Concluding Remarks

The study of Nicotiana ct-DNA reveals that it exhibits a high degree of variability in the restriction fragmet patterns.These patterns are species specific and therefore it can be used as a genetic marker.This offers unique opportunity to study the evolution of organelles.The understanding of the mechanism of molecular evolution of Nicotiana chloroplast genome will also provide a clear clue of the origin of chloroplasts.Our current work on the cloning and sequencing of the genes of the LS of RuBPCase and others from various Nicotiana species has firmly established a strong basis toward reaching this goal.

We thank Mrs.Merkle-Lehman for her assistance in preparing this manuscript.This investigation was supported by NIH grant CM22746-01 and U.S.Dept.of Agriculture cooperative agreement 58-3204-0-157 from the tobacco laboratory.(https://www.daowen.com)