Tracking the Story of Cytokinin Research

Existence of compound(s) inducing cell division in excised plant tissues was spotted more than 100 years ago. Since then research of cytokinins (CKs), plant hormones which in cooperation with other phytohormones, namely auxin, control cytokinesis, and a number of other physiological processes in plants, has advanced correspondingly to the progress in other fields of life sciences. This historical overview is focused on major topics of CK research including (1) discovery of CKs, (2) search for natural CKs, (3) role of CKs in transfer RNA, (4) biosynthesis (5) metabolism, (6) signaling of CKs, and (7) molecular probing of the physiological functions of CKs. Some parts of these subjects can already be assessed within the context of an appropriate time span necessary for critical evaluation. I have used this opportunity to present also some personal recollections, namely those of Prof Folke Skoog, in whose laboratory the first CK, kinetin, was discovered.