell cycle. The changes in the total numbers of mitochondria and chloroplasts were also estimated. There was a high variation in the total number of mitochondria during the cell cycle, while the chloroplasts showed a synchronic division just before cytokinesis. The velocity of change of the ultrastructural organization was also evaluated. In the cell cycle of P. triestinum three periods could be established: the first 8 hours of the light-phase with a fast change period; the next 6 hours with a slow change period; and the last 10 hours, including the dark-phase period, with the highest velocity of change.