 of enzyme molecules in each rice cell. By varying the time before giving the single flash, the researchers can measure how the enzyme functions over time.
If there is a normal amount of normal enzyme, an early flash will yield a small number of repairs. Waiting longer before giving the flash -- so that more enzyme molecules can bind to damaged sites -- will yield higher numbers of repairs until, at a certain time, all the damaged sites are fixed with one flash.
If there is too little enzyme, however, no matter how long the scientists wait to give the flash, some damage sites would remain unrepaired. If, instead, the problem is a defective enzyme present in normal amounts, all damaged sites would eventually be fixed, as happens with normal enzymes, but it would take a longer time.
This second situation is what the scientists observed. The Norin 1 enzymes didn't fix many damage sites with an early flash. But if the scientists waited long enough to give the flash (much longer than needed for enzymes from a normal strain of rice), the enzymes were able to bind and fix all the damage.
Since the scientists now suspected that the problem was with the enzyme's ability to bind to the DNA damage sites, and that the faulty enzyme-DNA complexes might be more susceptible to heat, they tested this hypothesis with a second experiment. They showed that the enzyme from Norin 1 disassociates from DNA more readily when exposed to heat than repair enzymes from a non-UV-sensitive rice strain.
These findings indicate that the problem is in the structure/functioning of the enzyme. Sutherland suggests this defect could be fixed by cross-breeding Norin 1 with strains that carry the gene for the correctly functioning enzyme. Alternatively, scientists might be able to introduce the correct gene into the Norin 1 strain.
"These approaches to improving the ability of plants to repair UV-induced damage could allow significant increases in productivity of this and other economically important crop plants," Sutherland says.
This research was funded by the Japanese Ministry of Education, Culture, and Science; the 2nd Toyota High-tech Research Grant Program; and the Office of Biological and Environmental Research of the U.S. Department of Energy.
The U.S. Department of Energy's Brookhaven National Laboratory creates and operates major facilities available to university, industrial and government personnel for basic and applied research in the physical, biomedical and environmental sciences and in selected energy technologies. The Laboratory is operated by Brookhaven Science Associates, a not-for-profit research management company, under contract with the U.S. Department of Energy.
The above story is based on materials provided by Brookhaven National Laboratory. Note: Materials may be edited for content and length.
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