Biomics

Presence of cytokinins both in xylem and phloem saps suggests involvement of these hormones in long distant signaling. Root-to-shoot cytokinin transport is well documented, however, much less is known about shoot-to-root transport. In the present study we followed concentration of free cytokinin bases and ribosides in the phloem sap (leaf diffusate) after incubation of leaves in a solution supplemented with either zeatin or isopentenyladenine. Different procedures of fixation were used to conjugate either cytokinin bases or their ribosides to proteins of cytoplasm to enable visualization of the differential localization of these cytokinins in the leaf cells of plants. In vivo localization shows the presence of ribosylated forms of cytokinins in leaf vascular bundles. This suggests that conversion of zeatin to its riboside is important for the shoot-to-root transport of zeatin-type cytokinins. Exogenous isopentenyladenine was not modified, but diffused from the leaves as free base. Although these metabolic differences may be not universal and may depend on the plant species and age, our data show that measurements of accumulation and distribution of cytokinins between the leaf cells after specific fixation of either free cytokinin bases or their ribosylated forms may be a valuable source of information concerning cytokinin metabolism and transport.

immunolocalization, cytokinin metabolism and transport, phloem, Triticum durum

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