CYTOKININ-BINDING PROTEIN FROM MAIZE SHOOTS

Zeatin binding sites have been detected in soluble protein extracts of 5-day-old etiolated maize shoots. Gel filtration on Sephacryl S200 showed a single binding peak of Mr ∼ 45 kDa. The binding protein was purified approximately 500-fold by anion exchange, gel permeation and high performance anion exchange and hydrophobic interaction chromatography. SDS-PAGE revealed a major polypeptide of Mr∼46 kDa, corresponding to the molecular size of the major binding peak from gel permeation. Zeatin binding varied with ionic strength, but could be detected using both precipitating (ammonium sulphate assay) and non-precipitating (equilibrium dialysis) conditions. Scatchard analysis of ammonium sulphate assay data suggested at least two sets of high affinity sites, with kd values of 11.5 nM and 240 nM. Among various cytokinin analogues and other growth regulators, only active cytokinins competed effectively with 3H-zeatin for binding. In addition, adenosine-5'-triphosphate, but not other nucleoside triphosphates, displaced 3H-zeatin. © 1990, Gustav Fischer Verlag, Stuttgart. All rights reserved.