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Apical dominance maintained by sugar limitation

QAAFI Science Seminar, Tuesday 15 April 2014 Prof. Christine Beveridge Professor / ARC Future Fellow The University of Queensland ABSTRACT Vigorously growing shoot tips can maintain dominance over the growth of axillary buds in a process termed apical dominance. In this seminar we show that the shoot tip, which is a hungry consumer of mobile sugars, acts to prevent the growth of axillary buds by affecting the levels of sugars left over for the buds. Mobile photoassimilates/sugars move rapidly; 150 cm per hour in tall garden pea plants. After decapitation, the enhancement in photoassimilate supply occurs at a rate of about 0.5 cm per minute and correlates with the timing of bud outgrowth. Exogenous sucrose can induce bud release in intact plants in a dynamic response similar to decapitated plants. Sucrose induces the same transcription factor in buds previously reported to be regulated by plant hormones to control bud outgrowth (BRC1, BRANCHED1). In contrast, auxin moves at 1 cm per hour and too slowly to induce the early growth of axillary buds at a distance. Treatments that reduce auxin content do not lead to bud release unless sugars are also increased by these treatments. Sucrose is therefore both necessary and sufficient to induce bud release. Auxin treatment to the cut surface of decapitated shoots does not prevent the early growth of buds and an auxin transport inhibitor supplied directly to axillary buds of decapitated plants also fails to prevent early bud outgrowth. This discovery published in PNAS establishes a different paradigm for apical dominance, namely that sugar supply has an important regulatory role in the initial release of buds for growth and that the classical plant hormones, auxin, strigolactone and cytokinin gain in importance once this release has occurred. The role of hormones in controlling source-sink relationships and of sugars in affecting meristem development will be important to introduce or highlight in future research on shoot architecture and plant development more generally. More info: http://www.biology.uq.edu.au/staff/ch...