M. 1981. Cytophotometric study and statistical analysis of ploidy evolution in cultured tissues oi Nicotiana tabacum. -Physiol. Plant. 51: 207-214.Evolution of the ploidy in four strains oi Nicotiana tabacum cv. P 19 was studied by cytophotometry after transformation of the cultured tissues into protoplast suspensions. The limits of these variations were analysed numerically and statistically. The method used is capable of wide application. It can be used to predict the evolution of the average ploidy level of a strain maintained on a given medium if the average ploidy level of the explant is known. Comparison is made relative to a standard of known ploidy (diploid protoplasts). Increase of the average ploidy level is faster when the explant is mainly diploid (leaf parenchyma) than when it is composed of more heterogeneous tissues as regards ploidy (shoot tip). The appearance of a random drift depends on the composition of the culture medium; it is immediate in one medium (MS2), but is preceded by a phase of relative stability in another medium (MS,) which is richer in kinetin. While the results presented specifically concern the strains cultured on media MS, and MS,, the statistical method employed is applicable to cultures of any species for which one can experimentally justify a linear regression analysis.
The ploidy level variations of protoplast cultures of Nicotiana plumbaginifolta Viviani (n = 10) were investigated from protoplast isolation until regenerated buds, using cytophotometric measurements of nuclear DNA content and chromosome counting. An increase in the average nuclear DNA amount has been found to occur in freshly isolated protoplasts after 15 hours of maceration. Cytological abnormalities like nuclear fragmentation, chromatin connections between interphasic nuclei and micronuclei were observed during the following days. Chromosome counting in 15, 30 and 50-day-old calli and in regenerated buds revealed that nuclei are haploid, diploid or aneuploid.
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