Synaptonemal complex transformations in rye microsporocytes at the diplotene stage of meiosis

Abstract

The process of synaptonemal complex degradation during diplotene was studied in spreads of rye microsporocytes stained with silver nitrate at pH 3.5–4.5 and 6.0–8.0. Two different patterns of the synaptonemal complex degradation process have been observed, depending on the two staining procedures used. Progressive synaptonemal complex fragmentation observable at the higher pH appeared to be absent in staining at pH 3.5–4.5: thin connecting threads have been found in the "gaps" between the synaptonemal complex segments. Complete tracing of the synaptonemal complex degradation process was attempted and revealed the following successive steps: (i) local repulsion of lateral elements; (ii) lateral element looping in the regions of repulsion; (iii) extension of the loops; (iv) transformation of the extended loops into coils of irregular shape with a diameter of about 2 μm and a pitch of about 1.2 μm; and (v) formation of paired beanlike thickenings on a gyral coil. In asynaptic mutant sy-9 unpaired lateral elements are transformed without looping into a similar coil but with single beanlike thickenings. We conclude that synaptonemal complex lateral element loops at diplotene are invisible after the routine silver staining of microspreads (at pH about 6 and higher) and look like gaps between discontinuous synaptonemal complex segments, thus simulating the process of synaptonemal complex fragmentation.Key words: synaptonemal complex, diplotene, rye.