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1.
FREAN, M. L. & MARKS, E., 1988. Chromosome numbers of C3 and C4 variants within the species Alloteropais semialata (R.Br.) Hitch. (Poaceae). In a study of mid-lamina leaf sections, different variants of A. semialata were found to have C3 or C4 anatomy. The C4 leaf showed a specialized photosynthetic vascular bundle sheath not present in the C3 form. Chromosome counts made from pollen mother cell squashes showed that the C3 form of A. semialata is a fertile diploid 2n = 2x = 18 and the C4 form, a fertile allohexaploid 2n = 6x = 54. The cytological evidence suggests that the two forms should be considered as separate species.  相似文献   

2.
Abstract: We report here the molecular cloning of three new splice variants of the human serotonin 5-hydroxytryptamine4 (h5-HT4) receptor, which we named h5-HT4(b), h5-HT4(c), and h5-HT4(d). The sequence following the splicing site at Leu358 in the C-terminal tail of h5-HT4(b) displays a 74% protein identity with the same region in the long form of the rat 5-HT4 receptor (r5-HT4L) but is shorter by 18 amino acids compared to its rat counterpart. The splice variants h5-HT4(c) and h5-HT4(d) are the first of their kind to be described in any animal species. The C terminus of h5-HT4(c) displays a high number of putative phosphorylation sites. The h5-HT4(d) isoform corresponds to an ultrashort form of the receptor, with a truncation two amino acids after the splicing site. Tissue distribution studies revealed some degree of specificity in the pattern of expression of the different isoforms within the human body. The four splice variants transiently expressed in COS-7 cells displayed an identical 5-HT4 pharmacological profile and showed a similar ability to stimulate adenylyl cyclase activity in the presence of 5-HT. The stimulatory pattern of cyclic AMP formation in response to the 5-HT4 agonist renzapride was found to be significantly different between h5-HT4(a) and the other h5-HT4 isoforms, indicating that the splice variants may differ in the way they trigger the signal transduction cascade following receptor activation.  相似文献   

3.
4.
The inheritance of anthracnose resistance of the common bean ( Phaseolus vulgaris L.) differential cultivar G 2333 to Colletotrichum lindemuthianum races 73 and 89 was studied in crosses with the susceptible cultivar Rudá. The segregation ratios of 15 : 1 in the F2 and 3 : 1 in the backcrosses to Rudá indicate that for each of the races tested there are two independent resistance loci in G 2333. A random amplified polymorphic DNA (RAPD) molecular marker (OPH181200C) linked in resistance to race 73 was identified in a BC3F2:3 population derived from crosses between Rudá and G 2333. A RAPD molecular marker OPAS13950C, previously identified as linked to gene Co-42 , was also amplified in this population. Co-segregation analyses showed that these two markers are located at 5.6 (OPH181200C) and 11.2 (OPAS13950C) cM of the Co-42 gene. These markers were not present in BC1F2:3 plants resistant to race 89 indicating that this population carries a different resistance gene. DNA amplification of BC1F2:3 plants with RAPD molecular marker OPAB450C, previously identified as linked to gene Co-5 , indicated that this gene is present in this population.  相似文献   

5.
Abstract: Acetylcholinesterase activities and molecular forms were studied in normal and dystrophic 129/ReJ mice, focusing on four predominantly fast-twitch muscles and the slow-twitch soleus. The asymmetric and globular forms were analyzed separately so that the effect of dystrophy on each form could be determined. This comparative study showed the following. (1) In the normal condition, each muscle exhibited a distinct distribution of the molecular forms. (2) The diversity among the fast muscles resulted mainly from variations in the proportions of the three globular forms; in contrast, these muscles showed a constant and precise A12/A8/A4 ratio. (3) The slow-twitch soleus clearly differed from the other muscles in its low acetylcholinesterase activity and distinct distribution of the molecular forms, characterized by a low level of G4 and a peculiar ratio among its asymmetric forms, resulting from a relative increase of the A8 and A4 forms. (4) In dystrophic mice, the diversity of the acetylcholin esterase distribution was lost; all the fast muscles displayed profiles exhibiting the characteristics typical of the soleus. The fast-twitch extensor digitorum longus, sternomastoid, and plantaris converged towards an identical set of acetylcholinesterase molecules. (5) In contrast, the acetylcholinesterase activity and molecular forms of the soleus were only slightly affected by the disease. These results reveal that the dystrophy modifies both categories of molecular forms of acetylcholinesterase in a very precise manner. Such complex changes, which are highly reproducible in a variety of different muscles, are unlikely to result from nonspecific reactions secondary to the disease.  相似文献   

