The interplay between cytokinins and light during senescence in detached Arabidopsis leaves

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. The manuscript demonstrates the importance of light in balancing the cytokinin homeostasis during senescence of detached leaves and reveals that light is able to compensate the disrupted cytokinin signalling in cytokinin receptor double mutants. The cytokinin‐dependent regulation of lipid peroxidation and the regulation of the functionality of photosynthetic apparatus seem to be primarily mediated via different cytokinin receptors (AHK4 and AHK3, respectively). On the basis of our results, we present a scheme summarizing the role of light, cytokinin receptors, and the main active forms of cytokinins in the regulation of senescence in detached leaves.