The DNA C value is an important biological characteristic and the knowledge of DNA content may be applied to several branches of science. Nuclear DNA content determinations, normally performed by Feulgen microdensitometry and flow cytometry, may replace chromosome counts especially when a high number of individuals are being analysed. Feulgen microdensitometry is based on the affinity of this dye and the DNA: the amount of DNA is proportional to the amount of dye taken by the nucleus. Flow cytometry is based on the optical properties of particles on a flow. In plants the technique basically consists in the isolation of nuclei, staining with a fluorochrome and measurement of the emitted fluorescence. The advantages of this technique, when compared to Feulgen densitometry, are the relative easiness and speed of sample preparation, the possibility to analyse a high number of nuclei, the need of small tissue amounts and the detection of small differences in DNA contents. Conflicting results from different authors show the need of a rigid technical standardization so that methodological errors are not misinterpreted with eventual real differences in DNA contents.
nuclear DNA content; Feulgen; flow cytometry