Chromosome Bearing rDNA Loci Involved in Meiotic Chromosome Abnormalities

SCARPÍN JONATAN; CHALUP LAURA; GERMAN ROBLEDO; SOLIS NEFFA VIVIANA; SEIJO GUILLERMO

Conferencia; 21st InternationalChromosomes Conference; 2016

Lathyrus macrostachys (2n = 14) is a South American endemicspecies. An initial screening of some populations of this speciesshowed many chromosome irregularities during meiosis in spiteof the reported high stability of its karyotype. Chromosomes locatedoutside of the metaphase plate, bridges and multiple spindlesare among the most frequent irregularities observed that led to theformation of aneuploid microspores. On this basis, a populationstudy of the meiotic behavior was conducted and FISH with 45Sand 5S rDNA was used in pollen mother cells (PMC) in order toshed light on the mechanisms that cause the irregularities and thechromosomes involved in aberrant meiotic behavior. The studywas conducted in 3 populations from NE Argentina. The resultsobtained here revealed that those chromosomes bearing either 45Sor 5S rDNA loci were involved in the chromosome abnormalitiesobserved in higher frequency than expected by chance. The 45SrDNA loci were mainly involved in the formation of bridges, whilethe 5S rDNA loci were associated to the chromosomes located outsideof the metaphase plate, in first and second divisions. Thesechromosomes were further correlated with the occurrence of multiplespindles in the second division. Silver staining revealed thatall additional microcells observed in tetrad stage and 88.19% ofmicro pollen grains had nucleoli. All the data confirm that thechromosomes with rDNA loci are involved in the generation ofaneuploid pollen grains. The association between the meioticbridges and SAT chromosomes may be related to the fact that inmany instances the fibrillar center of nucleoli is formed by therDNA genes of 4 chromatids that may remain entangled as the firstdivision progresses, giving rise to bridges. However, to explain therelationship between the chromosomes bearing the 5S rDNA lociand the observed chromosomes located outside of the metaphaseplate, more research is needed.