Thought this press release from UW-Madison CALS might interest some
Agricultural and Consumer Press Service
College of Agricultural and Life Sciences
440 Henry Mall
53706 (608) 262-1461
University of Wisconsin-Madison
For Immediate Release
For More Information:
THE LOWDOWN ON POTASSIUM UPTAKE IN PLANTS:
BATTERY-LIKE MECHANISM SHOWS SURPRISING POWER
As gardeners know, potassium is a basic element in plant fertilizers.
Plants fall flat without it. They need potassium to control the
water content of their stems and leaves. Without enough potassium,
plant leaves become limp and cells can't elongate.
Now University of Wisconsin-Madison scientists have shown that plants
can create an electric potential of almost a quarter of a volt across
the cell membrane. That differential allows root cells to draw the
positively charge potassium ions from soil water into the negatively
charged cells. The nutrient moves through special membrane proteins
called potassium channels.
The findings may lead to crops that need less potassium fertilizer,
according to molecular biologist Michael Sussman and plant
electrophysiologist Edgar Spalding. Cell membranes have hundreds of
different proteins that plants use to move compounds across cell
boundaries. Understanding these mechanisms also might lead to crops
that can concentrate other compounds, such as iron, which could help
counter anemia in some countries.
Sussman, Spalding and graduate researchers Rebecca Hirsch and Bryan
Lewis published their findings in the May 8 issue of Science
magazine, which featured a cover photo of one of their plant's roots.
The research is a collaboration between Sussman and Hirsch, from the
Department of Horticulture in the College of Agricultural and Life
Sciences, and Spalding and Lewis from the Department of Botany in the
College of Letters and Science.
"The most startling aspect of the study was how well the uptake
mechanism worked at very low potassium concentrations," Spalding
says. "The magnitude of the electrical gradient allows the channels
to take up potassium at concentrations much lower than scientists
Scientists are more familiar with the electrical gradient and
potassium channels that drive nerve conduction in animals and people.
"The electrical gradient in plants is several times greater than the
one in animal and human nerves," says Sussman. "It allows plants to
take up and concentrate enormous amounts of potassium from soils that
have relatively little of the element."
"Scientists have been unsure just how plants concentrate potassium
from surrounding soils," Sussman says. "Plants have another type of
membrane protein called a high affinity transporter that researchers
thought was more important in taking in potassium. No one thought
potassium channels could function at very low soil potassium levels."
But the UW-Madison researchers showed they could. Working with
Arabidopsis thaliana, a small mustard relative, the scientists
created 14,000 mutant plants. Using a new strategy called reverse
genetics, the team found one plant that contained a defective
potassium channel gene.
By comparing the mutant with plants with a functioning gene, the
researchers could test just how well the potassium channel really
worked in plants. "Important crops may not have the exact same
potassium channel gene as the one in Arabidopsis," Sussman says, "but
crops will have a very similar gene."
Plants have a family of potassium channel genes, he says. By
identifying and testing each separately, researchers can evaluate all
of them with an eye toward developing crops that grow well with less
potassium fertilizer. Scientists have begun similar studies on other
important plant nutrients, according to Sussman.
potassium uptake/plants 9/98
Writer: George Gallepp (608) 262-3636
Press releases from the College of Agricultural and Life Sciences are
available on the Web at
Michele Gale-Sinex, communications manager
Center for Integrated Ag Systems
UW-Madison College of Ag and Life Sciences
Voice: (608) 262-8018 FAX: (608) 265-3020
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