Inside Science News Briefs

A collection of brief stories from the world of science

By Jim Dawson
Inside Science News Service
November 10, 2008

Annuals versus Perennials -- Not a Garden Variety Solution

Scientists with the Flanders Institute for Biotechnology in Gent, Belgium, have determined what makes plants either "annual," meaning they live one growing season and die, or "perennial," meaning they regrow every spring. The difference, according to work done by scientist Siegbert Melzer, comes down to two critical flower-inducing genes that, when turned off, can turn an annual into a perennial. The rapid growth of flowers, and then seeds, is the strategy most annuals use to propagate from one generation to the next and one growing season to the next. Annuals experience "rapid growth following germination and rapid transition to flower and seed formation, thus preventing the loss of energy needed to create permanent structures," said a statement about the research from the institute. "They germinate quickly after the winter so that they come out before other plants, thus eliminating the need to compete for food and light. The trick is basically to make as many seeds as possible in as short a time as possible."

Perennials instead build "structures" such as overwintering buds, bulbs or tubers, that contain cells that are not yet specialized and, when the next growing season begins, can be converted into stalks and leaves. An annual uses up all of its non-specialized cells making flowers, and thus, after dropping seeds, it dies. The growth of the flowers is triggered by the plant sensing the length of day and amount of sunlight. When the light is just right, "blooming-induction genes" are triggered. By deactivating two of the genes that induce flower growth in the thale cress, a flowering plant whose genome has been entirely sequenced, the researchers created mutant plants that "can no longer induce flowering, but . . . can continue to grow vegetatively or come into flower much later." Because the plants don't use up the store of non-specialized cells making flowers, they become perennials, able to continue to grow for a long time. And, like true perennials, the altered annuals show secondary growth with wood formation.

Why do Heart Attacks and Strokes Peak in the Morning?

Heart attacks and strokes most often occur in the morning, just as a person's biological clocks are turning on many physical systems in preparation for the day's activities. Scientists have long been aware of the link between biological rhythms and heart attacks, but now researchers from the Emory University School of Medicine have found that the daily rhythms of cells that line blood vessels may be part of the reason. Endothelial cells in blood vessels serve as the interface between the blood and the arteries, controlling arterial tone and helping to prevent clots that lead to heart attacks and strokes, a release from the medical school said. These cells, which help blood vessels relax, are created from progenitor cells that come from the bone marrow.

In the study, Ibhar Al Mheid, an MD and cardiology researcher, measured blood samples taken from a dozen healthy, middle-aged subjects every four hours for 24 hours. They found that the ability of blood vessels to relax and the ability of progenitor cells to grow peaked at midnight, about four hours after the peak in the number of endothelial cells. "The lining of our [blood] vessels appears to function better at night than in the day," Al Mheid said. "Endothelial function is particularly depressed in early morning hours."

Past studies of the biological rhythm of the human heart, done by other researchers, show that various factors regulate the efficiency of the heart itself, and that typically it is most able to tolerate stress around 5 p.m., and least able to handle it around 9 a.m.

Maybe the Dinosaurs Didn't Dance

A report in mid-October by University of Utah geologists that they had found a "dinosaur dance floor" - a wilderness area containing at least a thousand dinosaur footprints - has been called into question by a group of paleontologists who visited the site. A week after the "dance floor" received world-wide media attention, four paleontologists from other institutions hiked to the remote area within the Vermillion Cliffs National Monument on the Arizona-Utah border. They reported they saw dinosaur track marks while hiking to the site, but none on the pockmarked dance floor itself.

"There simply are no tracks or real track-like features at this site," said Brent Breithaupt, director of the University of Wyoming's Geological museum. The depressions that the University of Utah geologists interpreted as fossil footprints are more likely potholes, the team of paleontologists said. Marjorie Chan, chair of geology and geophysics at Utah, was a co-author on the paper that described the depressions as likely dinosaur footprints. In reaction to the comments from the paleontologists, she said if the features are potholes, they are extremely unusual compared with typical potholes in the region.

Chan and Winston Seiler, who conducted the research as part of his master's thesis, said they were not retracting their study, which was published in Palaios, an international paleontology journal. But they acknowledged that there are arguments for the features being potholes instead of dinosaur tracks, and noted that they said that was a possibility in their paper. "Science is an evolving process where we seek the truth," Chan said. "We went through the proper scientific process of careful study, comparisons with other published works, and peer review. We gave the project considerable critical though and came up with a different interpretation than the paleontologists, but we are open to dialogue and look forward to collaborating to resolve the controversy."

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