[Cytokinins]

Cytokinins which promote cell division and cell differentiation of plants are structurally classified into two groups: purine-type cytokinins and phenylurea-type cytokinins. Structural modification of the two types led a potent cytokinin, N-(2-chloro-4-pyridyl)-N'-phenylurea (forchlorfenuron). Structure-activity relationship was discussed. The mode of the two types of cytokinins was studied, and a putative receptor which is common to both types was detected using a highly-labelled synthetic cytokinin. Examples of horticultural application of the compound were illustrated.