Cytokinin oxidase: new insight into enzyme properties

The cytokinin group of plant hormones plays an essential role in the regulation of plant growth and differentiation, including the release of lateral buds from apical dominance and the delay of senescence [1] and [2]. Moreover, increasing evidence supports the hypothesis that cytokinins interact with auxins at multiple levels in a complex manner to control various physiological and developmental responses3. However, in spite of their fundamental role, our understanding of the molecular mode of action of cytokinins and of their metabolism remains rather rudimentary. In particular, the enzymes involved in the control of the cytokinin cell cycle have been poorly characterized