POLYTENE CHROMOSOMES IN THE CILIATE EUPLOTES WOODRUFFI
WANG HA-LI, CHEN YUE-ZENG (Department of Biology, Peking University, Beijing 100871, China)
By means of optical and TEM, the development of the macronuclear anlage and the structure of the polytene chromosomes of the exconjugants of Euplotes woodruffi, were investigated. The macronuclear anlage in the young exconjugants newly separated from the mating pairs was homogeneous and only faintly stained with Feulgen's reagent or carbol- fuchsin. In 4-5 hours exconjugants, granular chromosomes appeared which elongated soon into vermiform rodlets. The number of chromosomes was counted as 2n = 70-90. After about 20 minutes, bands of various sizes began to appear in all the chromosomes in the anlage. It seemed that polytenization and despiralization occurred simultaneously in the chro- mosomes. In exconjugants of more than 5 hours old, chromosomes extended to over 60 μm in length and showed clearly differentiated bands and interbands. Fan-shaped and node-like ends of some chromosomes were seen. Densely stained spherical bodies, believed to be centromeres, were also present in some of the preparations. When the anlage arrived at the largest size with polytene chromosomes densely packed in it, the DNA contents increased to maximum, i. e., about one half the DNA contents of the vegetative macronucleus. Polytene chromosomes were then cut by fibrillar membrane of the nature of intermediate filaments into fragments and the DNA contents of the anlage dropped to minimum, i. e., about one tenth of the maximum amount, concurrently.