Search

A 0.1% caffeine solution has been injected into plants of rye at various stages of spike development. Cytokinesis was inhibited in the germ line, and the resulting binucleate cells underwent bimeiosis. Nuclear fusions occurred during cell divisions of the germ line, giving rise to mononucleate tetraploid PMCs which showed 14 bivalents instead of the expected up to 7 quadrivalents. A decrease in chiasma frequency was also noted.

In order to investigate wheter colchicine affects crossing-over, rye anthers of an inbred line of rye forming bridges and fragments at anaphase I produced by erroneous chiasmata, and anthers of plants heterozygous for a conspicuous heterochromatin band, were cultured in a medium with colchicine. Anthers planted at zygotene did not show bridges at AI in the inbred line. In the heterozygotes no difference between associated chromatids in respect to the heterochromatin band, resulting from crossingover, were observed. In anthers planted at pachytene both bridges and chromosomes showing difference between associated chromatids were observed at a stage equivalent to AI with the same frequency as in anaphase I cells of untreated anthers. This demonstrates that crossing-over or a prerequisite to crossing-over is established at zygotene, and also that absence of chiasmate association at later stages is not due to precocious slipping off of chiasmata.

Rye anthers were cultured in medium with colchicine for periods of 12–24 h. Unaffected PMCs showed normal meiotic pairing in the same anthers in which other PMCs showed several degrees of asynapsis (or desynapsis), c-meiosis or anaphase irregularities. Pairing was affected only in cells which were at mid zygotene at the time of treatment initiation. Chiasma terminalization and release was possible in the absence of a functional spindle. Possibly, spindle function is more sensitive to colchicine than pairing. Variation within anthers can be adscribed to gradients in stage and development. The possibility of differences in penetration of colchicine must be recognized.