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Revving up an amino acid that plants already contain might protect them from
a host of environmental stresses, such as heat, salt, drought or herbicides,
University of Nebraska-Lincoln research indicates, May 2005 by Vicki Miller.

Plant Pathologist Marty Dickman and colleagues discovered a previously
unrecognized protective power of proline, an amino acid, by chance while
studying what regulates cell death in plants.

Proline is known for protecting plants against drought and salt stress by
helping cells retain water. This research revealed a potentially much
broader protective role for proline as a potent antioxidant that also
inhibits cell death.

So far, the Institute of Agriculture and Natural Resources team has tested
proline in the lab on an alfalfa fungus and a yeast with surprising results.
When researchers added proline to the lab dishes containing the fungus or
yeast, the organisms survived environmental stresses, including heat,
ultraviolet light, salt, hydrogen peroxide and herbicide treatment.

While he's excited by the findings, which were published earlier this year
in the Proceedings of the National Academies of Science, Dickman is
cautious. He points out that what works in a fungus or yeast doesn't
automatically translate to plants or animals.

"Our research suggests the potential value of proline as an antioxidant,"
Dickman said. "We want to be realistic but what we've seen so far suggests
proline has a broader protective function than previously realized. That's
motivation to expand our research into plants and animals."

Dickman's team made the proline discovery while working with a mutant form
of a fungus that attacks alfalfa. The mutant contained a cancer-like gene
that made it grow abnormally under certain conditions. In a nutritionally
rich growth medium, the mutant grew normally but in a nutritionally sparse
medium "it was messed up," he said.

The nutritionally rich growth medium was composed of vitamins and amino
acids. Dickman wanted to know specifically which component restored normal
growth in the mutant fungus. The team ruled out vitamins and a graduate
student then tested 20 amino acids one at a time on the mutant fungus.

"We got lucky. One amino acid, proline, restored normal fungal growth," he
said, "but we had no idea why."

To learn more, the IANR team grew the mutant fungus in the presence of known
antioxidant compounds and then with proline. Antioxidants counteract cell
damage caused by free radicals and other forms of toxic oxygen that damage
cells through oxidation.

Proline had the same effect as the antioxidants. It restored normal growth
and removed virtually all of the toxic oxygen. Scientists also found that
proline prevented programmed cell death, or apotosis. In programmed cell
death, cells essentially commit suicide as part of the cycle of cell
replacement and disease or injury protection. When an organism is being
attacked or stressed, damaged or old cells die to protect healthy cells.

In other experiments the team exposed a normal alfalfa fungus to
life-threatening stressors including heat, salt, hydrogen peroxide or UV
light. Without added proline, the fungus died. When it was added, the
stressed fungus survived and programmed cell death ceased.

"We were pretty excited about this," Dickman said. "Even though this was in
a fungus, we thought that if proline works, it could have a broader role
than previously recognized."

To find out, Dickman tested proline in baker's yeast that had been treated
with paraquat, a herbicide that kills plants by generating destructive toxic
oxygen that kills cells. Results were the same: Yeast grown in the presence
of paraquat died while yeast grown with paraquat and proline grew.

"We can impose various stresses from UV to paraquat and basically, what's
lethal without proline grows just fine with it," Dickman said.

Dickman is beginning tests to determine whether proline has the same
protective power in plants. He's also collaborating with UNL biochemist Don
Becker on research to more specifically understand proline's protective
mechanism.

If proline proves effective in further studies, "we might be able to
generate plants with broad spectrum stress tolerance," Dickman said.

That's appealing because scientists might be able to simply boost the
activity of an amino acid that's already present in plants to enhance their
resistance to stresses. Typically in genetic engineering, scientists must
look for to other organisms for genes with the desirable characteristics.

"A little bit of tweaking and we could have stress protection," Dickman
said.

The National Science Foundation and the university's Redox Biology Center
helped fund this IANR Agricultural Research Division research.

[ianrnews.unl.edu]

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