Carbon is the key

In a subsequent series of experiments, Brawley, Pearson and Serrao delved into the biochemical mechanism underlying gamete release. Levels of dissolved inorganic carbon such as carbon dioxide and bicarbonate, they hypothesized, might provide a key.

While the sun is shining, plants take up carbon as they carry out photosynthesis. Brawley and her team reasoned that when water is being churned by waves or tidal currents, the plants are constantly receiving new supplies of carbon. Gametes are not released under such circumstances.

That changes, however, when the water is calm. Without turbulence, the carbon supply begins to run out. The UMaine experiments have shown that the carbon deficit is the chemical signal for plants to release their gametes. It is the green light which tells the plants that the water is calm and the time is right for reproduction.

"We did two types of experiments," says Brawley. "One was a series of tests to see what was involved with dissolved inorganic carbon." In those tests, the researchers varied the levels of carbon in the water. They also agitated the water to simulate turbulent conditions. In reach case, the results were consistent with the team's predictions.

"It is a boundary layer disturbance. That's important to show. Many cells have a mechanical response to pushing, bending, something like that, but this is chemical sensing," Brawley says.

"What I expect is that external fertilization is going to be found to be very successful in these organisms. The caveat is that we always have to remember that we're looking at a snapshot of evolution and that not every species is at its heyday. It may be a species that is o
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Contact: Nick Houtman
nick.houtman@umaine.edu
207-581-3777
University of Maine
17-Feb-1998