Plant genome size measurement with DNA image cytometry

To test the reliability of DNA image cytometry for the measurement of nucle ar DNA content in plant material, we conducted independent experiments in t wo laboratories using different image analysis instruments for densitometri c measurement of nuclear DNA amount in Feulgen-stained squash preparations of root tips. The 2C nuclear DNA content of the nine species studied spanne d a 100-fold range (approx. 0.3-33 pg). The estimates of nuclear DNA conten t measured with image cytometry methods were comparable to values obtained previously using both photometric cytometry and how cytometry. Image cytome try methods showed little variation among repealed experiments within each laboratory or among different operators using the same instrument. Furtherm ore, the interphase-peak method (measurement of several hundred interphase nuclei per slide) was comparable to the classical prophase/telophase approa ch (measurement of ten early prophase and ten late telophase nuclei per sli de). Hence, DNA image cytometry gives accurate and reproducible results and may be used as an alternative to photometric cytometry in plant nuclear DN A content measurements. In the present study, we propose that two standards for quality control of nuclear DNA content measurement are used in plant D NA image cytometry: (1) the coefficient of variation of the peak should be lower than 6%, and (2) the 4C/2C ratio should be between 1.9 and 2.1. (C) 2 001 Annals of Botany Company.