Associations between Growth Rate, Mitotic Frequency, and Chromosome Number in a Plant Tissue Culture^*

Twelve subcultures derived from one explant of normal, white spruce tissue, and 40 subcultures derived from one explant of tumorous, white spruce tissue, were studied over seven successive transfers. The tumor subcultures showed greater variation than the normal subcultures with respect to chromosome number, rate of cell division, and rate of growth.

In both tissues, by far the greater variance in growth rate was found between subcultures rather than within subcultures over successive transfers. The intra-class correlation was +.93 for the tumor subcultures and +.67 for the normal subcultures, both significant at the .001 level. These correlations indicate that the subculture variation in growth rate is mostly of a genetic nature.

Significant correlations were found among growth rate, rate of cell division, and chromosome number in both the tumor and normal subcultures. The most important finding is the association between chromosome number and growth rate over the entire aneuploid series. As a plausible hypothesis to explain these associations the authors suggest that there is a cause-and-effect relationship from chromosome number through rate of cell division to growth rate.