Micro-interferometry of insect polyploid nuclei.

Interference microscopy has enabled investigators to determine the weight of unstained and even living cells and cellular components by precise optical means and has also provided a direct image of structural details with excellent and control lable contrast and high resolution (Mellors 1957). By interference microscopy measurements of dry mass of genetic material in sperm nuclei of the mouse, the rat and the guinea pig and of the different stages of grasshopper spermatogenesis have been reported (Mellors and Hlinka 1955, Watkins 1961). Detection of polyploid nuclei in quantitative cytological analysis has used the number of chromosomes and, when this cannot be established, estimates of the nuclear DNA from cytophotometry and the nucleus size from caryometry. Micro interferometry procedures for determination of dry mass in polyploid somatic nuclei had been only used in the study of neoplasic cells in mouse tumours (Mellors et al. 1955, Mellors 1957) and of isolated diploid and tetraploid nuclei of adult rat liver (Bibbiani et al. 1969) and were considered of high precision, when com parisons were made with cytophotometric data for DNA. Development of polyploidy in silk glands and Malpighian tubes of insects has been demonstrated in terms of DNA content per nucleus and nuclear size. In Hymenoptera the larval Malpighian tubes of Melipona quadrifasciata have poly ploid nuclei during the post-embryonic development; DNA replications stop in the 3rd instar, while the nuclear volumes enlarge until the 4th instal (Mello and Takahashi 1969). DNA contents and nuclear volumes in the silk glands of the same bee increase until the 4th larval instar, but the increase in nuclear volume is greater than that in DNA content (Mello et al. 1970). The Malpighian tubes of Melipona quinquefasciata, a stingless bee which has germinative polyploid cells, show the same DNA content per nucleus as those of Melipona quadrifasciata (Mello and Silveira 1970).