Light and cytokinins are known to be the key players in the regulation of plant senescence. In detached leaves, the retarding effect of light on senescence is well described; however, it is not clear to what extent is this effect connected with changes in endogenous cytokinin levels. We have performed a detailed analysis of changes in endogenous content of 29 cytokinin forms in detached leaves of Arabidopsis thaliana (wild-type and 3 cytokinin receptor double mutants). Leaves were kept under different light conditions, and changes in cytokinin content were correlated with changes in chlorophyll content, efficiency of photosystem II photochemistry, and lipid peroxidation. In leaves kept in darkness, we have observed decreased content of the most abundant cytokinin free bases and ribosides, but the content of cis-zeatin increased, which indicates the role of this cytokinin in the maintenance of basal leaf viability. Our findings underscore the importance of light conditions on the content of specific cytokinins, especially N6 -(Δ2 -isopentenyl)adenine. On the basis of our results, we present a scheme summarizing the contribution of the main active forms of cytokinins, cytokinin receptors, and light to senescence regulation. We conclude that light can compensate the disrupted cytokinin signalling in detached leaves.

Centre of the Region Haná for Biotechnological and Agricultural Research Department of Biophysics Faculty of Science Palacký University 78371 Olomouc Czech Republic

Laboratory of Growth Regulators Faculty of Science Palacký University and Institute of Experimental Botany AS CR 78371 Olomouc Czech Republic

Laboratory of Growth Regulators Faculty of Science Palacký University and Institute of Experimental Botany AS CR 78371 Olomouc Czech Republic Centre of the Region Haná for Biotechnological and Agricultural Research Department of Chemical Biology and Genetics Faculty of Science Palacký University 78371 Olomouc Czech Republic

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