用DNA过量核酸分子杂交法对大鼠肝和大鼠肝癌细胞核RNA的比较研究

用DNA过量核酸分子杂交法观察到,大鼠肝癌细胞中重复频率在10~4以上的Poly(A)-核RNA的频率和种类,均比大鼠正常肝细胞有所增加。大鼠肝癌细胞中重复频率在1—4×10~2的Poly(A)-核RNA和Poly(A)~+核RNA的重复频率,比大鼠正常肝细胞减少,而RNA种类则增加。大鼠肝癌细胞中,接近单拷贝的Poly(A)-核RNA和Poly(A)~+核RNA,其频率比大鼠正常肝细胞略有增加,而种类则减少。用总细胞核RNA得类似结果。     

A COMPARISON OF THE HETEROGENEOUS NUCLEAR RNA OF HELA CELLS IN DIFFERENT PERIODS OF THE CELL GROWTH CYCLE

HeLa cells synthesize heterogeneous nuclear RNA (HnRNA) in the G₁, S, and G₂ portions of the cell cycle. HnRNA prepared from these various periods was compared by RNA-DNA hybridization experiments. The results indicated that some of the HnRNA molecules were equivalent at all times in the cell cycle, but limitations in the sensitivity of the hydridization reactions, as well as in the spectrum of hybridizing molecules, restrict the conclusions that can be drawn from these comparisons.     

NUCLEAR MEMBRANES OF CULTURED MAMMALIAN CELLS IN THE PERIOD PRECEDING DNA SYNTHESIS

When kidney cells are cultured directly from the rabbit, the nuclear membranes undergo a change that can be measured as an increase in electrophoretic mobility. The change appears to begin immediately upon culture and is maximal 2 hours later, after which the mobility remains constant at the elevated level. Actinomycin D and p-fluorophenylalanine, but not EDTA or ionizing radiation, suppress the increase in nuclear electrophoretic mobility. With synchronously growing L cells, no change was detected in nuclei from cells taken during various parts of the division cycle.     

THE SYNTHESIS OF PHOSPHOLIPIDS IN THE NUCLEUS AND NUCLEAR MEMBRANE OF SYNCHRONIZED HeLa CELLS

HeLa cells were synchronized by a double thymidine block and pulse labeled at different stages of the cell cycle with ³H-choline. The specific activity of phospholipids extracted from the cell, the nucleus and the nuclear membrane showed a progressive increase from S to G₁; the incorporation of choline into phospholipids of asynchronous cells showed a specific activity intermediate between the values of S and G₁ cells. Similar results were obtained when ³²phosphorus was used as a precursor instead of choline. Thin layer chromatographic analysis of phospholipids extracted from cells in S and from cells in G₁ failed to show any difference in the distribution of radioactivity among the various phospholipid classes. Choline uptake by HeLa cells in different phases of the cell cycle did not show significant variations. However, during the synchronization process, shortly after the addition of excess thymidine, an increased uptake of choline by cells and an increased incorporation of choline into phospholipids were found. The results indicate that some of the changes occurring in phospholipids synthesis may not be cell cycle dependent, but may be the effect of the synchronizing process.     

PHYLOGENETIC SYSTEMATICS OF THE ULVACEAE (ULVALES,ULVOPHYCEAE) USING CHLOROPLAST AND NUCLEAR DNA SEQUENCES1

Systematic hypotheses for the Ulvaceae were tested using phylogenetic analysis of sequences for the gene encoding the large subunit of RUBISCO, small subunit rDNA and a combined data matrix. Representatives of eight putative ulvaceous genera and twelve additional taxa from the Ulvophyceae and Trebouxiophyceae were included in analyses using maximum parsimony and maximum likelihood criteria. Molecular data supported hypotheses for the Ulvaceae that are based on the early development of vegetative thalli and motile cell ultrastructure. Ulvaceae sensu Floyd and O'Kelly, including Percursaria Bory de Saint‐Vincent, Ulvaria Ruprecht and a complex of closely related species of Chloropelta Tanner, Enteromorpha Link and Ulva L. was supported; however, monophyly of Enteromorpha and Ulva was not supported. The Ulvales and Ulotrichales sensu Floyd and O'Kelly were monophyletic. Blidingia Kylin and Kornmannia Bliding were allied with the former and Capsosiphon Gobi with the latter, although relationships among these and other taxa in these orders remain uncertain. The Ulvales are characterized by an isomorphic life history pattern, gametangia and sporangia that are identical in structure and development, motile cells with bilobed terminal caps and proximal sheaths consisting of two equal subunits. Method of motile cell release and the gross morphology of vegetative thalli are not systematically reliable characters.     

