Nuclear cytology of callus induction and developmentin vitro

Summary

Expiants of immature cotyledons (2 cm in length) ofVicia Raba (2 n=12) were grownin vitro onMitchell andGildow's (1975) medium supplemented with auxin (either IAA or 2,4-D) alone or auxin and kinetin in many possible combinations of concentrations.

Callus induction and development from the immatureVicia faba cotyledons, which contain diploid and endoreduplicated nuclei, followed the following sequence of nuclear events:

• i) resumption of DNA synthesis in both diploid and endoreduplicated nuclei;

• ii) furrowing (lobation) of nuclei which eventually resulted in the formation of binucleate or multinucleate cells, part of which underwent cellularization later on;

• iii) occurrence, between 10 and 25 days of culture, of rare mitoses (mitotic index not exceeding 0.5%) in both intact nuclei (euploid) and nuclear fragments (very wide range of aneuploid chromosome numbers);

• iv) after transfer to fresh medium of the primary calli, increase of the mitotic index to about 5% with rather rapid selection of dividing nuclei in favor of euploid chromosome numbers.

The results are discussed in comparison with other examples of nuclear fragmentation accompanied by mitosis in plant tissue cultures and in relation to the possibility of regenerating aneuploids from such cultures.