Effects of elevated temperature on meiotic chromosome synapsis in Allium ursinum

Synaptonemal complex (SC) formation in microsporocytes of Allium ursinum is severely affected by exposure of plants to 35° C for 30 h or longer. In spread preparations made from fresh and freeze-conserved material it was found that a high proportion of meiocytes is arrested at leptotene and shows no synapsis at all. In another group of nuclei synaptonemal polycomplex-like structures do occur between converging axial elements at presumed rudimentary SC initiation sites. Axial elements are virtually always thickened at these sites which seem to involve primarily heterologous chromosomes. A third situation is seen in nuclei where two or more lateral elements are engaged in the formation of longer stretches of aberrant SCs. These feature surplus material filling the central space. It may be assumed that this abnormal condition precludes crossing over and hence may be one of several ways by which elevated temperatures cause the chiasma reduction described here for A. ursinum and reported for several other organisms in the literature.