NUCLEAR-DNA CONTENT AND ULTRASTRUCTURE OF SECRETORY-CELLS OF VICIA-FABA L STIGMA

The object of study was the level of nuclear DNA and the ultrastructur al transformations in the secretory cells of the stigma in Vicia faba L. It has been found that the stigmal cells which are active in biogen esis and exudate secretion are diploid cells whose differentiation sta rts from 2C DNA level. The presence of a population of nuclei with an amount DNA of about 2.5 C suggests that the metabolic activity of thos e cells may be regulated through supplementary incomplete replication. The ultra-structural transformations of secretory cells point to thre e stages of biogenesis and secretion of exudate. Stage I, before the s tart of the cell's secretory functions, is characterized by the develo pment of the protein synthesizing apparatus and the activity of dictyo somes. In development stage II vesicular electron-transparent exudate is secreted. Stage III of exudate biogenesis is production of lipids. They form mainly in the plastids and are secreted with the involvement of the cell's vacuolar system.