The class of plant hormones cytokinins is central to the regulation of many physiological processes including cell division, cell differentiation, organ formation, nutrient partitioning and senescence. We have identified a cytokinin receptor. Receptors cannot be ignored when one discusses signal transduction of cytokinins and cytokinin-related physiological processes.

  Does it describe a new discovery or new methodology that's useful to others?

Yes, I think so. The outline of the whole cytokinin signaling system will soon be uncovered and web of signaling of multiple plant hormones will also be a major topic.

For such studies, cytokinin-related mutants and transgenics should be useful. Also genes for cytokinin receptors are potentially useful to improve crops.

When a callus, an un-differentiated mass of plant cells, is cultured in the presence of cytokinins, it forms buds and leaves. We simply thought this response interesting, and decided to identify cytokinin-response mutants in tissue culture. One of such mutants led us to the identification of a cytokinin receptor.

Cytokinins are a class of classical plant hormones, but until recently they had been the least understood class. Identification of the receptors by us and recent findings of downstream signaling components by others allowed us to draw a good picture. The emerging picture is that cytokinins are perceived by trans-membrane histidine kinases and the information transduced through phosphorelay, which in turn activates transcription factors. I believe that this picture will be elaborated and extended in the near future.

Dr. Tatsuo Kakimoto
Dept. of Biology
Graduate School of Science
Osaka University
Machikaneyama 1-1
Toyonaka, Osaka 560-0043, Japan