6.
SUMMARY. 1. Sephadex gel filtration of filtered water from small, Finnish forest lakes demonstrated abiotic movement of 33P from added PO4 to two higher molecular weight fractions. This movement was most pronounced in waters with high humic content which also had high iron content. The two fractions which took up 13P had nominal molecular weights of > 100,000 and 10,000-20,000.
2. An equilibrium existed between free PO4 and the two fractions. However, one fraction, at least, appeared to exist in two phases, with one phase in rapid equilibrium with free PO4 but the other in only slow equilibrium.
3. Additions of ferric iron up to 1 mg Fe l−1 to the filtered lake water stimulated movement from free PO4, provided high concentrations of humic materials were present. In the absence of humic materials even 0.1 mg Fe 1−1 would precipitate all added 33PO4.
4. The high molecular weight P was only partially reactive with standard molybdate reagents. Exposure of the high molecular weight P to sunlight caused a small release of PO4 under the experimental conditions employed.
5. Possible implications for biological phosphorus demand of such sequestration of free PO4 by humic materials in combination with iron are discussed.  相似文献   

7.
Abstract. The activity of the green alga Scenedesmus obliquus was studied in simplified nutrient solutions (20 mol m−3 NaNO3, 20 mol m−3 NH4C1, 20 mol m−3 NH4NO3, and 20 mol m−3 NaCl, respectively) at 25 °C. The experiments were performed under welldefined incident photon density fluxes ranging from 10 to 200 μmol m2 s−1, Light-dependent changes in pH and alkalinity (A) were followed by means of a potentiometric method using a glass electrode. In the experiments, carbon dioxide with known partial pressure was bubbled through the algal suspension, and during dark periods ul intervals of 1 h, the solution was allowed to equilibrate with the gas phase. This technique was applied to calculate equilibrium values of pH and alkalinity at regular intervals during a 12-h period. Results obtained in NaNO3, solution show a linear increase in A with time, at each level of illumination studied. After an initial drop, A also increases in NH4NO3, solution in a similar way to that in NaNO3 solution. The change in A with time was also found to increase linearly with the photon density flux studied and no saturation level could be defined. In experiments in NaCl solution, no changes in A were registered while measurements in NH4Cl solution showed a decrease in A with time.  相似文献   

8.
Administration of 17β-oestradiol (E2) to rainbow trout, in the form of hydrogenated coconut oil implants produced a stable, long-term elevation in plasma E2 levels. The elevation was doserelated (over the range 1–10mg kg-1 body weight) both 4 and 8 weeks after implantation. Dose-related increases were also observed with respect to liver weight-body weight ratios and plasma protein levels. Plasma T3 and total calcium levels were depressed and elevated, respectively, by E2 treatment but the responses were not linearly related to the dose of E2 administered; there was no significant effect of E2 on plasma T4 levels.
E2 induced a shift in the binding of T3 to plasma proteins, with T3 binding to smaller molecular weight proteins; neither T4 nor T3 bound to vitellogenin which was present at high levels in the plasma of E2-treated fish.  相似文献   

