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Pruning: History rather than position gives the main shoot dominance

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22 September 2009

Scientists have shown that the main shoot dominates a plant’s growth principally because it was there first, rather than due to its position at the top of the plant.

Collaborating teams from the University of York in the UK and the University of Calgary in Canada combined their expertise in computational modelling and molecular genetics to make a significant discovery that helps explain why pruning encourages plants to thrive.

The research was funded by the Biotechnology and Biological Sciences Research Council (BBSRC) and the Natural Sciences and Engineering Research Council of Canada (NSERC).

Led by Professors Ottoline Leyser and Przemyslaw Prusinkiewicz and published by the journal PNAS, the research showed that all shoot tips on a plant can influence each other’s growth.

Professor Leyser, of the University of York’s Department of Biology, said: “It is well known that the main growing shoot of a plant can inhibit the growth of the shoots below – that’s why we prune to encourage growth of branches. What we are interested in is exactly how the main shoot can exert this effect.

“It has been known since the 1930s that the plant hormone auxin is released by the plant’s actively growing tip and is transported down the main stem where it has an indirect effect on buds to inhibit branching. There are a number of ways in which the hormone exerts this effect and we have discovered a new path by which it works.”

The research suggests that for a shoot tip to be active, it must be able to export auxin into the main stem. But if substantial amounts of auxin already exist in the main stem, export from an additional shoot tip cannot be established.

Professor Leyser said: “Using this mechanism, all the shoot tips on a plant compete with each other, so that tips both above and below can influence each other's growth. This allows the strongest branches to grow the most vigorously, wherever they may be on the plant. The main shoot dominates mostly because it was there first, rather than because of its position at the apex of the plant.”

The teams went on to show that the recently discovered plant hormone, strigolactone, works at least in part by making it harder to establish new auxin transport pathways from shoot tips, strengthening the competition between auxin sources and reducing branching.

Understanding of the action and interaction of these hormones can inform horticultural practices aimed at changing branching patterns in diverse crops.

The research also involved scientists at the Department of Forest Genetics and Plant Physiology at the Swedish University of Agricultural Sciences.

ENDS

Notes to editors

The paper Control of Bud Activation by an Auxin Transport Switch (manuscript tracking number of 2009-06696R) is available at www.pnas.org/../../recent

About the Department of Biology

The University of York’s Department of Biology is one of the leading centres for biological teaching and research in the UK. In the 2008 Research Assessment Exercise, it was ranked equal first among broad spectrum bioscience departments in the UK for quality that was judged to be world-leading. The Department both teaches degree courses and undertakes research across the whole spectrum of modern biology, from molecular genetics and biochemistry to ecology. Its biomedical research includes an Immunology and Infection Unit (jointly with the Hull York Medical School), work on infertility and 3 research professors funded by Yorkshire Cancer Research and York Against Cancer.

About BBSRC

The Biotechnology and Biological Sciences Research Council (BBSRC) is the UK funding agency for research in the life sciences. Sponsored by Government, BBSRC annually invests around £450 million in a wide range of research that makes a significant contribution to the quality of life for UK citizens and supports a number of important industrial stakeholders including the agriculture, food, chemical, healthcare and pharmaceutical sectors. BBSRC carries out its mission by funding internationally competitive research, providing training in the biosciences, fostering opportunities for knowledge transfer and innovation and promoting interaction with the public and other stakeholders on issues of scientific interest in universities, centres and institutes.

The Babraham Institute, Institute for Animal Health, Institute of Food Research, John Innes Centre and Rothamsted Research are Institutes of BBSRC. The Institutes conduct long-term, mission-oriented research using specialist facilities. They have strong interactions with industry, Government departments and other end-users of their research.

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