Title:
Scientists Help Cut the Mystery Behind Pruning
Description: This is
a VOA Special English Agriculture Report.
See text below
Text:
We talked last week about when and how to prune
plants. Today we tell you about some new
understanding of why cutting the main branch of a
plant or tree can lead to better development.
The findings are from researchers on two continents.
Professor Prezemyslaw Prusinkiewicz of the
University of Calgary in Canada led the research
with scientists from Britain and Sweden. Their study
appears in the Proceedings of the National Academy
of Sciences.
Researchers have known since the nineteen thirties
that the actively growing tip of a plant releases a
hormone called auxin. This hormone flows down the
main stem. Scientists say the auxin has an indirect
effect on buds on the side of the stem to prevent
branching.These buds themselves also produce auxin.
The research suggests that to grow, they have to be
able to export the hormone into the main stem. But
the flow from the stem tip prevents them from doing
this. The researchers wanted to find out how this
blocking happens.P
rofessor Prusinkiewicz is on sabbatical leave in
Australia, but he sent us an e-mail suggesting a
simple way to understand the process. Think of a
major road crowded with traffic. So many cars are on
the main road that the cars on the side roads cannot
enter.
The stem is like the crowded main road. The new
research shows that the buds on the side cannot
export their auxin into the main stem because it is
too full. But if that main shoot is pruned, other
buds below it can start exporting. They are no
longer inhibited from growing.
Ottoline Leyser from the University of York says
that after a plant is pruned, all the inhibited
shoot tips compete with each other to grow. In doing
this, the branches influence each other's growth.
Nearby shoot tips are more likely to affect each
other than those that are far apart from each other.
Professor Leyser says the strongest branches grow
best, wherever they may be on the plant. The study
found that the main shoot grows the best of all not
because of its position at the top of the plant, but
mostly because it got there first.
And that's the VOA Special English Agriculture
Report. Transcripts and MP3s of our reports,
including last week's advice about pruning, can be
found at voaspecialenglish.com. You can also post
comments. We invite you to share your own
experiences -- good or bad -- with pruning plants
and trees.
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Hi. I
personally reviewed this video and found it appropriate for
the news section of English Global Group. This
is a Voice of America video which covers an interesting
topic in Special English. I would appreciate some feedback from both
students and teachers about this video. You can comment in
the window below using any of a number of different services
including Facebook, Yahoo, AOL, and Hotmail.
