Cell-cycle parameters of soybean (Glycine max L.) cells growing in suspension culture: Suitability of the system for genetic studies.

Suspension cultures of Glycine max (L.) Merr. were grown at 22 and 33°. The doubling times of dividing cells were 35 and 25 h, respectively. G2 was 6.2 and 6.7 h, and S was 13.8 and 6.5 h. G1 was calculated as 13 and 10 h, respectively. These values were determined by labeling cells with (3)H thymidine and measuring the appearance of radioactive mitotic figures. Treatment with 5-fluorodeoxyuridine (FudR) inhibited DNA synthesis and, as a result, cells accumulated in S. Such cells were viable and, upon removal of the FudR, proceeded synchronously into mitosis. Treatment with 5-bromodeoxyuridine, following FudR synchronization, sensitized the cells to white light. Thus cells capable of synthesizing DNA could be killed. 20-30% of the cells in suspension cultures growing at 22 or 33° were not able to synthesize DNA. Nevertheless, these non-dividing (Q) cells were able to synthesize RNA and protein at a reduced rate. The proteins synthesized appear to be a particular subset of the proteins made by normal cells. The results are analyzed in relation to the use of this suspension cell culture system for isolating conditional lethal mutants of plant cells.