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UV Light Discovery Surprises Scientists

PULLMAN, Wash. — Ultra violet light triggers plant defense mechanisms.

This surprising discovery by Washington State University scientists was totally unexpected and is the opposite of what scientists had assumed about the ways that ultra violet light influences plants.

It is of such a fundamental nature that Clarence Ryan, a member of the Academy of Sciences, believes it will impact both plants and animals. It could even raise questions about how ultra violet irradiation might affect the relationships between plants and animals in the growing ozone hole in the earth’s atmosphere.

Exposure to higher levels of ultra violet light, which can be injurious, instead may be advantageous to plants, Ryan says.

These findings by a team of four WSU scientists in the Institute of Biological Chemistry and the Department of Biochemistry and Biophysics were reported in the Oct. 31 issue of “Nature,” a prestigious scientific journal published in London. Involved were Ryan, Antonio Conconi, Michael J. Smerdon and Gregg A. Howe.

The research is an outgrowth of Ryan’s career-long work on how plants protect themselves from insect attacks. The scientists were trying to sort out all of the individual biochemical steps involved in the basic message signaling process.

One Sunday morning Conconi, then a post-doctoral assistant to Ryan, proposed an experiment as a secondary project to see what ultra violet light would do to proteinase inhibitor genes. They were especially interested in how it would influence repair of damage to chromosomes.

“It was just kind of a fun thing,” Conconi recalls.

The scientists discovered that ultra violet light activates a series of over 15 defense proteins. “When we saw the result we became very excited about it,” Ryan says. “This is something that no one even suspected.

“The experiments were just so clear and so compelling,” Ryan says, that the team had to pursue it. As evidence mounted, it became obvious that they were studying a mechanism that relates not only to plant life, but to animals.

Now a research scientist in Smerdon’s laboratory in biological physics, Conconi is studying the effects of ultra violet light on DNA repair linked to gene transport in frogs and yeast cells.

The WSU research shows that ultra violet light’s influence is at a very fundamental level on the message pathway.

Ryan says the little-understood pathway is used for many different functions and has significant impacts on plant development, growth and metabolism.

A very similar pathway in animals leads to an important regulator called prostaglandin.

Ryan says there is growing evidence that plants and animals developed from the same ancestral system. This would explain how ultra violet light could have similar influences on both plants and animals.

“No one ever had any concept of what mechanisms were involved when ultraviolet light activated the defense genes that fight off attackers,” Ryan says.

“It clearly gives plants an advantage toward plant-eating insects and pathogens if their defense system is turned on by increasing ultra violet light.”

The research involved exposing leaves of tomato plants to increasing doses of ultra violet light and analyzing their extracts for specific proteinase inhibitors and the nuclear messages that encode them.

Ryan reported that synthesis of proteinase inhibitors responded incrementally to increases in exposure to the ultra violet light.

“The ultra violet treatment appears to mimic wounding,” Ryan reported. “It gives us a new insight into how ultra violet irradiation might have impacts on ecosystems, not only in the present, but in the evolution of these systems over millions of years.”

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