CHARACTERIZATION OF PROTOPLASTS FROM HYPOCOTYLS OF HELIANTHUS-ANNUUS IN RELATION TO THEIR TISSUE ORIGIN

Cells and protoplasts isolated from three different tissues of sunflow er hypocotyls and cultured either in liquid or agarose medium were com pared in terms of their volume, DNA content, division potential and em bryoid formation. Epidermal and external cortical cells differ from ot her tissue cells by their small size, their weak response to plasmolys is and their low DNA content(around 1C). They contribute only very wea kly to the dividing protoplast population. In contrast, protoplasts fr om cortical and medullar cells both have similar division potential, r eaching 50%. The nuclear DNA content of these two cell types, as well as their corresponding protoplasts, has a 2C value, taking root tip ce lls in G0 phase as standard. The culture conditions induce the same sp ecific response in protoplasts isolated from both tissues: exclusively loose colony formation in liquid medium, and mainly production of emb ryoids in agarose medium.