Plants and Magnetic Field
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It's common knowledge that some animals can detect and use Earth's magnetic field, but now Italian researchers have identified a possible mechanism by which plants might react to it as well.

The researchers even ponder the possibility that surges of plant evolution in Earth's history -- especially the appearance and spread of flowering plants -- might match times when the Earth's flip-flopping magnetic poles were like that of today.

"Compared to studies in animals, very little is known about magneto-reception in plants, although early studies on plants were initiated more than 70 years ago," explains the University of Turin's Andrea Occhipinti and colleagues in a paper in the January issue of the journal Trends in Plant Science.

There have been studies that suggest that plants do, indeed, respond to both strong and weak magnetic fields, but the experiments have been hard to duplicate, leaving a lot of questions still unanswered, the researchers wrote.

In birds the trick to detecting magnetic fields is the existence of a blue-light receptor protein, called a cryptochrome, in the birds' eyes. Cryptochromes are thought to be activated by light, and then they become sensitive to a magnetic field.

Oddly enough, the same protein has been found in plants, where, theoretically, they might also enable plants to react to magnetic fields. The big question, of course, is what use would a plant have for this extra ability? After all, plants don't migrate.

"Plants probably don't sense the Earth's magnetic field," said physicist Ilia A. Solov'yov of the University of Southern Denmark. Solov'yov has done work on cryptochromes, which are actually very common and exist in humans as well, he said.

"The fact that they have cryptochromes is probably an artifact in the same way that people have them," Solov'yov said, without the ability to use them to navigate. Evolution leaves relics behind -- think of your appendix, little toe or wisdom teeth - which sometimes find new uses, gradually disappear, or mysteriously stick around.

One possible function in plants, suggests Occhipinti, could be to help plants react to elements in soils that are affected by magnetic fields, like some forms of calcium. For now, there are more questions than answers, according to Occhipinti.

"Why should plants regulate their physiological processes in response to variation of (the global magnetic field)? How does (the magnetic field) affect plant development, and do cryptochrome-related biophysical mechanisms play a role in plant magnetoreception?" Occhipinti asks.

And what about changes in the Earth's magnetic field? Do they have anything to do with plant evolution?

"Some authors have pointed out that, during geomagnetic reversals, (life) is exposed to more intense cosmic radiation and/or UV light," Occhipinti said. That could theoretically cause more damage to genetic material, which causes more mutations which, in turn, could speed up the rate at which new species cold evolve.

Occhipinti's team looked at the Earth's magnetic history and reported what they say is just such a pattern in flowering plants (angiosperms) which first came into being about 136 million years ago.

They found that during periods when Earth's magnetic field was like today (when the compass points north instead of south) there appear to have been more new families of angiosperms evolving than during reversed magnetic fields.

"This correlation appears to be particularly relevant for angiosperms compared to other plants," Occhipinti points out. Of course, other factors could explain this, such as global climate changes, or the rise of grasses as the dominant plants, which has been linked to global cooling and drying.

The bottom line, says Occhipinti, is that Earth's magnetic field and magneto-reception might be a relevant factor in plant evolution -- so it's worth investigating.