The isolation of apparently homoplastidic mutants induced by a nuclear recessive gene in Arabidopsis thaliana.

The nuclear recessive gene, chm1, of Arabidopsis thaliana is a imitator that induces a variety of plastid alterations giving rise to mixed cells and variegated leaves. The variegation is maternally transmitted but chm1 is transmitted in a Mendelian fashion (Rédei 1973; Rédei and Plurad 1973). In order to characterize the different types of plastid alterations induced by chm1, isolating homoplastidic lines, each apparently containing one type of mutant plastid in its cells, was essential since such characterization cannot be carried out on mixed cells. We have used two genetic approaches to isolate several apparently homoplastidic mutant lines by the removal of the mutator from the genetic background, and the maternal transmission of the mutant plastids. The rapidity of obtaining homoplastidic lines in the absence of chm1 indicated a non-stochastic sorting-out of plastids in mixed cells. That each of the chm1-free homoplastidic mutant lines was apparently homoplastidic for one type of mutant plastids was confirmed by electron microscopic observations. Here we report, for the first time, the production of different homoplastidic lines in the absence of the nuclear-mutator gene. Such genetically-stable homogeneous material should be a useful tool for studying the molecular mechanism(s) by which chm1 induces a variety of heritable plastid alterations.