Drought effects on the tissue- and cell-specific cytokinin activity in poplar

Cytokinins are important phytohormones that regulate plant growth. Here we localized cytokinin activities in poplar trees, which are important biomass crops. We demonstrated that even mild drought stress strongly suppresses cytokinin activities in the cambium, the "stem cells" of trees, resulting in loss in productivity and reduced wood formation. Cytokinin activities also decline in the leaf stalks before shedding. Our results identified critical tissues for drought acclimation in the woody biomass crop poplar and provide a basis for selection of climate-smart trees.