Cytokinins are a class of phytohormones, signalling molecules specific to plants. They act as regulators of diverse physiological processes in complex signalling pathways. It is necessary for plants to continuously regulate cytokinin distribution among different organs, tissues, cells, and compartments. Such regulatory mechanisms include cytokinin biosynthesis, metabolic conversions and degradation, as well as cytokinin membrane transport. In our review, we aim to provide a thorough picture of the latter. We begin by summarizing cytokinin structures and physicochemical properties. Then, we revise the elementary thermodynamic and kinetic aspects of cytokinin membrane transport. Next, we review which membrane-bound carrier proteins and protein families recognize cytokinins as their substrates. Namely, we discuss the families of "equilibrative nucleoside transporters" and "purine permeases", which translocate diverse purine-related compounds, and proteins AtPUP14, AtABCG14, AtAZG1, and AtAZG2, which are specific to cytokinins. We also address long-distance cytokinin transport. Putting all these pieces together, we finally discuss cytokinin distribution as a net result of these processes, diverse in their physicochemical nature but acting together to promote plant fitness.

• Keywords
• ABCG14, AZG1, AZG2, PUP14, cytokinin distribution, cytokinin hydrophobicity, cytokinin transport, membrane transport,
• MeSH
• Arabidopsis metabolism   MeSH
• Biological Transport MeSH
• Cell Membrane metabolism   MeSH
• Cytokinins metabolism   MeSH
• Homeostasis MeSH
• Hydrophobic and Hydrophilic Interactions MeSH
• Kinetics MeSH
• Plant Roots metabolism   MeSH
• Membrane Transport Proteins metabolism   MeSH
• Arabidopsis Proteins genetics   MeSH
• Gene Expression Regulation, Plant MeSH
• Plant Growth Regulators metabolism   MeSH
• Signal Transduction physiology   MeSH
• Thermodynamics MeSH
• Plant Shoots metabolism   MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Cytokinins MeSH
• Membrane Transport Proteins MeSH
• Arabidopsis Proteins MeSH
• Plant Growth Regulators MeSH