Abstract
Cytokinins are plant hormones that may play essential roles in various aspects of plant growth and development. Although functional significance of exogenous cytokinins has been documented well, the precise role of endogenous cytokinins has remained largely unknown. To gain insight into the molecular function of cytokinins, we carried out a series of phenotypic analysis using a set of mutants carrying lesions of the cytokinin receptor genes, AHK2, AHK3, and AHK4. The ahk2 ahk3 double and ahk2 ahk3 ahk4 triple mutants exhibited semi-dwarf phenotype in shoot and severe growth defects in shoot and roots, respectively. The inhibition of the growth was associated with the reduced meristematic activity of cells, suggesting that the primary function of AHK genes as well as cytokinins is activation and maintenance of cell division activity during organogenesis. AHK2 and AHK3 are expressed ubiquitously, suggesting the housekeeping roles of both genes in plant grouth and development.