9.
Abstract: The large majority of the Ca . 150 species of the neotropical shrub and tree genus Clusia have the potential to perform Crassulacean acid metabolism (CAM). They are either obligate CAM plants or C3/CAM intermediate plants. Only a very small percentage of the plants studied so far are apparently obligate C3 species. Among these was C. criuva , until recent laboratory studies showed that it may also have a certain CAM capacity under artificial stress conditions. Measurements of stomatal conductance (porometry) and chlorophyll fluorescence variables of C. criuva occurring along a transect from deep shade inside a gallery forest across the semi-shaded ecotone towards a cerrado and into the exposed cerrado itself in central Brazil now show that it can adapt its photosynthetic apparatus to effective performance of C3 photosynthesis under highly different photosynthetic photon flux densities. In addition, however, it does have a certain potential for CAM and cannot be considered as a strictly obligate C3 plant. Should a basic capacity for performing CAM be a general property of the genus, the quest for CAM traits in other remaining putatively obligate C3 species of the genus ought to be pursued.  相似文献   

10.
Abstract: Using a whole-cell binding procedure with long incubations at low temperature and subsequent acid stripping, we have characterized an atypical endothelin (ET) receptor in primary rat cortical astrocyte cultures. We found the following: (a) no competition for 125I-ET-1 binding by the ETA antagonists BQ-123 and LU 135252 or the ETB agonist IRL 1620; (b) weak competition by the ETB antagonist BQ-788 and by the predominant ETB ligand ET-3; (c) potent synergistic competition of ETA and ETB ligands in combination for 125I-ET-1 binding; (d) potent competition of ET-1 with any of the radioligands used, 125I-ET-1, 125I-IRL 1620, and [3H]BQ-123; (e) lack of competition of IRL 1620 and BQ-123 with the respective other radioligand; (f) shifting of the amount of acid-strippable 125I-ET-1 binding from 20 to 80% by ETB ligands and to 4% by ETA ligands; and (g) as a control, typical ETA and ETB binding characteristics of the RAT-1 fibroblast and the U373MG astrocytoma cell line, respectively, under our assay conditions. The unusual binding properties of astrocytic ET receptors described in this study appear to be the result of several binding sites in the receptor for different ET ligands or ligand epitopes.  相似文献   

11.
N 5 N 10-Methylenetetrahydromethanopterin reductase was purified 13-fold to apparent homogeneity from methanol grown Methanosarcina barkeri . The colourless enzyme was found to be composed of four identical subunits of apparent molecular mass 36 kDa. It catalysed the reduction of methylenetetrahydromethanopterin ( K m=15 μM) to methyltetrahydromethanopterin with reduced coenzyme F420 ( K m=12 μM) at a specific rate ( V max) of 2200 μmol min−1· mg protein−1 ( K cat=1320 s−1). With respect to coenzyme specificity, molecular properties and catalytic mechanism the enzyme was found to be similar to CH2=H4MPT reductase of Methanobacterium thermoautotrophicum which phylogenetically is only distantly related to M. barkeri .  相似文献   

12.
Abstract: Over 60 Salsola species of Chenopodiaceae from South Africa were studied for their photosynthesis type, using δ13C analysis and light microscopy of leaf anatomy. These species cover about 70 % of the total list of Southern African Salsola species and grow naturally in South and Southwest African desert regions. All species are shrubby forms and belong to the single subsection Caroxylon. Only C4 photosynthesis was found in the Salsola species determined with 13C/12C carbon isotope discrimination values that ranged from - 11.04 to - 14.03 % (PDB), plus the presence of a Kranz type assimilation tissue anatomy. The apparent absence of C3 in Salsola in South and Southwest Africa and the known presence of C3 and C3 - C4 intermediate photosynthesis in Caroxylon, Salsola species in Asia strongly indicate that the genus Salsola originated in Asia and later migrated to South Africa.  相似文献   

