Interaction of purified DNA with plant protoplasts of different cell cycle stage: The concept of a competent phase for plant cell transformation.

The polycation mediated attachment of purified tritiated DNA to plant protoplasts has been measured by quantitative microautoradiography. The automated grain counting technique used, also provides information on the cell cycle stage of individual protoplasts, which circumvents the need to synchronize the plant cell population before preparation of protoplasts. With protoplasts from asynchronously dividing suspension cultures of Nicotiana syhestris (NS-1), S-phase protoplasts appear to be inefficient binders of (3)H-DNA, as compared with G1 or G2 protoplasts. Protoplasts derived from a tumour line of Crepis capillaris (CAPT) exhibit (3)H-DNA binding at all cell cycle phases, but Sphase protoplasts appear to be preferential binders. These differences are discussed with reference to cell cycle kinetics, membrane charge variation and the possibility of increasing the efficiency of genetic transformation of higher plant cells in culture.