cytokinin

A naturally occurring biochemical (or closely related group of biochemicals) in plants, sometimes called a plant growth substance, plant regulator or plant hormone. Cytokinins are made in the roots and are transported in the xylem towards the shoot apices, where they promote cell division and the growth of lateral shoots, regulating apical dominance in concert with auxin.

This definition is abridged from A – Z of tree terms: A companion to British arboriculture.
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