Durham, North Carolina
March 8, 2007
A new understanding of how plants
manage their internal calcium levels could potentially lead to
genetically engineering plants to avoid damage from acid rain,
which robs soil of much of its calcium.
"Our findings should help scientists understand how plant
ecosystems respond to soil calcium depletion and design
appropriate strategies to protect the environment," said
Zhen-Ming Pei, a Duke University
assistant professor of biology who led the study, to be
published in the Friday, March 9, issue of the journal Science.
The research was supported by the National Science Foundation,
the U.S. Department of Agriculture and Xiamen University in
China.
Calcium enters plants dissolved within the water that roots take
in from surrounding soil. As the water circulates through a
plant, its dissolved calcium gets shuttled where it is needed to
give the plant's cells their structural rigidity. To grow, a
plant needs a reliable supply of calcium. But calcium supplies
coming into the plant cycle up and down over the course of the
day, dropping to a minimum at night.
Plants use molecular sensors and flows of chemical messengers to
detect and regulate the storage and distribution of vital
nutrients such as water and calcium.
To track the calcium sensors in the model mustard plant
Arabidopsis, the team used molecules originally found in
jellyfish that emit light in response to calcium's presence. To
deduce what the sensor does and does not do, the researchers
also introduced an "antisense" version of the calcium-sensor
protein that abolishes the sensor's effects.
The calcium-sensing molecule in plants, called CAS, was first
identified by Pei's group and described in the Sept. 11, 2003,
issue of the journal Nature. Arabidopsis is favored for such
experiments because it has a relatively short life cycle of
eight weeks and its genome has been completely sequenced.
By tracking the glow of the jellyfish molecules, the researchers
learned that CAS plays a number of roles in plants. The
scientists initially thought it simply monitored changes in
levels of dissolved calcium that enters the plant from the
outside. They discovered instead that CAS also triggers the
release of internal calcium that is stored within the plant via
a chemical signaling system.
This coupled system, the researchers deduce, ensures that
constant levels of calcium remain available to a plant's cells
despite widely varying amounts of the nutrient coming in during
each day and night cycle.
"The sensors try to detect how much calcium is there, and they
coordinate that level with growth and development," Pei said.
"If they detect there is not enough calcium, the plant may elect
to hold off on growth and development until it has more calcium.
The plant may thus appear not to be doing well."
The findings have prompted Pei to begin a new research program
aimed at altering this calcium balancing act to help plants
adjust to the ravages of acid rain.
Produced by interactions between water vapor and human-created
pollutants, acid rain can disrupt plants' calcium balance by
leaching significant amounts of calcium from agricultural and
forest soils as well as from plant leaves, according to Pei.
"It has been found that some soils have lost as much as 75
percent of their calcium during the past century," he said. "One
way to respond is to add new calcium to the soil. But we can't
do that everywhere that it's needed and it is also expensive."
Although acid rain robs soil of much of its calcium, enough is
still left for plants to live on, Pei added. But he suspects
that sensors like CAS may misinterpret "less" as "too little" in
those plants and unnecessarily signal for growth shutdowns.
Perhaps a plant's calcium sensors could instead be tricked into
interpreting "less" as "still enough" and keep building new cell
walls, he suggested.
As a preamble to such genetic engineering, Pei is now leading a
study in his native China that will evaluate the physiology of
various plants affected by acid rain. "It is in the south of
China where acid rain is huge because of industry," he said.
"China is becoming the factory for the United States.
"We will monitor calcium changes in the soil there, and then
clone calcium receptors from various plant species to see
whether those receptors are responsible for growth and how they
respond to acidity," he said. "Some plants grow terribly under
acid rain, but others grow very well."
Other Duke researchers who participated in the current study
were postdoctoral researchers Ru-Hang Tang and Shengcheng Han;
Hailei Zheng, a visiting professor from Xiamen University;
Charles Cook, a laboratory technician; Christopher Choi, an
undergraduate student; Todd Woerner, a chemistry instructor; and
Robert Jackson, a professor of biology and environmental science
and director of Duke's Center on Global Change.
See also:
http://www.nsf.gov/news/news_summ.jsp?cntn_id=108458 |
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