A mutation causing variegation and abnormal development in tobacco is associated with an altered mitochondrial DNA

Abstract

A variegated mutation appeared in the leaves of a tobacco cybrid plant resulting from fusion of protoplasts from tobacco with Petunia. The mutation was inherited maternally. The light green coloration of leaf sectors resulted from a substitution of spongy parenchyma for palisade parenchyma. No defects were detected in the chloroplasts of the plants, which were derived from Petunia. The mitochondria, as judged by the electrophoretic pattern of their DNA after digestion with restriction endonucleases, were very similar to mitochondria of tobacco, although with some unique cybrid-specific fragments. A second round of fusions was performed to confirm that mitochondria, rather than chloroplasts, were associated with the variegated phenotype. In these fusions, the Petunia chloroplasts of the variegated plants were replaced by tobacco chloroplasts. The mitochondria, according to the DNA restriction pattern, retained all or some of the unique cybrid-specific fragments found in the original variegated tobacco cybrid. Since the variegated phenotype remained after the chloroplast exchange, the chloroplast DNA cannot be the site of the mutation which is responsible for the mutant phenotype. This result eliminates the chloroplast and confirms that the mitochondrial genome is associated with the mutant phenotype.