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Why pruning encourages plants to thrive


September 28, 2009
By Marg Land


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pruningtreesSeptember 28, 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.



September 28, 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 United Kingdom and the University of Calgary in
Canada combined their expertise in molecular genetics and computational
modelling to make a significant discovery that helps explain why pruning
encourages plants to thrive.

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

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.

“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,” said Professor Leyser, of
the University of York’s Department of Biology. “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.

“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,” said Professor Leyser. “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.

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