THE NUCLEAR DNA CONTENT OF LARGE VENTRAL SPINAL NEURONS

Abstract— A nuclear fraction has been obtained from large spinal neurons previously isolated from bovine ventral spinal cord in bulk suspensions. The fraction contained an average of 5.3 ± 0.9 pg DNA/nucleus, indicating a high incidence of diploid nuclei. This conclusion was confirmed by distribution analysis of DNA in propidium iodide-stained nuclei examined by flow microfluorometry. That technique showed that at least 90% of the nuclei from large spinal neurons are diploid. Mixed, mostly non-neuronal nuclei derived from many types of cells in the ventral spinal cord contained an average of 5.9 ± 0.6 pg DNA/nucleus, 19% of which possibly possess more than diploid amounts of DNA. The uniform DNA content in nuclei of large spinal neurons and most other types of cells in the ventral spinal cord contrasts sharply with a wide variation (av 26-fold) in the nuclear volumes of the same cells.     

DNA CONTENTS IN PURKINJE CELLS AND INNER GRANULE NEURONS IN THE DEVELOPING RAT CEREBELLUM

Cytophotometric studies revealed that the content of Feulgen DNA in Purkinje cells in the developing rat cerebellum remains at the diploid level throughout the postnatal life. No evidence was found to suggest resumption of DNA synthesis in the neurons. This finding is in accord with autoradiographic observations that neuroblasts once differentiated from matrix cells do not synthesize DNA nor divide again.     

METABOLIC PRIORITIES WITH RESPECT TO GROWTH AND MINERAL UPTAKE IN ROOTS OF HORDEUM,TRITICUM AND LYCOPERSICON

Reduction in the supply of photosynthate to the roots of tomato, barley, and wheat plants was achieved indirectly by lowering the intensity of sunlight striking the foliage of test plants. The decrease in sugar and starch concentrations in the roots was verified by appropriate extraction and colorimetric analysis, and a corresponding reduction in the total respiratory rate of the roots was confirmed using an oxygen tension monitor. Other processes measured directly include the rate of uptake of potassium, the mitotic quotient in the root tip—a measure of growth—and the rate of accumulation of dry matter in the root. The study demonstrated that of the metabolic activities observed, root growth is the process first limited when the supply of photosynthetic fuel is decreased. Root growth was severely inhibited under conditions that did not significantly affect either the active uptake of potassium per gram of root or total respiration per gram of root. With greater restriction of photosynthesis, growth was completely halted while the uptake of potassium was strongly decreased and total respiration was still affected only moderately. As the light intensity is reduced significantly, most of the reduced energy supply in the root appears to be used in support of processes critical to maintenance of the organ and the organism.     

THE OCCURRENCE AND PHYLOGENETIC SIGNIFICANCE OF PUTATIVE PLACENTAL TRANSFER CELLS IN THE GREEN ALGA COLEOCHAETE

Following fertilization, zygotes of the green alga Coleochaete orbicularis, which are retained on the haploid thallus, first enlarge, then become covered with a layer of vegetative cells. Light microscopy and high-voltage electron microscopy revealed the presence of localized wall ingrowths in vegetative cells adjacent to zygotes. These covering cells resemble the gametophytic placental transfer cells of embryophytes in their morphology, location, and time of development. If Coleochaete cells with wall protuberances function as do placental transfer cells of embryophytes, their presence is evidence that photosynthates may be transported between haploid thallus cells and zygotes. Thus, a nutritional relationship between different phases of the life cycle, similar to that which occurs in embryophytes, may also have evolved in green algae. This first report of putative placental transfer cells in a green alga supports Bower's (1908) ideas concerning the origin of land plant sporophytes and alternation of generations. The presence or absence of cells with wall ingrowths in several species of Coleochaete was correlated with estimates of zygote-plant area ratios.     

THE NUCLEAR DNA CONTENT OF DEVELOPING BARLEY ALEURONE CELLS

The nuclear DNA content of developing barley aleurone cells was examined by Feulgen cytophotometry using the Cytophotometric Data Conversion (CYDAC) system. At no time in their development did aleurone cells exhibit a single peak corresponding to the triploid (3N) amount of DNA. Although considerable heterogeneity was observed at every stage of development, the mean nuclear DNA content approximately doubled from the earliest to the most mature stage.     

