蝗虫复眼小网膜细胞角敏感度的变化规律

在不同时间(上午、下午和晚上)和不同适应状态(暗适应和三种不同背景光强度的明适应)下,利用细胞内记录方法测量蝗虫复眼不同区域(背、侧和前区)小网膜细胞的角敏感度,其大小随着复眼区域、适应状态和24小时的周期性变化而变化.     

几种激素在鳜胃肠道内分泌细胞中存在的免疫细胞化学证据

用链酶亲和素－生物素过氧化物酶（Strept Avidin-Biotin-Complex,SABC）免疫细胞化学方法,使用4种兔抗消化 道激血清对鳜胃肠道中的内分泌细胞进行鉴别和定位。结果在鳜鱼胃的贲门、幽门及肠道中均发现不同程度地存在着生长抑素和五羟色胺免疫活性内分泌细胞。在鳜的贲门上皮和贲门腺之间,幽门上皮和幽门腺之间均分布有生长抑素免疫活性阳性细胞,在贲门腺和幽门腺处的分布较密。这些含五羟色胺的肽能神经元具有典型的APUD（Amine Precursor Uptake and Decarboxylation）细胞特征,提示鱼类的胃肠道同哺乳动物的胃肠道一样富含肽能神经元;为神经－内分泌系统的研究提供有力的形态学依据,另外两种抗血清－高血糖素和胃泌素的免疫细胞化学染色在鳜的胃肠道的各部位均未发现阳性反应。     

FURTHER EVIDENCE FOR OSMOREGULATION IN EPIDERMAL LEAF CELLS OF SEAGRASSES

A comparison of the epidermal leaf cell ultrastructure of three seagrasses, Thalassia testudinum (tropical, high salinity), Zostera marina (North temperate, moderate salinity), and Ruppia maritima (North temperate, brackish) provides confirmation for the theory that an invaginated plasmalemma-mitochondrial transport system is developed at least in part as a response to salt concentration. Cytochemical localization of presumed Cl⁻ ion provides further evidence for the presence of a salt secretion or exclusion mechanism. Immature epidermal leaf cells communicate with each other and with mesophyll cells through numerous plasmodesmata, but during cell maturation these cytoplasmic connections are lost and the apoplastic transport system develops to replace the symplastic one. The two North temperate region seagrasses contain cytoplasmic lipids which are absent in the tropical species. Thalassia and Zostera have chloroplasts which lack starch, but stain densely for polysaccharides with thiocarbohydrazide. The polysaccharide staining is essentially negative in the chloroplasts of Ruppia, but mesophyll chloroplasts of this brackish water species contain starch. These and other cytological findings are compared with other seagrasses.     

EVIDENCE FOR CYTOPLASMIC DNA IN ROOT CELLS OF NICOTIANA

Sterile root cultures from Nicotiana tabacum were grown with H³-thymidine added to the medium for various intervals. Incorporation of the labeled nucleoside into nuclear DNA occurred in a fraction of the nuclei which increased with time. In addition, the cytoplasm of all cells incorporated enough tritium to be readily detected by autoradiography. The tritium was not removed by hydrolysis in 1 N HCl at 60°C for 10 minutes, but was removed by digestion in a DNase solution which also removed nuclear DNA. The amount of tritium in the cytoplasm increased during the first 2 hours, but did not appear to increase significantly during the following 5 hours. If the roots were transferred to unlabeled medium after 2 hours, the label was diluted faster than expected by growth without turnover of the labeled component. If FUdR was added to the unlabeled medium, the depletion occurred faster during the first 6 hours, but later appeared to level off so that at 10 hours these cultures did not differ from those incubated without FUdR. However, the addition of an excess of unlabeled carrier had no effect on the rate of depletion of the cytoplasmic label. Actinomycin D, which inhibited the incorporation of H³-cytidine into RNA in the root tips, had no effect on the incorporation of H³-thymidine into the cytoplasmic component. However, Mitomycin C or a high concentration of deoxyadenosine inhibited the incorporation of H³-thymidine into the cytoplasmic component as well as into the nuclear DNA. It is concluded that H³-thymidine is incorporated into a cytoplasmic fraction which has the characteristics of DNA, with a measurable rate of turnover. This fraction is synthesized regardless of whether or not the nucleus is synthesizing DNA. Although the function of cytoplasmic fraction is not yet known, it does not appear to be that of supplying precursors for the synthesis of the nuclear DNA.     

EVIDENCE FOR APICAL INITIAL CELLS IN THE VEGETATIVE SHOOT APEX OF HEDERA HELIX CV. GOLDHEART

We examined changes in the pattern of leaf variegation in a periclinal chloroplast chimera of Hedera helix L. cv. Goldheart to determine whether stable apical initials exist in the shoot apex. Additional data were obtained by histological analyses. All of the data indicate that four apical initials are present in the third layer of the apex, supporting the model of a structured apical meristem.     

