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221.
Rooted cuttings ofCeanothus griseus varhorizontalis were irrigated with 0, 10, 20, 50, 75 or 100ppm nitrogen as NH4NO3 for eight weeks prior to inoculation with infectiveFrankia. After inoculation, half of the plants for each treatment nitrogen level continued to be irrigated with the preconditioning nitrogen level and half were given no more supplemental nitrogen. For plants continuously receiving nitrogen, nodule initiation (nodule number) was inversely correlated with increasing supplemental nitrogen levels, and suppressed above 50 ppm N. Leaf nitrogen above 2% in continuous-N plants correlated with greatly reduced or suppressed nodulation. Plants maintained after inoculation without supplemental nitrogen showed influence of the prior nitrogen treatment on nodulation. Preconditioning at 50 ppm and above greatly reduced the number of nodules formed. The evidence suggests that stored internal nitrogen can regulate nodulation.Plant biomass accumulated maximally when nodulation was suppressed, at 75 and 100 ppm supplemental N applied continuously. Internode elongation during the nodulation period occurred only on nodulated plants, or in the presence of supplemental N (10 ppm and above). 相似文献
222.
The STE4 and STE18 genes of yeast encode potential beta and gamma subunits of the mating factor receptor-coupled G protein 总被引:85,自引:0,他引:85
M Whiteway L Hougan D Dignard D Y Thomas L Bell G C Saari F J Grant P O'Hara V L MacKay 《Cell》1989,56(3):467-477
The STE4 and STE18 genes are required for haploid yeast cell mating. Sequencing of the cloned genes revealed that the STE4 polypeptide shows extensive homology to the beta subunits of mammalian G proteins, while the STE18 polypeptide shows weak similarity to the gamma subunit of transducin. Null mutations in either gene can suppress the haploid-specific cell-cycle arrest caused by mutations in the SCG1 gene (previously shown to encode a protein with similarity to the alpha subunit of G proteins). We propose that the products of the STE4 and STE18 genes comprise the beta and gamma subunits of a G protein complex coupled to the mating pheromone receptors. The genetic data suggest pheromone-receptor binding leads to the dissociation of the alpha subunit from beta gamma (as shown for mammalian G proteins), and the free beta gamma element initiates the pheromone response. 相似文献
223.
Heinz W. Kunz Andrea L. Cortese Hassett Tetsuo Inomata D. N. Misra Thomas J. Gill III 《Immunogenetics》1989,30(3):181-187
A new antigenic system in the rat homologous to theQa/TL antigen system in the mouse has been characterized. It was detected by antibodies raised in donor-recipient combinations
that were matched for theRT1. A, B, D, E loci in the major histocompatibility complex (MHC): (R11×BN)F1 anti-BN.1L(LEW), (R18×BN)F1 anti-BN.1L, and BN.1LV1(F344) anti-BN.1L. Absorption analyses using these antisera and a variety of inbred, congenic and
recombinant strains identified three alleles,RT1.G
a
,G
b
,G
c
, of whichG
c
is a null allele. The strain distribution of these alleles was determined, using 37 strains of rats representative of all
of the prototypic haplotypes and a number of congenic and recombinant strains. The use of the congenic and recombinant strains
showed that theRT1.G locus was linked to the MHC and that the most probable gene order wasA-E-G. Testcross analysis showed that the map distance betweenA andG was 1.4 cM(4/285 recombinants). The RT1.G antigen has a heavy chain ofM
r 46 000 and is present on both T and B cells. 相似文献
224.
