Did You Know Just That Many Cancers Are Linked To A Vitamin Deficiency?
Vitamin
C protects stressed-out plants: Ozone tolerance in snap
beans is associated with elevated vitamin C in the leaf
apoplast
Agricultural Research, Jan, 2003 by Rosalie Marion Bliss
People aren't the only ones in need of antioxidants to neutralize
free radicals. Scientists have long known that plants use
their own vitamin C to reduce oxidative damage. Now, 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 harmful ultraviolet
radiation. But tropospheric, or ground-level, ozone, is
a pollutant. Tropospheric ozone results when air pollutants
react with oxygen in the presence of sunlight to form a
molecule with three highly charged oxygen atoms ([O.sub.3]).
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 Air Quality-Plant Growth and Development Research Unit
in Raleigh, North Carolina, 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 is called the apoplast--an interconnected
liquid layer surrounding the cells. "We've found that
plants that are able to move greater quantifies of vitamin
C into the leaf apoplast have a better chance of detoxifying
ozone," says Burkey.
He
has evidence that ozone tolerance in snap beans is associated
with elevated vitamin C in the leaf apoplast. He has also
found that plants vary widely in terms of how much vitamin
C they make inside their cells. "But that doesn't seem
to be related to how tolerant they are," says Burkey.
While some plants make lots of vitamin C in their cells,
they are not capable of transporting it into the apoplast,
where it could provide protection against ozone injury.
After
vitamin C neutralizes ROIs, the vitamin C itself becomes
oxidized into dehydroascorbic acid (DHA). The plant then
moves the DHA back into the cell where it is reduced, or
revitalized, into vitamin C, which is once again available
for transport back into the apoplast to fight ozone.
Questions
remain about the protective importance of vitamin C stored
in the apoplast before ozone exposure versus vitamin C that
is pumped into the apoplast in response to ozone stress.
But 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
Vitamin C protects stressed-out plants: Ozone tolerance
in snap beans is associated with elevated vitamin C in the
leaf apoplast.
Agricultural Research, Jan, 2003 by Rosalie Marion Bliss
Continued from page 1.
He will next look
more closely at how vitamin C and DHA are transported between
the cell and the apoplast. And he will look for other antioxidant
compounds in the leaf apoplast that could protect against
ozone injury.
Burkey hopes the
research will lead to finding genes associated with a plant's
ability to pump vitamin C into the leaf apoplast. "You
could potentially develop plants with greater ozone tolerance,"
he says. "Once you have the gene, you could express
it in other plants using molecular techniques."
This research is
part of Air Quality (#203) and Global Change (#204), two
ARS National Programs described on the World Wide Web at
http://www.nps.ars.usda.gov.
Kent O. Burkey is
with the USDA-ARS Air Quality-Plant Growth and Development
Research Unit, 3127 Ligon St., Raleigh, NC 27607; phone
(919) 515-1620, fax (919) 856-4598, e-mail koburkey@unity.ncsu.edu.
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