Introduction

In higher plants，chloroplasc DNA（ct-DNA）was traditionally considered to be highly conserved.This concept arose from the observation that ct-DNA exists in multiple copies per organelle（Herrmann，1970；Kirk，1971）.The strong conservative force of ct-DNA polyploidy in evolution was supported by the homologous coding information for rRNA，tRNA，and the large subunit of ribulose 1，5-bisphosphate carboxylase（RuBPCase）as well as the remarkably uniform physicochemical properties of higher plant ct-DNA（Kung，1977；Bedbrook and Kolodner，1979）.Recently，however，studies of ct-DNA by restriction enzyme（Atchison et al.，1976；Vedel et al.，1976；Frankel et at.，1979）and DNA hybridization techniques（Bisaro and Siegel，1980）have demonstrated a diversity among chloroplast genomes which was more pronounced as the taxonomic plant groups diverged.Thus ct-DNA restriction patterns of closely related plants would be expected to have many fragment size classes in common.While this was not the case with ct-DNA from Cucumis or Lupinus species（Atchison et al.，1976），striking similarities in restriction fragment patterns haive been observed with ct-DNA from several wheat（Vedel and Quetier，1978）and Nicotiana（Atchison et al.，1976）species.

P.R.Rhodes，Y.S.Zhu，and S.D.Kung，Department of Biological Sciences.University of Maryland.Baltimore County（UMBC），Catonsville.MD 21228.USA

此文发表于“Mol.Gel.Genet”182：106-111.(https://www.daowen.com)

Variations in ct-DNA nucleotide sequence among Nicotiana species have been demonstrated for the highly conserved large subunit of RuBPCase（Kung et al.，1977）.As we report here，these differences in the primary structure of RuBPCase large subunit can be correlated with the ct-DNA restriction pattern.Furthermore.variation in the ct-DNA restriction pattern parallel the accumulated geographic.morphological.and cytogenetic evidence upon which the taxonomic classification of Nicotiana species is based.