title: Canopy light gradient perception by cytokinin.
abstract: We have recently identified cytokinin as an important xylem-carried signal involved in the photosynthetic acclimation of plants to light gradients in dense canopies. Lower leaves become shaded in a dense canopy and consequently have reduced transpiration rates. our measurements have shown that this results in a reduced delivery of cytokinins carried in the transpiration stream to shaded leaves, as compared to light-exposed leaves. Cytokinins are involved in the regulation of photosynthetic acclimation to the light gradient by stimulating the expression of photosynthetic enzymes in light-exposed leaves. In shaded leaves, the low delivery rate of cytokinin leads to reduced photosynthetic capacity and ultimately senescence. We show evidence for this role of cytokinin, as part of a complex of signaling pathways where other regulatory mechanisms are also involved. A model is presented depicting the regulation of photosynthetic acclimation by cytokinin delivery to leaves dependent on the irradiance they receive.
authors.affiliation: Plant Ecophysiology Group; Institute of Environmental Biology; Utrecht University; Utrecht, The Netherlands.
authors.forename: Alex
authors.initials: A
authors.lastname: Boonman
authors.forename: Thijs L
authors.initials: TL
authors.lastname: Pons
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