EXTREME ALTERATION OF THE NUCLEOCYTOPLASMIC RATIO IN STENTOR COERULEUS.

Abstract

SYNOPSIS. Nucleocytoplasmic relationships were explored by producing the extreme alterations in proportion of macronucleus to cytoplasm for which the ciliate Stentor coeruleus is uniquely suitable. Cytoplasmic volumes were varied from about 40 to 6000 times the nuclear volume, as compared with a normal range of approximately 126 to 387. 1. Neither gross reduction nor great excess of the nuclear complement stimulate or inhibit cell division; for division never promptly ensued nor were giant cells or dwarf lines produced. Previous studies(5) have shown that lesser variations in nucleocytoplasmic proportions also have none of these consequences. 2. Hypernucleation produces no noticeable accelerating effect on cell re‐differentiation (oral regeneration), ciliary activity (swimming and feeding), or growth and multiplication. 3. Overnucleation is adjusted by extensive fusion of macronuclear nodes (reducing nuclear surface area) and by gradual resorption of some of the nucleus. 4. Nucleus maximally reduced to one node in normal and greater amounts of cytoplasm almost always results in delays of 2 to 15 times the usual preparatory period for regeneration as well as diminished feeding and impaired digestion, and acts as a stimulus to reorganization—confirming Schwartz(27). In hyponucleates there is a compensatory increase in nodal number following regeneration, reorganization (or division), but only after oral primordium formation—again confirming Schwartz. At least two such formations (regeneration followed by reorganization or division) are required for recovery of a nuclear complement of normal proportions, and this very probably represents a true increase in macronuclear substance as well as in number of nodes.6. In division the number of macronuclear nodes is approximately doubled, such that each fission product begins with about the same number as the parent cell, but the new nodes are generally smaller. Whether, during interfission, a regular increase in size of nodes and the addition, at most, of 3 new nodes represents a real increase in nuclear substance is questionable in view of the fact that isolated single nodes remain as such for days without increase until oral primordium development. Cytosomal events may be said to give the stimulus to renodulation and possibly also to macronuclear growth as they do for micronuclear growth in mitosis.7. When the nucleus is maximally reduced, the single node may be resorbed and no oral regeneration occurs. Alternatively, the macronuclear bead supports delayed regeneration but fails, temporarily or permanently, to increase itself. Less commonly, neither oral nor nuclear regeneration occurs though the single node persists. All indicate a statistical probability of some injury to a reduced nucleus when in an excess of cytoplasm. 8. Early oral primordia are resorbed in regenerators (and dividers and reorganizers) when the macronucleus is reduced to one node, but the single node which could not support continued regeneration is nevertheless sufficient for subsequent re‐regeneration. 9. At most the oral primordium can develop 3 steps further (more often 2, sometimes none) after complete enucleation. Hence there is little storage of nuclear support. Stage‐5 anlagen, still without visible trace of mouth‐parts, can develop fully, suggesting there is little synthesis of materials in later development but largely morphogenetic movements of invagination and translocation in completion of the feeding organelles.10. Enucleated stentors can feed quite well at first but not at all later. All indications are that they are incapable of digesting food organisms. Mononodal stentors fare somewhat better and recover normal function as they regenerate the nuclear chain. Enucleates die on the average sooner than starved nucleate controls, but there is considerable overlap in survival times.Some inferences from these findings are discussed. In experiments with other concerns, a sufficient amount of macronucleus should be used or retained, else the disproportion becomes a factor in itself.