NUCLEIC ACID AND PROTEIN METABOLISM DURING THE MITOTIC CYCLE IN VICIA FABA

Abstract

A B S T R A C TIn order to investigate some of the cytochemical processes involved in interphase growth and culminating in cell division, a combined autoradiographic and microphotometric study of nucleic acids and proteins was undertaken on statistically seriated cells of Vicia faba root meristems. Adenine-8-C x4 and uridine-H ~ were used as ribonucleic acid (RNA) precursors, thymidine-H 3 as a deoxyribonucleic acid (DNA) precursor, and phenylalanine-3-C 14 as a protein precursor. Stains used in microphotometry were Feulgen (DNA), azure B (RNA), pH 2.0 fast green (total protein), and pH 8.1 fast green (histone). The autoradiographic data (representing rate of incorporation per organelle) and the microphotometric data (representing changes in amounts of the various components) indicate that the mitotic cycle may be divided into several metabolic phases, three predominantly anabolic (net increase), and a fourth phase predominantly catabolic (net decrease). The anabolic periods are: 1. Telophase to post-telophase during which there are high rates of accumulation of cytoplasmic and nucleolar RNA and nucleolar and chromosomal total protein. 2. Post-telophase to preprophase characterized by histone synthesis and a diphasic synthesis of DNA with the peak of synthesis at mid-interphase and a minor peak just preceding prophase. The minor peak is coincident with a relatively localized DNA synthesis in several chromosomal regions. This period is also characterized by minimal accumulations of cytoplasmic RNA and chromosomal and nucleolar total protein and RNA. 3. Preprophase to prophase in which there are again high rates of accumulation of cytoplasmic RNA, and nucleolar and chromosomal total protein and RNA. The catabolic phase is: 4. The mitotic division during which there are marked losses of cytoplasmic RNA and chromosomal and nucleolar total protein and RNA.A primary area of cytology concerns the complex and periodic physiological changes that accompany the mitotic cycle. It has become increasingly evident that much of the mitotic process involves a utilization and segregation of materials synthesized during the preceding interphase. It would seem, therefore, that a study of the time and rate of synthesis in the mitotic cycle of the major nucleoprotein fractions of the cell, would form one approach to an understanding of mitosis and interphase growth. In the present study, the nucleoproteins of the nucleolus, chromosomes, and cytoplasm have been studied using both microphotometric and autoradiographic methods. A study of this kind may be made on a homogeneous tissue, the cells of which are undergoing a division cycle which is synchronous, or if non-synchronous, cells may be related to time in one of a number of ways: seriated by selection of cells at the same stage of mitosis (Prescott, 1955) synchronized by tempera-

Contraction of chromosomes and depression of RNA synthesis by isopropyl N-(3-chlorophenyl) carbamate (CIPC) in Vicia faba root tip cells.

“…It is well known that the active synthesis of RNA occurs only in the interphase stage or early prophase stage, diminishes near the onset of mitosis, then ceases while the chromosomes are in a strongly condensed state (Woodard et al 1961, Van't Hof 1963, Davidson 1964, and Das et al 1965. Hence most of labeled RNA at metaphase figures after the prolonged incorporation time was formed during earlier stages while the nuclei were active in RNA synthesis (Das et al 1965).…”

Duration of Mitotic Cycle and Patterns of DNA Replication in Chromosomes ofAllium Cepa

“…The fact is not particular to Allium cepa but has been described in other plants such as Fritillaria lanceolata (PELC and LA CouR 1959), Secale cereale (LIMA-DE-FARIA 1959b;DARLINGTON and HAQUE 1966), Vicia faba (LACouR and PELC 1958;WooDWARD et al 1961;EvANS 1964 MoRISHIMA et al 1962, for man). That difference of DNA synthesis between euchromatin and heterochromatin is likely to correspond to a general phenomena, despite of the heterogenous nature of heterochromatin in plant and animal organisms.…”

The Relationship between the Kinetics of Ribonucleic Acid Accumulation and the Morphological Development of the Fern Gametophyte, Dryopteris borreri

“…The DNA content of the dividing cell doubled prior to mitosis whereas the RNA content increased greater than 3-fold. A similar 3-fold increase in cytoplasmic RNA has been observed in the root tip meristematic cells of Vicia faba (30). The histochemical studies on D. borreri gametophytes show that following this "overproduction" of RNA in the initial division, the cell "underproduces" RNA for subsequent divisions with the result that the RNA content of the apical cell decreases (Fig.…”