Journal of Cell Science, Vol 6, 351-363, Copyright © 1970 by Company of Biologists

Submitted on June 9, 1969

Organization and Development of the Macronuclear Anlage in Stylonychia Notophora Stokes

¹ Department of Zoology, University of Delhi, Delhi-7, India

The development of the macronuclear Anlage of Stylonychia notophora was studied by means of cytochemical and autoradiographic techniques. In early stages of its differentiation, the Anlage has its chromatin distributed homogeneously. Nine to ten hours later chromosomes are noticed; the nucleus is possibly diploid. Following this, the number of chromosomes increases progressively resulting in polyploidy. Later, chromosomes uncoil and polytenization follows. After consolidation and shrinkage of these chromosomes, the Anlage splits into two bodies. Five series of replication bands quickly pass through each and the vegetative macronucleus results.

Synthesis of RNA by the new macronucleus starts soon after the shrinkage stage.

The old macronuclei break up into small spherical bodies which are gradually resorbed in the cytoplasm.

When [³H]thymidine is provided continuously to the exconjugants, there is little uptake into the Anlage until the old macronucleus is completely resorbed. Only after this, heavy labelling is noticed. Fate of the previously labelled macronuclei during conjugation shows that their breakdown products are re-utilized for the development of the new macronucleus.