MEIOTIC BEHAVIOR OF EXTRA HETEROCHROMATIN IN THE TOMATO: EFFECTS ON SEVERAL VITAL PROCESSES

Abstract

The cytological behavior during meiosis of extra constitutive heterochromatin and the effects of such additions to the tomato genome were investigated. The main source of extra heterochromatin was 2S∙2S, a completely heterochromatic isochromosome carrying a nucleolar organizer in each of its arms. Meiotic behavior of a half-heterochromatic, tertiary chromosome 5L∙2S in the presence of 2S∙2S was studied. Wehn 2S∙2S chromosomes were present in more than two doses, achiasmatic simultaneous pairing of three, four and five arms of these chromosomes was observed. "Ectopic" pairing of 2S∙2S with heterochromatin of nonhomologous chromosomes was also observed. It is postulated that "ectopic" pairing neutralized in part the high percentage of anaphase I equational division of the 2S∙2S chromosomes. In some individuals the 2S∙2S chromosome was found organizing an extra, smaller-than-normal nucleolus during meiotic prophase. Conspicuous nucleolar vacuoles were also observed in the progenies of plants carrying 2S∙2S extra chromosomes. It was found that the 2S∙2S chromosome alters diakinesis association and segregation of the 5L∙7S chromosome when both are in the same cell. 2S∙2S chromosomes reduced chiasma frequency, which was also accompanied by reduction of crossing-over for some of the tested gene intervals when 2S∙2S was present in one dose. No effects of 2S∙2S on chromosome pairing of interspecific hybrids were detected. Another effect produced by the addition of 2S∙2S chromosomes was expressed as leaf necrosis in some individuals.