BAR-LIKE AND THORN-LIKE ABNORMALITIES IN SYNAPTONEMAL COMPLEXES OF A MUTANT RYE, SECALE-CEREALE

A novel type of aberration in synaptonemal complex (SC) assembly was f ound in electron micrographs of surface spread midprophase I nuclei fr om pollen mother cell preparations of rye. The plants with the mutant phenotype were selected from the fifth- to seventh-generation progenie s of an inbred line (Ms6) characterised by partially reduced fertility and known to segregate for the desynaptic mutation sy6. The SC abnorm ality designated mei6 was at first detected in three sibling plants of the fifth generation of the inbred line. The most striking features w ere (i) the thorn-like protrusions of the lateral elements (LEs), whic h were often folded over towards the opposite LE, and (ii) peculiar ba rs inside the central region of the SC, which were either obliquely or perpendicularly positioned between the LEs. The bars and thorns often coincide with discontinuities in the adjacent LEs, giving rise, in a few cases, to minor branched structures. We analysed 424 surface sprea d pachytene nuclei obtained from 26 plants selected from the three inb red generations. Bars represented 92% of all abnormalities: their numb er per cell increased significantly with the progress of meiotic proph ase, varying from an average of 1.96 +/- 0.39 at midzygotene to 5.16 /- 0.52 at late pachytene and 5.14 +/- 0.91 at early diplotene. Our ob servations suggest that bars are caused by modification and (or) erron eous self-assembly of meiosis-specific proteins intercalating with LE proteins at or near the sites of crossover events. It is also probable that the gene(s) involved is inherited independently from the gene fo r desynapsis.