EVIDENCE FOR THE PRESENCE OF LIGNIN IN MOSS GAMETOPHYTES

Lignin has been established as a constituent of the gametophyte axes in the giant New Zealand mosses Dawsonia sp. and Dendroligotrichum sp. Isolated products comprised ca. 6-10% of the dry weight of gametophyte axes and contained 61-62% C, 6.4-6.8% H, and 5.1-7.9% OCH₃. Characteristic color reaction and ultraviolet spectra were observed, and alkaline nitrobenzene oxidation yielded perhaps 14-18% of mixed aldehydes as their 2,4-dinitrophenylhydrazones. The presence of substantial lignin in these exceptionally tall upright moss gametophytes contrasts strikingly with north temperate species such as Polytrichum, Funaria, Bryum and others, and lends support to the hypothesis that lignification is a mechanically and/or gravitationally regulated process.     

EVIDENCE OF DIFFERENCES IN THE DESOXYRIBONUCLEOPROTEIN COMPLEX OF RAPIDLY PROLIFERATING AND NON-DIVIDING CELLS

1. Quantitative cytophotometric analysis of the interphase cells of a rapidly proliferating differentiated tissue such as liver of new born rat, indicates that these cells can be separated into two groups on the basis of their staining characteristics after methanol fixation. 2. These groups are thought to correspond to two stages of interphase. The first, called "autosynthetic interphase," comprises cells which are duplicating chromosomal material in preparation for mitosis, and shows parallel increases in the methyl green and Feulgen staining of DNA and the fast green staining of histone from the diploid (2 C) to double these values (4 C). 3. The second group is designated the "heterosynthetic interphase," during which the cell ceases proliferating and functions in a manner commensurate with its state of differentiation. In this stage Feulgen staining indicates the diploid chromosomal complement, but there is a decreased capacity of the DNA to bind methyl green and of the histone to bind fast green. 4. The difference between the methyl green binding of the heterosynthetic and autosynthetic 2 C cells is due to the presence of a protein in the former which presumably inhibits staining by competing with the dye for binding sites on the DNA. The effect of this inhibition can be removed by extracting the protein, or by blocking the protein basic groups. 5. The decreased fast green staining of histone in the heterosynthetic cells can be minimized by prolonged fixation with formaldehyde. It is thought to stem either from a similar type of inhibition, or from an increased susceptibility of the histone to loss from the cell during this stage. 6. While histone inhibits methyl green staining of DNA in all cells, the differences between the staining properties of the autosynthetic and heterosynthetic interphase cells are believed to be due to another protein, whose properties appear similar to those of the chromosomal "residual protein." It is concluded that a complex of DNA and residual protein existing during the heterosynthetic interphase is dissociated during the autosynthetic interphase.     

ANOMALOUS STIMULATION OF PROTEIN SYNTHESIS: EVIDENCE FOR TRANSLATIONAL CONTROL IN PRIMARY CELLS

Chick cells in primary culture synthesize protein at an accelerated rate following recovery from prolonged (2-12 hr) inhibition of protein synthesis. This 'overshoot' is followed by a return to the normal rate of synthesis.
Both actinomycin and fluorophenylalanine provided during the recovery period enhance the 'overshoot' and prevent the return to normal.
The results are consistent with the proposal that protein synthesis is restricted by an inhibitor or 'governor', itself a protein of relatively short half life.
Neither L nor HeLa cells demonstrate an 'overshoot' during the recovery phase.     

EVIDENCE FOR PLEIOTROPIC CHANGES IN LINES OF CHINESE HAMSTER OVARY CELLS RESISTANT TO CONCANAVALIN A AND PHYTOHEMAGGLUTININ-P

Lines of Chinese hamster ovary cells resistant to the lectins concanavalin A (Con A) and phytohemagglutinin-P (PHA-P) have been isolated and characterized. Lines were isolated by a stepwise, a single-step, or a cycling single-step procedure, from both mutagen-treated and untreated cultures. The resistant lines showed a higher efficiency of colony formation in the presence of the appropriate lectin than did the wild-type parental line. The cell lines resistant to Con A did not exhibit any detectable cross resistance to PHA-P, nor did the PHA-resistant cells exhibit cross resistance to Con A. The toxicity of Con A from the wild-type and Con A-resistant lines was reduced in the presence of methyl α-D-glucopyranoside; this effect was not seen with the PHA-resistant line. Using ¹²⁵I-labeled Con A, it was found that Con A was bound preferentially to the surface of intact cells, and that the amount of labeled Con A bound to intact cells was similar for the wild-type and lectin-resistant lines. The Con A-resistant lines were found to be more susceptible to the toxic effects of a number of different compounds, including cyclic AMP and its dibutyryl derivative, sodium butyrate, high concentrations of glucose, phenethyl alcohol, phenol, ouabain, and testosterone. It appears that, in these lines, acquisition of resistance to Con A gave rise to pleiotropic effects which were detected by changes in the sensitivity of the cells to a variety of agents.     

