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PARTICIPATION OF ENT3 TRANSPORTER IN CYTOKININ DISTRIBUTION BETWEEN THE ROOT AND THE SHOOT AND IN REGULATION OF GROWTH RESPONSE OF ARABIDOPSIS PLANTS TO INCREASED LEVEL OF MINERAL NUTRITION

The nitrogenous base riboside transporter ENT3 is known for its ability to transport ribosylated cytokinins across the membrane. However, its role in the distribution of cytokinins between plant organs has not yet been studied. For this purpose, we compared the content and distribution of either endogenous cytokinins or the exogenous trans-zeatin riboside introduced into the nutrient solution in mutant ent3-1 plants and the parent genotype Columbia. In the mutant, the accumulation of endogenous cytokinins in the roots was suppressed, and the ability to deliver exogenous trans-zeatin riboside to shoots increased. The roots of ent3-1 were about 15% longer and had a lower cytokinin concentration. A thirtyfold increase in the concentration of macronutrients led to inhibition of root elongation in the original Columbia line, but not in ent3-1 plants. This growth response occured in accordance with the content of cytokinins in the roots: in Columbia plants, cytokinins accumulated in these organs. The increase in the level of hormones in the roots of ent3-1 was to a lesser extent and was not significant. It was concluded that the ENT3 transporter is involved in the distribution of endogenous cytokinins between the apoplast and symplast, facilitating their uptake by root cells, thereby limiting the export of cytokinins to shoots through the xylem, and can play an important adaptive role in changing the level of mineral nutrition.