中国野生稻及栽培稻核糖体DNA第一转录间隔区序列分析及其系统学意义

用 PCR技术从产于我国的 3种野生稻和亚洲栽培稻的 2个亚种中特异地扩增和测序了 r DNA的第一转录间隔区。普通野生稻 (Oryza rufipogon)、药用野生稻 (O.officinalis)、疣粒野生稻 (O.granu-lata)和栽培稻的两个亚种 (O.sativa ssp.indica,O.sativa ssp.japonica)的 ITS1序列为 1 93bp、1 94bp、2 1 8bp、1 94bp和 1 94bp,它们的 G/ C含量为 69.3%～ 72 .7% ,序列中位点趋异率为 1 .5%～ 1 0 .6%。序列的相似性比较和简约性分支分析的结果表明 ,普通野生稻与栽培稻的两个亚种之间的亲缘关系最为密切 ;药用野生稻与普通野生稻和与栽培稻的两个亚种的相似性都为 82 % ,说明它与 AA基因组有一定的亲缘关系 ;疣粒野生稻与普通野生稻、药用野生稻和栽培稻两个亚种的亲缘关系相对较远 ,它在稻属中可能是一个系统地位较独特的类群。以 ITS1序列构建的 3种野生稻和 2个栽培稻亚种的系统发育关系与前人用同工酶、叶绿体 DNA、线粒体 DNA和核 DNA资料重建的稻属的系统发育关系基本一致     

TEMPERATURE-INDUCED CAVITIES AND SPECIALIZED PARENCHYMA CELLS IN THE VASCULAR CYLINDER OF PEA ROOTS

Pea seeds (Pisum sativum L.) of six cultivars were planted in the field, in the greenhouse, or in growth chambers, in five different media, in light or dark, and at various temperatures (10–32 C). Under all conditions above 15 C the central portion of the vascular cylinder, in all cultivars except “Ageotropum,” tended to form cavities in almost every primary root examined. These cavities then became filled by the ingrowth of specialized parenchyma cells (SP cells). The formation of cavities and SP cells was temperature dependent since the roots grown below 15 C always formed central metaxylem tracheary elements (MTEs), without cavities and SP cells. Cavities and SP cells did not form over the entire root length. When the roots were longer than 3 cm, they started to form cavities and SP cells and continued for an additional 10–30 cm. After that, late MTEs formed in the central vascular cylinder, and no cavities and SP cells occurred regardless of temperature. Within an individual root grown above 15 C, cavities and SP cells tended to form during periods of fast growth, while during periods of slow growth large central MTEs formed instead.     

THE ONSET OF MITOSIS AND DNA SYNTHESIS IN ROOTS OF GERMINATING BEANS

The time of onset of mitosis and DNA synthesis has been determined in roots of germinating seeds of Vicia faba. Mitosis is not initiated in all roots simultaneously. Dividing cells are seen 36 hr from the beginning of germination, but they are present in low frequency (0.02%). Dividing cells do not become frequent, i.e., occurring as 5% or more of all cells, until 56 hr, and it is not until 66–68 hr that all roots in a sample of 10 are mitotically active. DNA synthesis shows a similar sporadic beginning. It occurs in a few cells by 28 hr, and by 40 hr all roots exposed to ³H–thymidine show active incorporation. For most cells in these germinating roots DNA synthesis precedes mitosis. In one root in 10, however, some cells are unlabeled when they enter mitosis, indicating that they had spent the dormant period in the G₂ phase of the mitotic cycle. The presence of these cells determines whether or not roots show chromatid and chromosome aberrations following irradiation during germination.     

THE SYNTHESIS OF DNA, RNA, AND NUCLEAR PROTEIN IN NORMAL AND TUMOR STRAIN CELLS : III. Mouse Ascites Tumor Cells

Interferometric and photometric measurements have been made on replicating mouse ascites tumor cell cultures. From a study of the relations between successive physical measurements on individual cells, it was found that whereas the net syntheses of nuclear RNA and nuclear protein are closely associated during interphase, they are dissociated from DNA replication to a significant extent. These results agree with others reported in replicating cell strains derived from tumors. In auxiliary experiments an attempt was made to block the initiation of DNA synthesis by X-irradiation: although large amounts of nuclear protein accumulated in some cells in the absence of DNA synthesis, the inability to hold the DNA block for an interphase time prevented a quantitative analysis of the results.