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1.
2.
A Model for the Regulation of K Influx, and Tissue Potassium Concentrations by Negative Feedback Effects upon Plasmalemma Influx 总被引:1,自引:0,他引:1
By means of a modified Michaelis-Menten equation for K+ influx, which includes terms for root and external K+ concentrations (root [K+] and [K+]0, respectively) it is possible to predict the manner in which short-term (perturbation) fluxes of K+ into roots of barley plants (Hordeum vulgare cv Fergus) vary with root [K+] and [K+]0. Influx values derived from this equation were used to predict changes of root and shoot [K+] and K+ absorption rates (as functions of time and [K+]0) from a knowledge of K+ efflux, relative growth rates of roots and shoots, and the partitioning of absorbed K+ between these organs. A microcomputer program was employed to model these changes in low-salt plants following transfer to solutions in which [K+]0 was maintained at values ranging from 5 to 1000 millimoles per cubic meter. The model was operated on the basis of 10 minute absorption periods which provided data for continuous `updating' of tissue [K+]. The simulations were undertaken for periods corresponding to 30 days. During this time the model accurately predicted the manner in which K+ influx and root and shoot [K+] gradually approach values which are essentially independent of [K+]0. The computer program was also used to predict the outcome of changing various external and internal parameters of the proposed regulatory system. The results of these simulations are discussed in the context of current models for negative feedback control of ion fluxes. 相似文献
3.
Time-Dependent Increase in Protein Phosphorylation Following One-Trial Enhancement in Hermissenda 总被引:1,自引:1,他引:0
Abstract: One-trial conditioning of the nudibranch mollusk Hermissenda produces short- and long-term changes in excitability (enhancement) of identified sensory neurons. To investigate the biochemical mechanisms underlying this example of plasticity, we have examined changes in protein phosphorylation at different times following the in vitro conditioning trial. Changes in the incorporation of 32 PO4 into proteins were determined using two-dimensional polyacrylamide gel electrophoresis, autoradiography, and densitometry. Conditioning resulted in increases in levels of several phosphoproteins, five of which, ranging in apparent molecular mass from 22 to 55 kDa, were chosen for analysis. The increased phosphorylation of the 46- and 55-kDa phosphoproteins detected 2 h postconditioning was significantly greater than the level of phosphorylation detected in an unpaired control group, indicating that long-term enhancement is pairing specific. Statistically significant increases in phosphorylation as compared with the control group that received only light were detected immediately after conditioning (5 min) for the 55-, 46-, and 22-kDa phosphoproteins, at 1 h for the 55- and 46-kDa phosphoproteins, and at 2 h for the 55-, 46-, and 22-kDa phosphoproteins. The 46- and 55-kDa phosphoproteins are putative structural proteins, and the 22-kDa phosphoprotein is proposed to be a protein kinase C substrate previously identified in Hermissenda following multitrial classical conditioning. Time-dependent increases in protein phosphorylation may contribute to the induction and maintenance of different memory stages expressed in sensory neurons after one-trial conditioning. 相似文献
4.
5.
Anonymous nuclear DNA markers in the American oyster and their implications for the heterozygote deficiency phenomenon in marine bivalves 总被引:4,自引:0,他引:4
A puzzling population-genetic phenomenon widely reported in allozyme
surveys of marine bivalves is the occurrence of heterozygote deficits
relative to Hardy-Weinberg expectations. Possible explanations for this
pattern are categorized with respect to whether the effects should be
confined to protein-level assays or are genomically pervasive and expected
to be registered in both protein- and DNA-level assays. Anonymous nuclear
DNA markers from the American oyster were employed to reexamine the
phenomenon. In assays based on the polymerase chain reaction (PCR), two
DNA-level processes were encountered that can lead to artifactual genotypic
scorings: (a) differential amplification of alleles at a target locus and
(b) amplification from multiple paralogous loci. We describe symptoms of
these complications and prescribe methods that should generally help to
ameliorate them. When artifactual scorings at two anonymous DNA loci in the
American oyster were corrected, Hardy-Weinberg deviations registered in
preliminary population assays decreased to nonsignificant values.
Implications of these findings for the heterozygote-deficit phenomenon in
marine bivalves, and for the general development and use of PCR-based
assays, are discussed.
相似文献
6.
The Effects of Aluminum on the Influx of Calcium,Potassium, Ammonium,Nitrate, and Phosphate in an Aluminum-Sensitive Cultivar of Barley (Hordeum vulgare L.) 总被引:6,自引:4,他引:2 下载免费PDF全文
The mechanism by which aluminum interferes with ion influx is not known. In this study, the effects of aluminum on the influx of the cations calcium, potassium, and ammonium and the anions nitrate and phosphate were measured in an aluminum-sensitive cultivar of barley (Hordeum vulgare L.). Aluminum (100 [mu]M) was found to inhibit the influx of the cations calcium (69%), ammonium (40%), and potassium (13%) and enhancing the influx of the anions nitrate (44%) and phosphate (17%). Aluminum interfered with the binding of the cations in the cell wall by the same order of magnitude as their respective influxes, whereas phosphate binding was strongly enhanced. The results are consistent with a mechanism whereby aluminum binds to the plasma membrane phospholipids, forming a positively charged layer that influences ion movement to the binding sites of the transport proteins. A positive charge layer would retard the movement of cations and increase the movement of anions to the plasma membrane in proportion to the charges carried by these ions. 相似文献
7.