EVIDENCE FOR THE CLOSE ASSOCIATION OF A GLYCOPROTEIN WITH MYELIN IN RAT BRAIN

Abstract— Myelin was purified from rats which had been injected intracerebrally with radioactive fucose in order to label specifically the glycoproteins. Myelin contained a small amount of fucose-labelled glycoproteins in comparison to that in other subcellular fractions, but polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate revealed a unique pattern of radioactive glycoproteins dominated by a major peak. The same glycoprotein was not prominent in the other subcellular fractions which were examined. This major glycoprotein in the myelin fraction was also labelled after injection with [³H]glucosamine or N -[³H]acetylmannosamine. It was the most intensely staining myelin protein when gels were treated with periodic acid-Schiff reagents, an indication that, in terms of protein-bound carbohydrate, it is the major glycoprotein in the myelin fraction. The glycoprotein was present in myelin purified from rats ranging in age from 14 days to 14 months. Extensive recycling of the myelin through the purification procedures did not significantly reduce the amount of glycoprotein in the myelin. Double label experiments with [³H]fucose and [¹⁴C]fucose were used to compare glycoproteins in myelin purified from white and grey matter, respectively, and from mixed homogenates of myelinated and unmyelinated brain. The results obtained from these experiments suggested that the glycoprotein is closely associated with myelin and that it is not in an unrelated contaminating structure. Possible locations of the glycoprotein are discussed. They include the myelin membrane itself, the oligodendroglial plasma membrane, and the axolemma of myelinated axons.     

FURTHER EVIDENCE FOR THE PRESENCE OF A PANETH CELL PROGENITOR IN MOUSE INTESTINE

Photomicrographic evidence, mitotic figures and ³H-thymidine labeling among Paneth cells, is presented in support of the hypothesis that Paneth cells are replaced by cells proliferating in the bottom of the intestinal crypt rather than by migration of cells from the mid-crypt region.     

A NOTE ON THE UNUSUAL CRUSTACEAN COMMUNITY OF A TEMPORARY POOL IN THE NORTHERN CAPE

Summary

A temporary pool in a dry stream bed traversing Grootvloer Pan in the Northern Cape was inhabited by fifteen branchiopod and calanoid copepod crustacean species. There was an unusually high number of congeneric species in the pool; in the class Branchiopoda, five Streptocephalus species and four Daphnia species were collected. In addition, two species of the calanoid genus Metadiaptomus were identified. The high species richness was not related to habitat diversity, pool size or difference in body size of each species. Three species (Streptocephalus purcelli, S. gracilis and Metadiaptomus capensis) had previously been collected only from the winter-rainfall areas of the Cape. Episodic flooding in the Northern Cape in 1988 may have resulted in the unusual community in the Grootvloer temporary pool.     

A POSSIBLE MECHANISM FOR THE MORPHOGENESIS OF LAMELLAR SYSTEMS IN PLANT CELLS

A mechanism for the formation of lamellar systems in the plant cell has been proposed as a result of electron microscope observations of young and mature cells of Nitella cristata and the plastids of Zea mays in normal plants, developing plants, and certain mutant types. The results are compatible with the concept that lamellar structures arise by the fusion or coalescence of small vesicular elements, giving rise initially to closed double membrane Structures (cisternae). In the chloroplasts of Zea, the cisternae subsequently undergo structural transformations to give rise to a compound layer structure already described for the individual chloroplast lamellae. During normal development, the minute vesicles in the young chloroplast are aggregated into one or more dense granular bodies (prolamellar bodies) which often appear crystalline. Lamellae grow out from these bodies. In fully etiolated leaves lamellae are absent and the prolamellar bodies become quite large, presumably because of inhibition of the fusion step which appears to require chlorophyll. Lamellae develop rapidly on exposure of the plant to light, and subsequent development closely parallels that seen under normal conditions. The plastids of white and very pale green mutants of Zea similarly lack lamellae and contain only vesicular elements. A specialized peripheral zone immediately below the double limiting membrane in Zea chloroplasts appears to be responsible for the production of vesicles. These may be immediately converted to lamellae under normal conditions, but accumulate to form a prolamellar body if lamellar formation is prevented, as in the case of etiolation and chlorophyll-deficient mutation, or when the rate of lamellar formation is slower than that of the production of precursor material (as appears to be the case in the early stages of normal development).     

EVIDENCE FOR A CRYPTOMONAD SYMBIONT IN THE CILIATE,CYCLOTRICHIUM MEUNIERI1

Extracts of the marine ciliate Cyclotrichium meunieri contained chlorophylls a and c, carotenoids, and a phycoerythrin with a single absorbance maximum at 542 nm. This assemblage of pigments suggests that the numerous photosynthetic symbionts present in each ciliate cell belong to the Cryptophyceae.