Studies on the control of mitotic activity in excised roots. I. The experimental system.

The mitotic characteristics of excised roots of the garden pea, Pisum sativum, have been studied under conditions of controlled nutrition. The excised root system was tested with regard to its ability to respond, mitotically, to various carbon sources. Sucrose, glucose, fructose, and DL-glyceraldehyde were found to support mitotic activity in excised roots, galactose and 2-deoxy-D-glucose were toxic, and mannose ineffective. Initiation of mitotic activity in the presence of glucose was inhibited by the respiratory poisons, KCN and malonic acid, the uncoupling agent, 2,4-dinitrophenol, but was not notably affected by the protein synthesis inhibitor, chloramphenicol. The glucose-induced response in mitotic activity was not affected by the carcinogen, urethan, and indeed, there is some evidence that the response was actually enhanced. The fact that KCN, malonic acid, and probably 2,4-dinitrophenol, in suitable concentrations inhibit the onset of cell division suggests that some level of operation of the Krebs' cycle is essential for commission of cells into mitosis. Likewise, failure to inhibit cells in the process of active mitosis by KCN and malonic acid is not inconsistent with the idea that there is a shift from reliance on aerobic to anaerobic respiration between antephase and active mitosis.