Shoot branching increases the photosynthetic surface area and the points at which reproductive structures can form. In angiosperms, auxin (specifically, auxin depletion) has been shown to be involved in the initiation and outgrowth of shoot branches. For example, in apical dominance the primary shoot meristem suppresses bud outgrowth by producing auxin; when the source of the auxin is removed by decapitation, side branches can grow out. Harrison compares the contribution of auxin and auxin transporters in shoot branching in angiosperms as well as other vascular plants, bryophytes, and fossil plants. She concludes that “divergent auxin transport pathways were recruited to regulate branching in plant gametophytes and sporophytes during evolution”. New Phytol.
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