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Plant math: Why roots grow down, not up

U. NOTTINGHAM (UK) — Using new technology and math modeling, researchers have discovered how plant roots know to grow down and not up in order to explore the soil and maximize water uptake.

“This research really demonstrates the value of an interdisciplinary approach to plant science questions. By combining the skills of mathematical modelers with experimental biologists we have a new range of tools with which to investigate root growth,” says Malcolm Bennett, professor in plant science at the University of Nottingham and biology director of the Center for Plant Integrative Biology.

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Scientists have long speculated that plants bend in response to gravity due to the redistribution of the plant hormone auxin in the tip of the root.

The new study, published in Proceedings of the National Academy of Sciences, combines the newly developed DII-VENUS technology—another collaborative research project involving the University of Nottingham—with mathematical modeling to demonstrate that auxin does indeed redistribute when roots are turned through 90 degrees, but far faster than previously thought.

The study shows that auxin is redistributed to the lower side of a growing root within minutes of the root being turned through 90 degrees. It also shows that this gradient is rapidly lost as bending root tips reach a tipping point at an angle of 40 degrees to the horizontal. The formation and loss of the auxin gradient serves as an “on” and “off” switch for the root bending response.

The auxin sensor DII-VENUS, recently detailed in the journal Nature, was used in conjunction with a parameterized mathematical model to provide a high-resolution map of hormone distribution through time.

More news from University of Nottingham: http://communications.nottingham.ac.uk/News.html

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