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Vitamin C Protects Stressed-Out Plants

By Rosalie Marion Bliss
January 21, 2003

People aren't the only ones using antioxidants to protect their cells. Plants also use the antioxidant vitamin C--which they produce themselves--to reduce oxidative cell damage. Agricultural Research Service scientists are looking into ways that plants use vitamin C to defend against ozone, which damages more plants than all other air pollutants combined.

Stratospheric, or upper-level, ozone protects Earth from damaging, ultraviolet radiation. But tropospheric, or ground-level, ozone, is a pollutant. Tropospheric ozone enters plants through their leaves and decomposes into unstable molecules called reactive oxygen intermediates (ROIs). If not neutralized by an antioxidant, ROIs injure plants.

At the ARS Air Quality-Plant Growth and Development Research Unit in Raleigh, N.C., plant physiologist Kent Burkey is studying how plants transport vitamin C out of their leaf cells and into a complex of adjoining cell walls. This outer cellular space, called the apoplast, is an interconnected liquid layer surrounding the cells.

Burkey has found that plants that are able to move greater quantities of vitamin C into the leaf apoplast have a better chance of detoxifying ozone.

He has evidence that ozone tolerance in snap beans is associated with elevated vitamin C in the leaf apoplast. He also has found that plants vary widely in terms of how much vitamin C they make inside their cells. But while some plants make lots of vitamin C in their cells, they are not capable of pumping it into the apoplast where it can provide protection against ozone injury.

Burkey's most recent tests on snap beans suggest that the presence of vitamin C in the apoplast before ozone enters the leaf is critical.

He will next look more closely at how vitamin C and derivatives are pumped between the cell and the apoplast. And he will be looking for other antioxidant compounds in the leaf apoplast that could protect against ozone injury.

Read more on this in the January issue of Agricultural Research magazine.

ARS is the chief scientific research agency of the U.S. Department of Agriculture.