Drink Your Beans!
Plant physiologist Michael Grusak examines roots of hydroponically grown green
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 lactosemilk sugar.
Green beans are also a good source of calcium, and some beans are better
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
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
Green beans like Hystyle could also be good news for farmers and
environmentalists. These beans require less water, so they reduce irrigation
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
Michael A. Grusak is with the
USDA-ARS Children's Nutrition Research
Center, 1100 Bates St., Houston, TX 77030; phone (713) 798-7044, fax (713)
"Drink Your Beans!" was published in the
November 1999 issue of
Agricultural Research magazine.