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44.
Species-specific algal responses to zooplankton: experimental and field observations in three nutrient-limited lakes 总被引:3,自引:0,他引:3
Elser James J.; Goff Nancy C.; MacKay Neil A.; Amand Ann L.St.; Elser Monica M.; Carpenter Stephen R. 《Journal of plankton research》1987,9(4):699-717
A series of 4-day manipulations of zooplankton biomass and nutrientavailability was performed in enclosures in three lakes to determinespecies-specific algal responses to herbivory and nutrient enrichment.Algal performance in enclosures was compared to the relationshipsbetween weekly algal growth rates and the zooplankton in situ.When in situ growth rates were significant functions of zooplanktonbiomass, the responses were generally consistent with responsesin the enclosure experiments. The importance of both nutrientsand zooplankton in mediating algal growth was demonstrated bynumerous observations: strong algal community response to enrichment,unimodal or positive responses of certain algal taxa to zooplanktonbiomass, differences in degree of nutrient limitation amongthe algal response types, lack of nutrient limitation of non-grazedalgal taxa and a preponderance of taxa with no net responseto increasing zooplankton biomass. Variation in the zooplanktoncommunity may be the largest source of variability in nutrientsupply rate during summer in stratified lakes, and causes substationalvariability in the algae. Algae responded more strongly to changesin zooplankton composition than to changes in zooplankton biomass.We conclude that, due to the close coupling of phytoplanktonand zooplankton communities in these nutrient-limited lakes,major compositional changes in the zooplankton have greatereffects on the algae than do changes in biomass of grazers alreadypresent.
1Present address: Division of Environmental Studies, Universityof California, Davis, CA 95616, USA
2Present address: Division of Biological Sciences, Universityof California, Davis, CA 95616, USA 相似文献
45.
Calcium-Dependent Release of Tyrosine in Brain Elicited by Stimulation of Neuropeptide Receptors 总被引:1,自引:1,他引:0
We sought to establish whether the endogenous opiate-receptor agonist Met-enkephalin (m-ENK) selectively modulates the release of endogenous tyrosine (Tyr) from brain slices prepared from the corpus striatum (CS). Amino acids (AAs) released from slices of CS and, for comparison, cerebral cortex (Cx) were measured by HPLC. Incubation of slices with m-ENK (1-10 microM) increased the basal release of Tyr (up to 293% of control) from CS, but not Cx, whereas other nonneurotransmitter AAs, phenylalanine (Phe) and valine (Val), were unchanged. The release of the putative neurotransmitter AAs glutamate (Glu), taurine (Tau), and glycine (Gly) were similarly increased by 50-150% with m-ENK in slices of CS, but not Cx. The enhanced release of AAs by m-ENK was prevented by removal of extracellular Ca2+ or by preincubation with the opiate receptor antagonist naloxone. Neuronal depolarization by potassium (5-55 mM) in the presence of Ca2+ did not affect the release of Tyr, whereas release of neurotransmitter AAs such as gamma-aminobutyric acid (GABA) were markedly increased. The increase in basal Tyr release by m-ENK was not the result of a decreased uptake of Tyr. Relative to slices, the basal release of Tyr, Phe, and Val from a synaptosomal (P2) preparation of CS was small (8-51%) compared to that of GABA, Gly, Glu, and Tau (49-123%). Nonetheless, m-ENK (10 microM) markedly increased the release of Tyr (to 833%), but not Glu, Gly, and Tau from the P2 fraction.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
46.
Use of permeabilised cells of Chara corallina provides a uniqueopportunity to study the electrical characteristics of the tonoplastwhilst being able to control ionic conditions on the outsideof the membrane. Current-voltage (I/V) analysis over wide voltagespans, and admittance measurements at 5 Hz showed that manypermeabilised cells had a similar conductance and capacitanceto the tonoplast of intact cells. Cells developed two regionsof negative-slope conductance upon addition of external Cl,which suggests the existence of potential-dependent Clchannels in the Chara tonoplast. With Cl concentrationssimilar to those expected in vivo, the resting potential wasmore sensitive to changes in external K+ than Cl; however,a decrease in external K+ did not significantly alter the shapeof the I/V relation.
1Present address: Biopysics Laboratory, School of BiologicalSciences, A12, University of Sydney, Sydney, N.S.W., 2006, Australia
2Permanent address: Department of botany, Faculty of Science,University of Tokyo, Hongo, Tokyo 113, Japan (Received May 6, 1987; Accepted September 21, 1987) 相似文献
47.