Compartmentation and flux characteristics of nitrate in spruce 总被引:8,自引:0,他引:8
The radiotracer13N was used to undertake compartmental analyses for NO
3
–
in intact non-mycorrhizal roots ofPicea glauca (Moench) Voss. seedlings. Three compartments were defined, with half-lives of exchange of 2.5 s, 20 s, and 7 min. These were identified as representing surface adsorption, apparent free space, and cytoplasm, respectively. Influx, efflux, and net flux as well as cytoplasmic and apparent-free-space nitrate concentrations were estimated for three different concentration regimes of external nitrate. After exposure to external NO
3
–
for 3 d, influx was calculated to be 0.09 mol·g–1·h–1 (at 10 M [NO
3
–
]o), 0.5mol·g–1·h–1 (at 100 M [NO
inf3
sup–
]o), and 1.2 mol · g–1· h–1 (at 1.5 mM [NO
3
–
]o). Efflux increased with increasing [NO
3
–
]o, constituting 4% of influx at 10 M, 6% at 100 M, and 21% at 1.5 mM. Cytoplasmic [NO
3
–
] was estimated to be 0.3 mM at 10 uM [NO
3
–
]o, 2mM at 100 M [NO
3
–
]o, and 4mM at 1.5 mM [NO
3
–
]o, while free-space [NO
3
–
] was 16 M, 173 M, and 2.2 mM, respectively. A series of experiments was carried out to confirm the identity of the compartments resolved by efflux analysis. Pretreatment at high temperature or application of 2-chloro-ethanol, sodium dodecyl sulphate or hydrogen peroxide made it possible to distinguish the metabolic (cytoplasmic) phase from the remaining two (physical) phases. Likewise, varying [Pi] of the medium altered efflux and thereby [NO
3
–
]cyt, but did not affect [NO
3
–
]free space.Abbreviations and Symbols [NO
3
–
]cyt
cytoplasmic NO
3
–
concentration
- [NO
3
–
]free space
apparent-free-space NO
3
–
concentration
- [NO
3
–
]o
concentration of NO
3
–
in the external solution
-
NO
3
–
flux
- co
efflux from the cytoplasm
- oc
influx to the cytoplasm
- net
net flux
- xylem
flux to the xylem
- red/vac
combined flux to reduction and the vacuole
The research was supported by a Natural Sciences and Engineering Research Council, Canada, grant to Dr. A.D.M. Glass and by a University of British Columbia Graduate Fellowship to Herbert J. Kronzucker. Our thanks go to Dr. M. Adam and Mr. P. Culbert at the particle accelerator facility TRIUMF on the University of British Columbia Campus for providing13NO
3
–
, Drs. R.D. Guy and S. Silim for providing plant material, and Dr. M.Y. Wang, Mr. J. Mehroke and Mr. P. Poon for assistance in experiments and for helpful discussions. 相似文献
8.
Basolateral plasma membrane localization of ouabain-sensitive sodium transport sites in the secretory epithelium of the avian salt gland 下载免费PDF全文
The distribution of Na+ pump sites (Na+-K+-ATPase) in the secretory epithelium of the avian salt gland was demonstrated by freeze-dry autoradiographic analysis of [(3)H] ouabain binding sites. Kinetic studies indicated that near saturation of tissue binding sites occurred when slices of salt glands from salt-stressed ducks were exposed to 2.2 μM ouabain (containing 5 μCi/ml [(3)H]ouabain) for 90 min. Washing with label-free Ringer's solution for 90 min extracted only 10% of the inhibitor, an amount which corresponded to ouabain present in the tissue spaces labeled by [(14)C]insulin. Increasing the KCl concentration of the incubation medium reduced the rate of ouabain binding but not the maximal amount bound. In contrast to the low level of ouabain binding to salt glands of ducks maintained on a freshwater regimen, exposure to a salt water diet led to a more than threefold increase in binding within 9-11 days. This increase paralleled the similar increment in Na+-K+-ATPase activity described previously. [(3)H]ouabain binding sites were localized autoradiographically to the folded basolateral plasma membrane of the principal secretory cells. The luminal surfaces of these cells were unlabeled. Mitotically active peripheral cells were also unlabeled. The cell-specific pattern of [(3)H]ouabain binding to principal secretory cells and the membrane-specific localization of binding sites to the nonluminal surfaces of these cells were identical to the distribution of Na+-K+-ATPase as reflected by the cytochemical localization of ouabain-sensitive and K+-dependent nitrophenyl phosphatase activity. The relationship between the nonluminal localization of Na+-K+-ATPase and the possible role of the enzyme n NaCl secretion is considered in the light of physiological data on electrolyte transport in salt glands and other secretory epithelia. 相似文献
9.
10.
To show the relationship of the monodelphic species of Trichodoridae with the nominal taxa, the genus Monotrichodorus is redefined, with the addition of one new species. The new genus Allotrichodorus is proposed on the basis of new species found in Brazil; and one new species is described in the genus Paratrichodorus. 相似文献