The role of ciliated protozoa in pelagic freshwater ecosystems 总被引:11,自引:0,他引:11
The abundance and biomass of ciliates are both strongly related to lake trophic status as measured by chlorophylla concentrations. Taxonomic replacements occur with increasing eutrophication such that large-bodied forms (predominantly oligotrichs) are progressively replaced by smaller-bodied ciliates (mainly scuticociliates). Highly acidic lakes display a more pronounced dominance of large-bodied forms when contrasted with less acidic lakes of comparable trophy. Community structure of ciliate populations is determined largely by lake trophy with acidic oligotrophic systems being characterized by reduced diversity and species richness compared with hypereutrophic systems. The temporal and spatial distribution of small (< 100m) ciliate populations is ascribed to lake thermal regimes which provide localized concentrations of food resources. Likewise, in extremely productive lakes, very large (> 100m) meroplanktonic ciliates enter the water column during midsummer after the development of thermal stratification and associated profundal deoxygenation. Laboratory studies indicate that large zooplankton (crustaceans) are capable of utilizing ciliates as a food source, but there is little direct evidence from field studies documenting this trophic link. Ciliates can be voracious grazers of both bacterioplankton and phytoplankton, and each species has a distinct range of preferred particle size which is a function of both mouth size and morphology. Myxotrophic ciliates may be important components in some plankton communities, particularly during periods of nutrient limitation or after their displacement from the benthos of eutrophic lakes. Evidence regarding the importance of planktonic ciliated protozoa in nutrient regeneration and as intermediaries in energy flow is discussed. 相似文献
225.
Biochemical studies of soluble atrial natriuretic peptide (ANP) receptors from rat olfactory bulb and vascular smooth muscle cells 总被引:1,自引:0,他引:1
Christopher C. Glembotski Gary M. Wildey Thomas R. Gibson 《Cellular and molecular neurobiology》1989,9(1):57-73
1. Aim. The biochemical characteristics of atrial natriuretic peptide receptors (ANP-R) derived from rat vascular smooth muscle (A-10 cell line) and central nervous system (CNS; olfactory bulb) tissue were compared. 2. Method and Results. ANP-Rs from each source were solubilized with 40 to 65% efficiency utilizing the nonionic detergent Lubrol-PX. Upon solubilization, the ANP-R from each source maintained the ability to bind 125I-ANP (99-126) with a high affinity; Scatchard analysis indicated that the VSMC ANP-R displayed a Kd for the radioligand of approximately 10 pM, whereas the olfactory receptor possessed a Kd of about 165 pM. The Bmax values for the soluble VSMC and olfactory ANP-Rs were 285 and 30 fmol/mg protein, respectively. Competition binding studies indicated that the VSMC ANP-R bound ANP(99-126), ANP(103-126), and ANP(103-123) with similar affinities, whereas the olfactory ANP-R was much more sensitive to changes in the COOH-terminal structure of the competing peptide. The soluble ANP-Rs from VSMC and olfactory were chromatographically indistinguishable on phenyl-, DEAE-, and wheat germ agglutinin-agarose columns. However, the ANP-Rs could be distinguished using GTP-agarose; the olfactory ANP-R was capable of binding to the resin, whereas the VSMC ANP-R was not. 3. Conclusions. Coupled with other studies, these data suggest that the A10 VSMC ANP-R observed in this study may not be coupled to guanylate cyclase and may represent a receptor serving a clearance function, whereas a significant proportion of the olfactory CNS ANP-R appears to be associated with GTP-binding proteins, likely particulate guanylate cyclase, and probably represents a coupled form of the receptor. 相似文献
226.
227.
Filter types, filtration and post-filtration treatment in phytoplankton production studies 总被引:1,自引:0,他引:1
Acid rinsing, used to decontaminate filters in 14C productionstudies, caused cell rupture and resulted in elevated 14C countsin the filtrates of six out of seven phytoplankton samples.Large volume (50 ml) rinses using only water caused some, butlesser, damage. Comparing the recovery of 14C-labelled cellsand chlorophyll a on glass-fibre, polycarbonate and celluloseester filters revealed unaccountable losses at times with allthree filter types. These losses could not be explained by cellrupture, attachment to the filter funnel wall, filter treatmentor self-absorption during scintillation counting. Compared tothe whole sample acid bubbling method, recovery on the glass-fibrefilters was highest. Results for the polycarbonate filters weremore variable, while, in all cases, recovery on cellulose esterfilters was much lower. 相似文献
228.
