Thursday, 14 November 2013 00:00

Pass the Salt— The Molecular Mechanism that Drives Halotropism

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sorghumSorghum turns its roots
away from salt through a
protein called PIN2.
Remember that second-grade science project when you watched bean plants grow toward a light source? Little did you know, you were researching heliotropism. Tropism in plants is turning toward or away from a stimulus such as sunlight, gravity, or water. And now there's a new tropism to investigate, although not for second graders. Carlos Galvan-Ampudia and Christa Testerink at the Swammerdam Institute for Life Sciences in Amsterdam and colleagues have found the molecular mechanism behind halotropism, the movement of plants roots to avoid saltiness. Their findings on tropism in Arabidopsis, tomato, and sorghum roots appeared in October's Current Biology.1

The researchers determined that roots are able to move against gravity and away from high salt due to a hormone called auxin that coordinates cell growth and development. When the plant's roots come in contact with a salty environment, the auxin goes to the non-salty side. They looked closer to see what was going on in the root cells exposed to salt solution. It turns out that the salt activates an enzyme (phospholipase D), which leads to a protein (PIN2) that normally sits at the surface cells to be collected in tiny bubbles within the cell. The movement of PIN2 away from the surface causes auxin to move from the salty side of the root to the non-saline side. PIN2 was previously shown to be important in response to gravity (gravitropism), which suggests that PIN2 may be important for plants' response to environmental cues.

1Galvan-Ampudia CS, Julkowska MM, Darwish E, Gandullo J, Korver RA, et. al. (2013) Halotropism is a response of plant roots to avoid a saline environment. Curr Biol. Oct 21;23(20), 2044-2050. doi: 10.1016

Christina Szalinski

Christina is a science writer for the American Society for Cell Biology. She earned her Ph.D. in Cell Biology and Molecular Physiology at the University of Pittsburgh.

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