Cytomixis and a Trisomic in Nigella sativa L.

抄録

Occurrence of cytomixis was detected in the M₂ generation of a lax branching type mutant of Nigella sativa L. obtained through EMS treatment. Presence of cytomixis was restricted only in the prophase I cells of meiotic division. Transfer of nuclear materials from one PMC to the adjacent PMCs took place through cytoplasmic links and it occurred at random and in specific direction within the PMCs. Cytomixis resulted in the formation of aneuploid and polyploid PMCs. Hypo- and hyperploid meiocytes were observed in 19.87% cells. Multivalents were completely absent in the mutant plant which indicated that migration phenomenon has initiated after chromosome pairing in this material. Pollen sterility recorded in the mutant plant was 6.74%. Normal seed setting was not affected in the lax branching mutant.
Aneuploids were detected among 0.65% individuals of the M₃ population following selfing of the mutant, one of which was a trisomic. Phenotypically the trisomic plant was weak with slender stem and drooping lamina. The extra chromosome in the trisomic plant was present mostly as a univalent and rarely as trivalent. The plant was completely seed sterile due to unbalanced condition of the chromosomes in the zygote. The trisomic has arisen possibly as a chance occurrence through union of normal and aneuploid gametes, the latter being the consequences of cytomixis.