Hormone’s effect on plant growth studied

CONTACT: B.J.
Almond
PHONE: (713) 348-6770
EMAIL: balmond@rice.edu

HORMONE’S
EFFECT ON PLANT GROWTH STUDIED
Rice University biologist hopes findings
about auxin will be useful to agriculture

A Rice University
biologist’s genetic research on a weed hormone might lead to a better
understanding of how that hormone affects plants that humans rely on for food
and fiber.

Bonnie Bartel, assistant
professor of biochemistry and cell biology, is trying to figure out how levels
of the hormone auxin are regulated in the plant Arabidopsis thaliana. This weed
is ideal for genetic research because its generation time is only six weeks and
all 25,000 of the genes in its genome have been sequenced.

Auxin causes plants to
bend toward light and also promotes root development. The latter function is
what Bartel’s research group observes to identify mutant plants, because they
tend to sprout irregular roots.

“Our approach is to look
for mutant plants that are defective in various aspects of the metabolism of
auxin,” Bartel said. “Those mutants allow us to identify defective genes, which
in turn helps us identify the enzyme made by those genes that is important for
auxin metabolism.”

But the process is
time-consuming and tedious. To isolate the mutants, researchers grow tens of
thousands of seed on a solution that contains either auxin or an auxin
precursor, a chemical that the plant normally converts to auxin. After eight
days, the plants have grown enough for their roots to be inspected. The
researchers have to eye each of the plants in search of mutants that reveal a
defect in the gene that converts the precursor to the hormone. Seeds from the
mutants can be used to grow plants for further study.

“It can take several
years to identify the gene that is defective,” Bartel said. “Once we know which
gene is defective, we study where in the plant that gene is expressed, and then
we study biochemically what the protein encoded by that gene
catalyzes.

“We would like to
understand all the inputs and outputs of the auxin pool in the plant and how the
plant regulates them, because this hormone controls the size of cells,” she
added.

Because Arabidopsis
thaliana is closely related to other flowering plants, Bartel is hopeful that
what she learns about hormone regulation will be useful to
agriculture.

Her work is supported by
the National Institutes of Health, the National Science Foundation, the U.S.
Department of Agriculture and the Robert A. Welch
Foundation.