13.
Abstract: The 7315c pituitary tumor cell expresses a homogeneous population of dopamine receptors that are functionally similar to brain dopamine D2 receptors. [3H]-Sulpiride binding to 7315c cell homogenates was specific and saturable, and K i values for compounds to compete for these sites were highly correlated with values for the same compounds at D2 receptors in brain. Dopamine maximally inhibited ∼65% of forskolin-stimulated cyclase activity in cell membranes. Some D2 agonists had lower efficacies, suggesting that some compounds are partial agonists at this receptor. Removal of GTP from the assay buffer or pretreatment of the tissue with pertussis toxin abolished the inhibition of adenylyl cyclase by dopamine. Immunodetection of most of the known Gα subunits revealed that Gi1, Gi2, Gi3, Go, Gq, and Gs are present in the 7315c membrane. Pretreatment with the AS antibody (which recognizes the C-terminal regions of Gαi1 and Gαi2) significantly attenuated the inhibition of adenylyl cyclase activity by dopamine, whereas antibodies to C-terminal regions of the other Gα subunits had no effect. These findings suggest that the dopamine D2 receptor regulates cyclase inhibition predominantly via Gi1 and/or Gi2 and that the 7315c tumor cells provide a useful model for studying naturally expressed dopamine D2 receptors in the absence of other dopamine receptor subtypes.  相似文献   

14.
Abstract— In in vitro experiments on rat hypothalamic homogenates the effects of biogenic amines such as histamine (HA), noradrenaline (NA), dopamine (DA), serotonin (5-HT) and drugs such as isoprenaline (ISP), 2-(2-pyridyl)ethylamine (H2 stimulant—Hls), 4-methyl-histamine (H2 stimulant H2s), mepyramine (H1 antagonistp Hla), cimetidine (H2 antagonist—H2a) were tested on adenylate cyclase activity. HA possessed a powerful stimulating effect on hypothalamic adenylate cyclase activity, higher than that shown by the other substances.
The stimulating effect of HA was greatest in hypothalamic tissue from male rats, while tissue from females showed only a modest stimulation. H2s, induced a greater stimulation of adenylate cyclase than Hls. On the other hand, the H2a inhibited HA stimulation to a greater extent than the Hla, Hla and H2a, when used together, completely inhibited the HA stimulation. HA may have a neurotrans-mitter role in the hypothalamus, and in this area there appears to be a mixed population of H1 and H2 receptors, with a majority of H2 receptors.  相似文献   

15.
Gibberellin biosynthesis pathways were investigated using isotopically-labelled C19- and C20-gibberellins and cell-free preparations from immature seed of Phaseous coccineus cv. Prizewinner. The initial steps in an early 13-hydroxylation pathway involved the conversion gibberellin A12-aldehyde (GA12-aldehyde) to GA12 which was 13-hydroxylated to yield GA53, Metabolism of GA53 yielded GA44. In contrast to other cell-free systems, GA44 was not further converted, either as a δ-lactone or an open-lactone structure, to the C-20 aldehyde GA19. GA19 was, however, metabolised to GA20, GA5 and GA1. GA20 represented a branch point in the pathway as it was converted both to GA1, which was an end product, and GA5 which was further converted to GA6. Like GA1, GA6 was also an end-product of the early 13-hydroxylation pathway.
A non-13-hydroxylation pathway involving GA4, GA15, GA24 GA37 and GA36 also originated from GA12. The terminal product of this pathway was the 3β-hydroxy C19-gibberellin, GA4.  相似文献   

16.
Relationship between photosystem II activity and CO2 fixation in leaves   总被引:9,自引:2,他引:7  
There is now potential to estimate photosystem II (PSII) activity in vivo from chlorophyll fluorescence measurements and thus gauge PSII activity per CO2 fixed. A measure of the quantum yield of photosystem II, ΦII (electron/photon absorbed by PSII), can be obtained in leaves under steady-state conditions in the light using a modulated fluorescence system. The rate of electron transport from PSII equals ΦII times incident light intensity times the fraction of incident light absorbed by PSII. In C4 plants, there is a linear relationship between PSII activity and CO2 fixation, since there are no other major sinks for electrons; thus measurements of quantum yield of PSII may be used to estimate rates of photosynthesis in C4 species. In C3 plants, both CO2 fixation and photorespiration are major sinks for electrons from PSII (a minimum of 4 electrons are required per CO2, or per O2 reacting with RuBP). The rates of PSII activity associated with photosynthesis in C3 plants, based on estimates of the rates of carboxylation (vo) and oxygenation (vo) at various levels of CO2 and O2, largely account for the PSII activity determined from fluorescence measurements. Thus, in C3 plants, the partitioning of electron flow between photosynthesis and photorespiration can be evaluated from analysis of fluorescence and CO2 fixation.  相似文献   

