Herbicide may affect plants thought to be resistant

ScienceDaily (Nov. 22, 2011) ? Purdue University researchers have discovered a fine-tuning mechanism involved in plant root growth that has them questioning whether a popular herbicide may have unintended consequences, causing some plants to need more water or nutrients.

Angus Murphy, a professor of horticulture, and Wendy Peer, an assistant professor of horticulture, study the movement of auxin, a plant hormone essential for plant development. They showed that ABCB4, a protein responsible for moving auxin into cells, also removes the hormone when too much has accumulated.

"We knew that the protein took auxin up, but found that it switched to removing auxin when a threshold is reached," said Murphy, whose findings appeared in the early online version of The Plant Journal. "It starts transporting the hormones out."

That fine-tuning mechanism is integral to proper development of plant root hairs, which extend from the main plant root and are where most water and minerals enter.

"The root hairs are doing all the heavy lifting for bringing the water into the plant," Peer said. "And ABCB4 maintains the right auxin levels to keep root hairs growing optimally."

The herbicide 2,4-D, a synthetic form of auxin, could have unintended consequences for the protein, Murphy and Peer said.

The herbicide is used to kill broadleaf weeds, which are dicots, while monocot grasses, such as sorghum and corn, are more resistant. That's because grasses inactivate 2,4-D inside the plant, while broadleaf dicots do not.

But ABCB4 is located on the root surface and can be switched into intake-only mode, disabling its ability to remove excess auxin from cells, before 2,4-D can be inactivated inside the plant. This results in shorter root hairs.

"This suggests that ABCB4 is an unexpected target of 2,4-D action," Murphy said. "It's something that we have to be aware of with the commercial introduction of 2,4-D resistant soybeans and other dicot crops."

Murphy said laboratory testing of ABCB4 in yeast, tobacco and human cells subjected to 2,4-D all showed that ABCB4 could be locked into the uptake-only mode. The root hairs of mutant plants that had ABCB4 removed were not affected by application of 2,4-D.

"It was very clear that what was happening in the plant was what was happening in the cell cultures," Murphy said.

Murphy said the findings suggest that application techniques that limit 2,4-D entry into soils are important to ensure that production with engineered 2,4-D resistant crop plants does not require additional fertilizer and/or water inputs.

The Department of Energy funded the study. Murphy and Peer partnered with scientists at the Institute of Experimental Botany at the Academy of Sciences of the Czech Republic.

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Story Source:

The above story is reprinted from materials provided by Purdue University. The original article was written by Brian Wallheimer.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

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Journal Reference:

1. Martin Kube?, Haibing Yang, Gregory L. Richter, Yan Cheng, Ewa M?odzi?ska, Xia Wang, Joshua J. Blakeslee, Nicola Carraro, Jan Petr??ek, Eva Za??malov?, Kl?ra Hoyerov?, Wendy Ann Peer, Angus S. Murphy. The Arabidopsis Concentration-Dependent Influx/Efflux Transporter ABCB4 Regulates Cellular Auxin in the Root Epidermis. The Plant Journal, 2011

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

Source: http://feeds.sciencedaily.com/~r/sciencedaily/~3/TunL7spH5nQ/111122133318.htm

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