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Ngoc Nguyen
Michigan State University

Subject Listing - Chemistry
Advisor: Dr. Barbara Sears

Friday, Oral Session 4, Presentation 4, Karpen Hall 035

THE SPECTRUM OF CHLOROPLAST DNA MUTATION CHANGES WHEN CELLS ARE GROWN IN LOW LIGHT

This study tested the hypothesis that oxygen radicals produced by photosynthesis contribute significantly to mutations that occur spontaneously in chloroplast DNA. The type and frequency of spectinomycin resistant mutants of Chlamydomonas reinhardtii that arise in a low light regime were compared to previously characterized mutations when cells were grown in constant high light. Amplification of the DNA region of interest by the polymerase chain reaction (PCR) followed by DNA sequencing enabled the characterization of mutations that occur in the 16S rRNA gene. A novel base substitution and a recurring 12-bp deletion were observed. The overall mutation frequencies were similar under the two growth regimes, although the types of base substitutions were different. Under low light, fewer transversion mutations arose, suggesting that the chloroplast repair system is able to eliminate most of the DNA damage caused by reactive oxygen. Under high light and continuous photosynthetic activity, the oxygen radical byproducts of photosynthesis may overwhelm the repair system.

Advisor: Dr. Barbara Sears, Professor, Department of Plant Biology, Michigan State University, East Lansing, MI