Amino Acid Proves Key to Plant Reproduction. (Down the Tubes)
Travis, J., Science News
Scientists have discovered that one of the myriad signals that human brain cells use to communicate also enables flowering plants to have sex. This versatile substance, an amino acid known as amino butyric acid or GABA, appears to help pollen grains form the sperm-carrying tubes that snake their way to a flowering plant's eggs.
GABA's new role came to light as Daphne Preuss, a Howard Hughes Medical Institute investigator at the University of Chicago, and her colleagues studied a sterile mutant strain of the mustard weed Arabidopsis thaliana, a small flowering plant that serves as a model of plant biology for many scientists.
In normal strains of the plant, pollen grains settle on a flower's stigma and germinate, sending out tubes that burrow through various tissues before each tube makes its way to an ovule--one of many egg-bearing regions in a flower's ovary. The tubes are "very precise and orderly. It's a beautiful process," says Preuss.
In the sterile strain, pollen tubes either stall in their journey or go astray. "They're just meandering everywhere," says Preuss.
In the July 11 Cell, she and her colleagues chronicle how they traced this oddity to a mutation in the gene for a protein belonging to a family of enzymes that modify amino acids. Curious about the enzyme's normal target, they next analyzed the amino acid content of flowers from the mutant strain and found that GABA's concentration was 100 times normal. The enzyme apparently speeds the degradation of GABA under normal conditions, so GABA builds up inside mutant plants that lack the enzyme. …