Elementary Statistics with Applications in Medicine and the Biological Sciences. By Frederick E. Croxton. Pp. vii, 376. $1.95. 1959 (Dover Publications, Inc., New York.)

Publisher Summary This chapter summarizes about the cell life cycle. An effort has been made to integrate the information into a general scheme of operation for the cell cycle with comments about mechanisms that may provide for cycle continuity and for interruption of the cycle in the regulation of cell reproduction. Cell cycle continuity is considered to be based on the sequential transcription and translation of the set of cell cycle genes that are held in temporal order by the activation of one cell cycle gene, by the function of an antecedently activated gene. The outlines of the cell cycle have been established, and this has led to clearer definition of the problems of cell growth and reproduction. The major tasks are to determine the basic causal sequence of molecular events that underlies the procession of G,-S-G2-D, to explain how the many, various growth activities participate in or are coordinated with this procession, and to discover how the cycle is arrested in G, to provide regulation of cell reproduction.

The Cell Cycle and the Control of Cellular Reproduction

Introduction Quiescent and dormant embryos, germination: definitions Nuclear characteristics of the cell population in quiescent embryos Distribution of quiescent embryo cell nuclei in different phases of the cell cycle How is the high G\\ cell level of quiescent embryos established? What are the mechanisms controlling G\\ cell accumulation? Controversial observations on the high G\\ accumulation in quiescent embryos Asynchrony of the first mitotic cycle The problem of dry tissue fixation Ultrastructure and cytochemistry of the nucleus in quiescent and early germinating embryos Shape of the nucleus Chromatin in quiescent embryos Possible factors responsible for chromatin condensation in quiescent embryos Dehydration Ions HistoneHl Poly(ADP-ribose) polymerase Chromatin during early germination Possible relationship between chromatin dispersion and its activity Transcription DNA replication and DNA repair RNP translocation Nucleoplasmic ribonucleoproteins Are nucleoplasmic RNPs the storage form of long-lived mRNAs? The nucleolus Ultrastructure Vacuolation Possible significance of nucleolar RNP loss during early germination

Nuclear activation during early germination of the higher plant embryo.

A Strong Nucleotypic Effect on the Cell Cycle Regardless of Ploidy Level

Characteristics of root apical meristem cell population kinetics: A review of analyses and concepts

SUMMARYThe study of the onset of DNA synthesis and mitosis in the germinating onion reveals that the first few millimeters of root growth occur exclusively as a result of cell expansion. DNA synthesis and mitosis are initiated at the 1.4 and 2.8 mm. stages of growth, respectively. Stable indices are attained at approximately 7.0 mm. in the case of DNA synthesis, and 10.0 mm. for mitosis. Timing of both points of initiation suggests an S plus G2 interval of 9.2 hours, and labelling indices indicate that S is not quite three times as long as M. The work demonstrates that emergent root length is a reliable external criterion for the timing of internal cellular events.

https://www.tandfonline.com/doi/pdf/10.1080/00087114.1969.10796331

DNA Synthesis and Cell Division in Germinating Onion I. Onset of DNA Synthesis and Mitosis

SUMMARYThis study of the duration of the mitotic cycle in the germinating onion shows a mitotic cycle at stability of 12.8 hours, with G1, S, G2, and M-periods of 1.5, 6.5, 2.4, and 2.3 hours, respectively. Phase durations are 0.8, 0.2, 0.1, and 1.2 hours for prophase, metaphase, anaphase, and telophase, in that order. When examined as a function of developmental stage, no significant variation is seen in the lengths of the above intervals. Microspectrophotometric analysis of various developmental stages reveals that the total nuclear complement of the quiescent embryo is in G1, (essentially all 2C), and that the initiation of DNA synthesis occurs at approximately the 1.5–2.0 mm. point in root development, in agreement with the value determined earlier.

https://www.tandfonline.com/doi/pdf/10.1080/00087114.1969.10796332

DNA Synthesis and Cell Division in Germinating Onion II. Mitotic Cycle and DNA Content

SUMMARYCareful microspectrophotometric analysis of the 2C (Gl) nuclear population of the onion during the critical period of decompaction from the quiescent to the functional state reveals an increase in apparent DNA content correlated with increased nuclear area. This finding is demonstrated not to depend on technical flattening of nuclei, but on the state of chromatin condensation. The probable identity of this phenomenon with that recently reported from mammalian systems is discussed, as are the possible interpretations of cause. It is provisionally concluded that current evidence favors the view that the relationship reflects non-stoichiometric stain-substrate interaction. The relative advantages of the onion system for future work in this area are discussed.

T. R. Bryant

Papers

DNA Synthesis and Cell Division in Germinating Onion I. Onset of DNA Synthesis and Mitosis

DNA Synthesis and Cell Division in Germinating Onion II. Mitotic Cycle and DNA Content

DNA Synthesis and Cell Division in Germinating Onion: III. Variation in Apparent Feulgen-DNA Content with Nuclear area Change