Cytomixis-like chromosomes/chromatin elimination from pollen mother cells (PMCs) in wheat-rye allopolyploids

Polyploidy is an important event and major force in plant speciation. Amongst the polyploids, allopolyploids have attracted special attention to investigate genetic and epigenetic mechanisms. Also, they are the means for the development of new genotypes and genomic combinations to facilitate genetic enhancement and agricultural productivity. Whereas natural allopolyploids are genetically stable and well adapted, the newly synthesized ones are highly unstable. This instability is manifested into alterations at genomic and/or phenotypic level. Here we present the phenomenon of direct chromosome/chromatin elimination from pollen mother cells (PMCs) in wheat-rye hybrids as one aspect of instability leading to irregular meiosis and disturbances in meiotic process. One of the prominent irregularities noticed is peripherally separated uncondensed or pycnotic masses of chromatin in all meiotic stages. We have observed that this chromatin undergoes elimination by budding-like way, whereby a mini-cell is created. It was also found that nucleoli are the first to be eliminated along with a small mass of chromatin. By means of GISH we have shown that both rye and wheat chromatin might be eliminated. In the separated groups of chromosomes/chromatin neither DNaseI nor DNase II activity was detected. Immunolocalization of tubulin allowed for differentiation between chromatin elimination from microspores and elimination from earlier stages of meiosis. It was noticeable, that in microspores special cytoskeleton structure pushing micronuclei out from the cells was created. Elimination occurred before and after meiosis as well as in each stage of meiotic division, but its intensity varied, depending on the PMC. The basis of the elimination mechanism might be the same as in cytomixis, because both phenomena share common symptoms, although cytomixis per se was rare in the analyzed hybrids.