The use of dimethylsulfoxide as a solvent in the tobacco bioassay for cytokinins.

The use of dimethylsulfoxide as a solvent for synthetic purine and urea derivatives in the tobacco callus bioassay for cytokinin activity (10) has simplified the test procedure at two stages. First, the high solubility of these compounds in DMSO' has made it possible to test the less active materials, or those which are only slightly water-soluble, through a wide range of concentrations; secondly, full strength DMSO stock solutions act as sterilizing agents. Test compounds in DMSO solutions can be added directly to the cooling agar medium after autoclaving, thus avoiding destructive heating, and reducing the work, time, and equipment needed for the bioassay. In this laboratory DMSO was first employed as a solvent in the bioassay of diphenylurea. Bruce and Zwar (1) have reported the