With Green Beans, Less Water Means More
Calcium
By Jim De
Quattro
November 17, 1999 Some green beans outdo others as a
source of bone-building calcium. The difference, according to researchers, can
depend on how much water flows through the plants.
When it comes to getting calcium from the diet, most people think first of
milk. But green beans are good sources too. Scientists at the
Children's Nutrition Research Center
in Houston, Texas, compared calcium content in six bean varieties. The top
performer, Hystyle, was also the stingiest water user.
The Houston center is a joint venture of
Baylor College of Medicine and
the Agricultural Research Service, USDA's
chief scientific agency. The Houston scientists focus on how foods can better
nourish children--and new mothers and their babies.
Calcium is especially important for children when their bones are growing.
Dairy products are excellent calcium sources. Beans and other veggies can also
provide a substantial portion of requirements. And these foods could play a
bigger role for children who can't tolerate milk sugar.
In the Houston study, the Hystyle green beans had about double the calcium
content of a variety called Labrador. The reason? Hystyle is better at
conserving water, according to plant physiologists Michael Grusak and Kirk
Pomper.
Water dilutes calcium moving through a bean plant, reducing the amount
reaching pods. Tiny pores called stomates open and close to control the speed
at which water enters and leaves a plant. This action is genetically and
environmentally controlled.
Overall transpiration in Hystyle was about half that of Labrador. The lower
transpiration meant higher calcium concentrations in Hystyle's xylem stream.
The xylem transports liquid and mineral nutrients from roots to shoots,
somewhat as a person's arteries carry oxygen-rich blood.
A story about the research appears in the November issue of Agricultural
Research magazine and on the web at:
http://www.ars.usda.gov/is/AR/archive/nov99/beans1199.htm
Scientific contact: Michael A. Grusak,
ARS Children's Nutrition Research
Center, Baylor College of Medicine, Houston, Texas, phone (713) 798-7044, fax
(713) 798- 7078, mgrusak@bcm.tmc.edu.
|
