Extra- and intracellular distribution of cytokinins in the leaves of monocots and dicots

• Plant hormones cytokinins are distributed unequally within the cellular compartments and in the cell exterior of the leaf.
• Monocot and dicot plants show significant differences in cytokinin metabolite composition.
• Overall cytokinins content in vacuoles that were previously considered storage organelles is rather low.
• Genetic manipulation of the cytokinin metabolism induces complex changes in the distribution of individual forms of the hormone in order to keep homeostatic balance.

The plant hormones cytokinins are a convenient target of genetic manipulations that bring benefits in biotechnological applications. The present work demonstrates the importance of the subcellular compartmentalization of cytokinins on the model dicot plant Arabidopsis thaliana and monocot crop Hordeum vulgare. The method of protoplast and vacuole isolation combined with precise cytokinin analysis and recovery assay of a vacuolar marker protein were used to quantify the contents of individual cytokinin forms in the leaf extracellular space, cell interior and vacuole. The data obtained for wild type plants and in each case a specific mutant line allow comparing the effect of genetic manipulations on the hormone distribution and homeostatic balance of cytokinins in the modified plants.