Cadmium cytotoxicity and variation in nuclear content of DNA in Euglena gracilis [cadmium resistant, growth]
1980
Bonaly, J. | Bariaud, A. | Duret, S. | Mestre, J.C. (Paris-11 Univ., 92, Chatenay-Malabry (France). Lab. de Biologie Cellulaire)
Cultures of Euglena gracilis (strain Z from French CNRS collection) can be made cadmium resistant if grown in a medium with 5 x 10('-4)M cadmium chloride. This resistance is reflected by the appearance of a second exponential growth phase. The development of this resistance was studied at the cellular level by determining the relative content of DNA at different stages of the cell cycle in an asynchronously grown culture. The culture was followed until the second, cadmium resistant, growth phase had reached its stationary state. During the first exponential growth phase, cells were mostly in the late period of DNA synthesis (stage S of the cell cycle), or in the gap preceding mitosis (stage G(,2) of the cell cycle). In addition some cells contained high multiples of the normal amount of DNA. In the beginning of the second exponential growth phase a few cells were again in G(,1) (the post mitotic stage of the cell cycle preceding DNA synthesis). These G(,1) cells were predominant at the end of the second growth period. During the second stationary phase the DNA content of the cadmium treated cells was similar to the stationary phase of the control culture. Cells had stopped growing in G(,1) with an unreplicated genome. The implications of these data are discussed.
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