Characterisation of a new monoclonal antibody (mAb), designated LAS 41, directed against 124-kilodalton (kDa) etiolated-oat (Avena sativa L.) phytochrome, indicates that it recognises an epitope unique to the red-light-absorbing form, Pr. In a solid-phase enzyme-linked immunosorbent assay (ELISA), LAS 41 exhibits a seven- to eight-fold higher affinity for Pr than for the far-red-light-absorbing form of phytochrome, Pfr. In addition, in immunoprecipitation assays LAS 41 effectively precipitates 100% of phytochrome presented as Pr but only precipitates a maximum of 24.5% of phytochrome presented as Pfr. These values are indicative of binding exclusively to Pr. Peptide-mapping studies show that LAS 41 recognises and epitope located within a region 6–10 kDa from the aminoterminus of the phytochrome molecule. Since binding of LAS 41 to Pr induces alterations in the spectral properties of Pr, this indicates that at least part of the 4 kDa domain to which the antibody binds is essential for protein-chromophore interaction. Subsequent photoconversion of LAS 41-Pr complexes produces native Pfr spectra, with concomitant production of free antibody and antigen, as shown by a modified ELISA. The specificity of LAS 41 for Pr has facilitated the purification of Pfr which is free of contaminating Pr. This has enabled direct determination of the mole fraction of Pfr established by red light to be 0.874.Abbreviations ELISA
enzyme-linked immunsorbent assay
- kDa
kilodalton
- mAb
monoclonal antibody
- Pfr
far-red-absorbing form of phytochrome
- Pr
red-absorbing form of phytochrome
- SDS-PAGE
sodium dodecyl sulphate polyacrylamide gel electrophoresis
- (A)
difference in absorbance (A
665
Pr
–A
730
Pr
)-(A
665
Pfr
–A
730
Pfr
)
- Ar/Afr
spectral change ratio (SCR)
- max
mole fraction of Pfr following saturating red light 相似文献
48.
We found that extensive metabolic switching can be triggered in aromatization. Up to 20–35% of (19-3H3)-labeled substrate is diverted to non-estrogenic product, namely 1β- and 2β-hydroxy androgens, negating usefulness for [3H]water assays. The strikingly substrate-specific metabolite patterns observed reflect positioning at the active site, and the large kinetic isotope effects involved. This switching is unusual in that it involves: 1) tritium labeling, 2) a multistep enzymic process, and 3) the potential unraveling of an enzymic mechanism. 相似文献
49.
Stanley A. Vinores Mary M. Herman Lucien J. Rubinstein 《The Histochemical journal》1987,19(8):439-448
Summary Neuron-specific () enolase, a glycolytic enzyme used as a relatively specific marker for normal neurons and neuroendocrine cells, has recently been found in a variety of neoplastic cells and in reactive astrocytes. Its localization was investigated by immunohisto- and electron-immunocyto-chemistry, in the proliferating supportive Schwann cells of a peripheral ganglioneuroblastoma and in the neoplastic Schwann cells of four acoustic tumours. By light microscopy, the neoplastic Schwann cells showed moderate uneven diffuse immunopositivity for enolase. By electron-immunocy-tochemistry, both types of Schwann cells demonstrated immunopositivity discretely limited to their cell surface membranes. The neoplastic ganglion cells and axons of the ganglioneuroblastoma and the normal neurons and axons included in the schwannomas were, as expected, intensely immunopositive. The visualization of enolase on the cell surface membranes of both neoplastic and non-neoplastic proliferating Schwann cells suggests that increased glycolytic activity may occur on the surface of these proliferating cells irrespective of the nature of the proliferation. 相似文献
50.
Ann Bucklin 《Journal of experimental marine biology and ecology》1987,110(3):225-243
Individual size, rate of growth, and mode and frequency of asexual reproduction are life-history traits of primary importance for sea anemones. These traits determine sexual reproductive output, affect an individual's probability of survival, and are crucial in adapting an individual to its environmental surroundings. The sea anemone Metridium senile (L.) is highly variable in ecological distribution and life history, including rate of growth, individual size, and rate of asexual reproduction. Gonad size (measured as cross-sectional area of gonadal tissue) increases with body weight, so individuals should grow as large and as rapidly as possible to maximize individual sexual reproductive output. Cessation of growth and small body size in intertidal populations suggest that growth is constrained by genetic or environmental conditions. The growth of intertidal individuals transplanted to harbor-float panels demonstrated that growth limits are imposed by environmental factors, most probably limited food and feeding time and damage from wave exposure (which stimulates fragmentation). Individuals in harbor-float populations, which are continuously immersed, grow much larger, and large individuals comprise a greater proportion of the population than in the intertidal zone. The highest rate of fragmentation observed was on harbor-float panels. Patterns of growth and asexual reproduction provide adaptive advantages for M. senile. For harborfloat individuals, large individual size increases gamete production and may increase feeding efficiency. For intertidal individuals, asexual reproduction allows growth despite individual size constraints and rapid population growth, with specific advantages resulting from clone formation. 相似文献