Effect of temperature on dry mass of polytene nuclei in Drosophila

Nuclei were isolated by an aqueous detergent method from Drosophila prepupal salivary glands, and measured by integrating interference microscopy. There was a highly significant correlation between nuclear volume and dry mass. Dry masses fell into 2, 3 or 4 distinct groups corresponding to polytene replication classes; the mean of a given dry mass group was between 8 and 30% less than twice that of the group below, indicating that the ratio of DNA:dry mass increases during polytenic growth. The proportion of nuclei in the higher mass groups, the mean dry mass of nuclei within a given mass group, and the percentage loss of nuclear dry mass in the first hour after isolation were all higher when animals were reared at 15 degrees instead of 25 degrees C. Nuclear dry mass in prepupae was affected by the temperature during both the embryonic and larval periods, and also to some extent by the nutrition and degree of crowding of the cultures.