bendich@u.washington.edu
522 Hitchcock
http://www.biology.washington.edu/index.html?navID=42&parecID=12
The chromosome is the segregating genetic unit. We study the structure and replication of intact chromosomal DNA from chloroplasts and mitochondria of plants. After gentle lysis, electrophorectic movement of the DNA molecule is recorded in real-time moving pictures using fluorescence microscopy.
Most of the DNA is found in linear and complex, branched molecules larger than the size of the genome, and not in the circular molecules predicted by DNA fragment mapping. These large molecules, rather than the predicted circles, probably represent both the replicating and inherited forms (the chromosomes) of organellar DNA.
We find that the amount of DNA per chloroplast decreases as plastids green, expand, and mature in the expanding cells of the leaf. The molecular integrity of the DNA also diminishes during chloroplast development. This degradation of chloroplast DNA is rapid in maize and gradual in tobacco. We are currently studying the mechanism of loss or retention of organellar DNA and ways to improve genetic transformation of chloroplasts.
