Their finding, published in the July 11, 2003, issue of the journal Cell, is a major step forward in understanding plant fertility. The discovery could also help researchers understand similar biological processes, such as now nerve cells find each other and make appropriate connections. It may even provide clues about repairing spinal cord injuries.
"Since agriculture, which supplies nearly 80 percent of the world's food supply, depends so profoundly on plant fertility, understanding this process is fundamentally important," said Daphne Preuss, Ph.D., professor of molecular and cell biology and an investigator in the Howard Hughes Medical Institute at the University of Chicago.
When a pollen grain is deposited on the surface of a flower, it somehow has to grow a tube from the stigma of the flower, past several different cell types to where the eggs are, digesting tissue as it grows to burrow all the way inside. "While a few molecules involved in this process have been identified over the years," said Preuss, "we really still don't understand how this tube gets from start to finish."
Working with Arabidopsis, a popular model plant, Preuss and colleagues from her lab found that plants produce a carefully controlled gradient of gamma-amino butyric acid (GABA), a molecule best known for its role in the mammalian nervous system, to lure a pollen tube toward the egg cells. GABA acts like a light at the end of a tunnel, stimulating the initial growth of the pollen tube and shining ever brighter as the tube gets closer to its goal.
The researchers found that the key to regulating GABA levels is an enzyme they named POP2 that degrades GABA. A
Contact: John Easton
University of Chicago Medical Center