17.
Abstract: Coated vesicles (CVs) isolated from bovine striatal tissue were examined to determine whether they are associated with dopamine signal systems consisting of dopamine D1 and D2 receptors, G proteins, and adenylate cyclase. Dopamine receptors in CVs were characterized by a dopamine D1 receptor antagonist, [3H]SCH 23390, and a dopamine D2 receptor antagonist, [3H]-spiroperidol. The bindings of both ligands were specifically saturable and reversible with a dissociation constant ( K D) of 0.65 and 0.5 n M , respectively. Dopaminergic antagonists and agonists inhibited the specific bindings of [3H]SCH 23390 and [3H]spiroperidol in a stereoselective and concentration-dependent manner with an appropriate rank order potency for dopamine D1 or D2 receptors. The regulations of the agonist binding by guanyl-5-ylimidodiphosphate were observed. ADP ribosylation of the CVs with [32P]NAD demonstrated predominant labeling of bands of Mr 47,000–52,000, 42,000–45,000, and 40,000-39,000, which corresponded to the known molecular weights of the α subunits of Gs and Gi proteins. The presence of α and β subunits of G proteins in the CVs was also confirmed by immunoblotting assay. Adenylate cyclase activity, which was stimulated by SKF 38393 and inhibited by dopamine D2 receptor agonists, was present in the CVs. These findings suggest that the dopamine D1 and D2 receptors in the CVs couple with adenylate cyclase via Gs/Gi protein.  相似文献   

18.
Abstract Bradyrhizobium japonicum and Shewanella putrefaciens were unable to oxidize hydrogen at atmospheric concentrations (0.55 ppmv), neither in suspension nor when added to sterile soil. The K m-value of S. putrefaciens for H2 (39 ppmv in gas phase, 0.22 μM in aqueous phase), using Fe(III) as electron acceptor, showed a 4–5-fold higher affinity for H2 than that of B. japonicum (1200 ppmv; 0.84 μM) or other hydrogen-oxidizing bacteria. However, the V max (4.54 fmol H2 h−1 cell −1) and threshold (> 0.5 ppmv; 0.35 nM) of S. putrefaciens and the V max (7.19 fmol H2 h−1 cell−1) and threshold (> 0.5 ppmv; 0.35 nM) of B. japonicum were in the same order of magnitude as data for Knallgas bacteria from relevant literature. To enable hydrogen oxidation in soil the soil-samples with S. putrefaciens even had to be supplemented with Fe(III). Fresh soil, on the other hand, oxidized hydrogen very efficiently below atmospheric mixing ratios, demonstrating that there must be other oxidation activities in soil.  相似文献   

19.
A protease-sensitive antibacterial substance produced by Bacillus coagulans I4 strain, isolated from cattle faeces, was classified as a bacteriocin-like inhibitory substance and named coagulin. The inhibitory spectrum included B. coagulans and unrelated bacteria such as Enterococcus , Leuconostoc , Oenococcus , Listeria and Pediococcus . Coagulin was stable at 60 °C for 90 min, at a pH ranging from 4 to 8 and appeared to be unaffected by α-amylase, lipase or organic solvents (10% v/v). Coagulin exhibited a bactericidal and a bacteriolytic mode of action against indicator cells. The apparent molecular mass was estimated to be about 3–4 kDa by SDS-PAGE. The B. coagulans I4 strain harbours a plasmid, pI4, approximately 14 kb in size. Novobiocin curing experiments yielded two derivatives that no longer produced the bacteriocin-like inhibitory substance. Plasmid content of these two derivatives showed that one had lost pI4,whereas the second harboured a deleted form of this plasmid, thus suggesting a plasmid location for the genes for coagulin production.  相似文献   

20.
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