[Cytofluorimetric research on the changes in the DNA content in the nuclei of Amoeba proteus during prolonged starvation and after refeeding]. / Tsitofluorimetricheskoe issledovanie izmeneniia soderzhaniia DNK v iadrakh ameb Amoeba proteus v khode dlitel'nogo golodaniia i pri vozobnovlenii pitaniia.

Dividing amoebae were manually selected from the culture of Amoeba proteus, and so groups of synchronously dividing (synchronized) amoebae were obtained. These synchronized amoebae were maintained without food. In spite of starvation, individual amoebae in some particular groups were seen to divide, whereas in other groups of amoebae there was no division at all. The starving amoebae died not earlier than 2 weeks after the last division. A relative DNA content in isolated nuclei has been determined cytofluorometrically for each of 6 groups of synchronized starving amoebae, unable to divide. The nuclei were isolated in different intervals after division (after the feeding was ceased): 1.0-1.5 h, 1 day and up to 13 days with 1-2 day intervals. In the all groups of amoebae DNA synthesis occurred on the first 1-2 days after division. The nuclear DNA content in amoebae of 3 groups increased more than two-fold as compared with the 1 h level, in other 3 groups the nuclear DNA content did not exceed the doubled 1 h level, but probably exceeded the doubled postmitotic level. Later on, the nuclear DNA content in starving amoebae of each group was seen to decrease by 16-20%. Amoebae of 3 of the 6 groups were given the food organisms (Tetrahymena pyriformis) 8 days after division (after cessation of feeding). 2-3 days after refeeding some of these amoebae divided, and the nuclear DNA content of the refed amoebae proved to be higher than that in amoebae that continued to starve. It is suggested that the decrease of DNA content in the nuclei of starving amoebae and the increase of DNA quantity in the nuclei of refed amoebae may result from degradation and induction of synthesis of specific extra DNA synthesized in amoeba nuclei during each cell cycle.

[DNA hyperreplication in the nuclei of Amoeba borokensis in the cell cycle]. / Giperreplikatsiia DNK v iadrakh ameb Amoeba borokensis v kletochnom tsikle.

The relative nuclear DNA contents were determined cytofluorometrically for several groups of synchronized Amoeba borokensis at the early and late interphase. In some groups of these amoebae the nuclear DNA content by the end of the interphase exceeded more than twice that measured 1 h after division, when DNA in amoebic nuclei already being synthesized. This means that the extra DNA was synthesized in the nuclei of amoebae of these particular groups. In other amoebic groups the nuclear DNA content checked at the end of the interphase did not exceed the doubled 1 h level. Thus, in these amoebae the quantity of the synthesized extra DNA was less than that in the former groups, or the extra DNA was not synthesized at all.

[Relationship of the DNA content in the nuclei of Amoeba proteus to the food regimen]. / Zavisimost' soderzhaniia DNK v iadrakh Amoeba proteus ot pishchevogo rezhima.

The relative DNA content of isolated Amoeba proteus nuclei has been measured by cytofluorometry. With the amoeba strain studied, the generation time is roughly equal to 48 hours at 25 degrees C, and with the presence of food in the medium. After the synchronous divisions, amoebae were maintained in the medium either with or without food organisms (Tetrahymena pyriformis). DNA contents in the nuclei of both the amoebae groups were measured within 4 and 48 hours after division. Before 16 hours, the nuclear DNA contents did not differ in either group. Starting from 20 hours, the DNA amount in fed amoebae exceeded that in starved animals. On the whole, the differences in DNA quantity increased by a 48th hour after division, when the nuclei of the former contained 145% DNA of the latter. The results obtained suggest that the DNA synthesis in amoeba nuclei may proceed during the whole interphase, and that during the second half of interphase the content of DNA may depend on the feeding intensity in amoebae. After refeeding the starved animals, DNA contents in their nuclei increased to reach the same level as in the constantly fed amoebae seen in the end of interphase.