Relative Activities of Some Cytokinin Fractions of Developing Cotton Fruit

Ion-exchange fractionization, paper chromatography, and soybean callus bioassay have partly resolved an apparent discrepancy in the sequence of cytokinin appearance in developing cotton (Gossypium hirsutum L.) fruit compared to the sequence reported in corn (Zea mays L.). Cotton fruit cytokinins were separated into three fractions: A combined n-butanol and ethylacetate extractable fraction comprisedc. 10% of the cytokinin activity, a fraction not retained by a polymethacrylate weakly acidic cation-exchange resin comprised c. 45%, and a fraction that was retained by the resin, c. 45%. The latter fraction differs from cytokinin fractions reported in corn. However, like cytokinin ribonucleotides, its cytokinin activity remains below R_f 0.3 on paper chromatograms developed with water-saturated sec-butanol, thus complicating studies of sequential cytokinin appearance in cotton. An anion-exchange resin did not retain the cytokinin activity of this fraction.