[Modern aspects of studying phytohormones. Cytokinins]

The review presents current data on mechanisms of cytokinin action in plants. By analogy with the first part (Ivanova et al., 1999), in which general principles of phytohormone action and cardinal trends of phytohormone investigations were examined, here the relevant information on mechanisms of action of auxins and gibberellins has been given, and taking cytokines as example an attempt has been done to summarize the literature data on the number of questions offered for analysing hormones of high animals (Gudwin, Merser, 1986). The review demonstrates that mechanisms of cytokine action at the cellular level are not known in many cases. One of the most significant factors in the action of phytohormones of this class on plants is their concentration, determined by their synthesis, transportation and further chemical conversions. This paper points to a poor knowledge of the relative role of these processes in regulation of cytokinin contents and their distribution among plant organs. Two possible ways of studying cytokinin action at the present day stage of investigations have been designated: 1) revealing the cytokinin expressed genes and establishing mechanisms of their action; 2) estimation of endogenous cytokinin alteration and the influence of this alteration on definite processes in the cell with the help of ipt-gene from t-DNA of Agrobacterium tumefaciens.