November, 1999
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USDA-ARS
plant physiologist
Michael Grusak examines roots
of hydroponically grown
green bean plants.
Photo by Jack Dykinga. |
Drink your beans!
Reprint from the November 1999
issue of
Agricultural Research
magazine
Calcium, that bone-building
nutrient so important to growing kids, can't always come from
cows. For example, dairy products won't do as a calcium source
for children who can't tolerate lactose—milk sugar.
Green beans are also a good source of calcium, and some beans
are better than others.
 Plant
physiologists Michael Grusak and Kirk Pomper, who are
with the Children's Nutrition Research Center at
Houston, Texas, evaluated six bean varieties for calcium
content.
A variety named
Hystyle had about twice the calcium as the Labrador
variety, and these researchers figured out why:
Hystyle
is better at conserving water.
Water dilutes the calcium
moving through a bean plant, reducing the amount reaching the
pods that people eat.
The Houston center is a joint venture of Baylor College of
Medicine and USDA's
Agricultural Research Service.
Many ARS scientists study how nutrients feed plants, so yields
can be raised. At Houston, Grusak focuses on how crops can feed
people better.
Calcium is especially important for
children when their bones are growing. Other research at the Houston
center suggests bone weakness later in life may be related to how
much calcium children get during growth phases in childhood and
adolescence.
The speed at which water
gets in and out of a plant depends largely on how quickly it is
transpired from leaves and other surfaces. The opening and closing
of tiny pores called stomates regulate transpiration. The action is
both genetically and environmentally controlled.
"We found the whole-plant transpiration rate to be twice as high in
Labrador as in
Hystyle, even though the amount of water transpired from
the pod itself is the same for both," says Grusak. The researchers
found that the higher transpiration rate in Labrador plants resulted
in lower concentrations of calcium moving in the plant's xylem
stream.
Xylem transports liquid
and nutrients throughout the plant, somewhat as arteries in a
person carry oxygen-rich blood.
Green
beans like
Hystyle could also be good news for farmers and
environmentalists. These beans require less water, so they
reduce irrigation costs.
Taking less water from area lakes, streams, or aquifers helps
the environment in two ways. It conserves water in drier areas,
and it reduces the amount of farm chemical runoff going back
into the environment
By Jill Lee,
formerly with ARS.
This
research is part of Plant Biological and Molecular
Processes, an ARS National Program (#302) described on
the World Wide Web at
http://nps.ars.usda.gov/programs/cppvs.htm.
Michael A. Grusak (mgrusak@bcm.tmc.edu)
is with the USDA-ARS
Children's Nutrition Research Center,
1100 Bates St., Houston, TX 77030; phone (713) 798-7044,
fax (713) 798-7078.
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