Enzymes Give Plants UV Protection
Sunlight would kill plants, without enzyme "scissors" that undo
gene damage from ultraviolet (UV) rays. In fact, plants have several natural
gene menders tailored to the kind of damage done, according to findings of an
Agricultural Research Service scientist
working with a researcher at the University of California at Davis.
Ultraviolet damage to crops is rare. But knowing the repair mechanisms may
be important if UV radiation increases in the future as a result of thinning of
Earth's protective ozone layer.
The scientists used Arabidopsis, a common white-flowered plant with a
small number of genes, which allows for easy tracking of genetic differences.
DNA is a series of chemical bases--A-G-C-T (for adenine, guanine, cystosine,
and thiamine)--that form the alphabet of life. If they get damaged, the code is
illegible; too much unreadable code and the plant dies.
Plants may respond in several ways to gene damage.
"When your car breaks down, says ARS plant physiologist Edwin L.
Fiscus, "you can call someone who does general repairs. But other times, a
specialist may be able to perform a particular type of repair much more rapidly
"It's like that for plant cell damage," says Fiscus, who works in
the ARS Air Quality-Plant Growth and Development Research Unit. "To fix
damaged DNA, there are both general repair enzymes and at least two highly
Fiscus and geneticist Anne Britt at UC-Davis confirmed what others
suspected: that two specialized enzymes in plants are essential for UV repair.
They are both from a class of enzymes called photolyases.
The generalized repair enzyme system, says Britt, is probably designed for a
wide variety of relatively rare types of damage. It works by excising the
damaged bases, or sequences, and rebuilding them--a process that tends to be
slow and inefficient.
More common kinds of damage, such as when UV light causes Ts and Cs to
crosslink improperly to each other, are also repaired by specialized
photolyases, which eliminate this inappropriate bond between the bases.
Photolyase repair is specific, rapid, efficient, and--like excision
Another interesting thing about these enzymes, Britt says, is that they are
activated by light, so the very cause of the UV damage is also what triggers
The scientists proved photolyase enzymes are essential for plants' survival
in natural light by using special mutant plants developed by Britt that can't
produce the enzymes.
Fiscus, whose research station is on the campus of North Carolina State
University, devised special growth chambers that delivered precise doses of
various ratios of UV light and regular sunlight. The mutant plants were highly
sensitive to UV light, compared to normal plants.--By
Jill Lee, Agricultural Research
Service Information Staff.
Edwin L. Fiscus is in the
Quality-Plant Growth and Development Research Unit, 1509 Varsity Dr.,
Raleigh, NC 27606; phone (919) 515-3505, fax (919) 515-5044.
"Enzymes Give Plants UV Protection" was published in the
October 1998 issue of Agricultural Research magazine. Click here to see this
issue's table of contents.