Tudor H. Thomas 《Plant Growth Regulation》1989,8(3):255-261
The temperature-dependent, primary dormancy of cv. Florida 683 celery seeds in darkness was partially broken by a 30 min light exposure on the third day of incubation at 20–22°C, resulting in c 50 percent germination after 20 days. This light stimulation was negated by including different inhibitors of gibberellin biosynthesis in the incubation medium. Subsequent addition of a solution of the gibberellins A4 and A7 or of the gibberellin-active compound (1-3-chlorophthalimido)-cyclohexane carboxamide (AC94,377) overcame the inhibitory effects on germination of these GA-biosynthesis inhibitors. It is suggested that light stimulates the biosynthesis of gibberellins which are essential for dormancy-break in celery seeds and that this biosynthesis is either directly or indirectly controlled through phytochrome.Abbreviations AC94,377
1-(3-chlorophthalimido)-cyclohexane carboxamide; ancymidol, -cyclopropyl--(4-methoxyphenyl)-5-pyrimidinemethanol
- AMO1618
N,N,N-2-tetramethyl-5-(1-methyl ethyl)-4-(1-piperidinylcarbonyl)oxy-benzenaminium chloride
- BTS44584
S-2,5-dimethyl-4-pentamethylenecarbamoyloxyphenyl-SS-dimethyl sulphonium
- P
toluenesulphonate; chlormequat chloride, 2-chloroethyltrimethylammonium chloride; daminozide
- N
dimethylaminoscuccinamic acid; paclobutrazol, (2RS, 3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl pentan-3-ol) 相似文献
229.
230.
Thomas A. Churchill Kenneth B. Storey 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1989,159(4):461-472
Summary The course of glycerol biosynthesis, initiated by exposure to –4°C, was monitored in larvae of the goldenrod gall moth,Epiblema scudderiana, and accompanying changes in the levels of intermediates of glycolysis, adenylates, glycogen, glucose, fructose-2,6-bisphosphate, and fermentative end products were characterized. Production of cryoprotectant was initiated within 6 h after a switch from +16° to –4°C, with halfmaximal levels reached in 30 h and maximal content, 450–500 mol/g wet weight, achieved after 4 days. Changes in the levels of intermediates of the synthetic pathway within 2 h at –4°C indicated that the regulatory sites involved glycogen phosphorylase, phosphofructokinase, and glycerol-3-phosphatase. A rapid increase in fructose-2,6-bisphosphate, an activator of phosphofructokinase and inhibitor of fructose-1,6-bisphosphatase, appeared to have a role in maintaining flux in the direction of glycerol biosynthesis. Analysis of metabolite changes as glycerol production slowed suggested that the inhibitory restriction of the regulatory enzymes was slightly out of phase. Inhibition at the glycerol-3-phosphatase locus apparently occurred first and resulted in a build-up of glycolytic intermediates and an overflow accumulation of glucose. Glucose inhibition of phosphorylase, stimulating the conversion of the activea to the inactiveb forms, appears to be the mechanism that shuts off phosphorylase function, counteracting the effects of low temperature that are the basis of the initial enzyme activation. Equivalent experiments carried out under a nitrogen gas atmosphere suggested that the metabolic make-up of the larvae in autumn is one that obligately routes carbohydrate flux through the hexose monophosphate shunt. The consequence of this is that fermentative ATP production during anoxia is linked to the accumulation of large amounts of glycerol as the only means of maintaining redox balance.Abbreviations
G6P
glucose-6-phosphate
-
F6P
fructose-6-phosphate
-
F1, 6P
fructose-1,6-bisphosphate
-
F2,6P
2
fructose-2,6-bisphosphate
-
G3P
grycerol-3-phosphate
-
DHAP
dinydroxyacetonephosphate
-
GAP
glyceraldehyde-3-phosphate
-
PEP
phosphoenolpyruvate
-
PFK
phosphofructokinase
-
FBPase
fructose-1,6-bisphosphatase
-
PK
pyruvate kinase 相似文献