Chromosome pairing in meiosis usually starts in the vicinity of the telomere attachment to the nuclear membrane and congregation of telomeres in the leptotene bouquet is believed responsible for bringing homologue pairs together. In a heterozygote for an inversion of a rye (Secale cereale L.) chromosome arm in wheat, a distal segment of the normal homologue is capable of chiasmate pairing with its counterpart in the inverted arm, located near the centromere. Using 3D imaging confocal microscopy, we observed that some telomeres failed to be incorporated into the bouquet and occupied various positions throughout the entire volume of the nucleus, including the centromere pole. Rye telomeres appeared ca. 21 times more likely to fail to be included in the telomere bouquet than wheat telomeres. The frequency of the out-of-bouquet rye telomere position in leptotene was virtually identical to the frequency of telomeres deviating from Rabl's orientation in the nuclei of somatic cells, and was similar to the frequency of synapsis of the normal and inverted chromosome arms, but lower than the MI pairing frequency of segments of these two arms normally positioned across the volume of the nucleus. Out-of-position placement of the rye telomeres may be responsible for reduced MI pairing of rye chromosomes in hybrids with wheat and their disproportionate contribution to aneuploidy, but appears responsible for initiating chiasmate pairing of distantly positioned segments of homology in an inversion heterozygote.

Centre for Agricultural Research Agricultural Institute Hungarian Academy of Sciences Martonvasar 2462 Hungary National Food Chain Safety Office Budaörsi Str 141 145 Budapest 1118 Hungary

Centre of the Region Hana for Biotechnological and Agricultural Research Institute of Experimental Botany Slechtitelu 31 Olomouc Czech Republic

Department of Botany and Plant Sciences University of California Riverside CA 92521 USA

Faculty of Science Centre of the Region Hana for Biotechnological and Agricultural Research Department of Cell Biology Palacky University Olomouc Slechtitelu 27 Olomouc Czech Republic

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