An improved cytokinin bioassay using cultured soybean hypocotyl sections

This paper describes a modified soybean (Glycine max) tissue culture bioassay for cytokinins. Soybean hypocotyls were grown under sterile conditions and sliced into 1-mm sections. Sections were cultured for 5,9,13, or 22 days on a callus medium with zeatin or other cytokinins. The fresh weight of sections increased with the cytokinin concentration from 0.0005 to 1 mum zeatin; 2-fold concentration differences were readily distinguishable at 9 days. The assay should prove to have several advantages over the conventional soybean callus bioassay including convenience, lower variability between tissue samples, and improved resolution. Its specificity is comparable to that of the soybean callus bioassay.