Dependence of cytokinin distribution in plants on their physical and chemical properties and transpiration rate

The effect of transpiration on cytokinin accumulation and distribution in 7-day-old wheat ( Triticum durum Desf.) seedlings grown on nutrient medium supplemented with zeatin or its riboside was studied. The content of cytokinins in plants and nutrient medium was measured by the immunoenzyme analysis; cytokinin distribution between root cells was assessed immunohistochemically using antibodies against zeatin derivatives. The rate of transpiration was reduced 20-fold by plant placing in humid chamber. At normal transpiration, after 6 h of plant incubation on the solution of zeatin, the level of cytokinins in plant tissues increased stronger than after incubation on the solution of zeatin riboside (by 7.3 and 3.5 times, respectively, as compared with control), although the rates of both cytokinin uptake were equal. Most portions of cytokinins were retained in the roots, which was stronger expressed in the case of free zeatin uptake. A decrease in the rate of transpiration did not affect substantially the zeatin absorption from nutrient medium and the total level of cytokinin accumulation in plants, but these indices were sharply decreased in the case of zeatin riboside. In the zone of absorption of both control roots and roots treated with cytokinins, more intense cytokinin immunostaining was observed in the cells of the central cylinder. The interrelation between cytokinin distribution between the cells and apoplast, their inactivation, and transport over the plant and their form (zeatin or zeatin riboside) used for treatment is discussed.