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1.
2.
George A. Clarkson 《BMJ (Clinical research ed.)》1905,1(2299):118-119
3.
4.
When young wheat (Triticum aestivum L.) or barley (Hordeum vulgare L.) plants were deprived of an external sulphate supply (-S plants), the capacity of their roots to absorb sulphate, but not phosphate or potassium, increased rapidly (derepression) so that after 3–5 d it was more than tenfold that of sulphate-sufficient plants (+S plants). This increased capacity was lost rapidly (repression) over a 24-h period when the sulphate supply was restored. There was little effect on the uptake of L-methionine during de-repression of the sulphate-transport system, but S input from methionine during a 24-h pretreatment repressed sulphate influx in both+S and-S plants.Sulphate influx of both+S and-S plants was inhibited by pretreating roots for 1 h with 4,4-diisothiocyanatostilbene-2,2-disulphonic acid (DIDS) at concentrations > 0.1 mol · m-3. This inhibition was substantially reversed by washing for 1 h in DIDS-free medium before measuring influx. Longer-term pretreatment of roots with 0.1 mol·m-3 DIDS delayed de-repression of the sulphatetransport system in-S plants but had no influence on+S plants in 3 d.The sulphydryl-binding reagent, n-ethylmaleimide, was a very potent inhibitor of sulphate influx in-S roots, but was much less inhibitory in +S roots. Its effects were essentially irreversible and were proportionately the same at all sulphate concentrations within the range of operation of the high-affinity sulphate-transport system. Inhibition of influx was 85–96% by 300 s pretreatment by 0.3 mol·m-3
n-ethylmaleimide. No protection of the transport system could be observed by including up to 50 mol·m-3 sulphate in the n-ethylmaleimide pre-treatment solution. A similar differential sensitivity of-S and+S plants was seen with p-chloromercuriphenyl sulphonic acid.The arginyl-binding reagent, phenylglyoxal, supplied to roots at 0.25 or 1 mol·m-3 strongly inhibited influx in-S wheat plants (by up to 95%) but reduced influx by only one-half in+S plants. The inhibition of sulphate influx in-S plants was much greater than that of phosphate influx and could not be prevented by relatively high (100 mol·m-3 sulphate concentrations accompanying phenylglyoxal treatment. Effects of phenylglyoxal pretreatment were unchanged for at least 30 min after its removal from the solution but thereafter the capacity for sulphate influx was restored. The amount of new carrier appearing in-S roots was far greater than in+S roots over a 24-h period.The results indicate that, in the de-repressed state, the sulphate transporter is more sensitive to reagents binding sulphydryl and arginyl residues. This suggests a number of strategies for identifying the proteins involved in sulphate transport.Abbreviations DIDS
4,4-diisothiocyanatostilbene-2,2-disulphonic acid
- NEM
n-ethylmaleimide
- PCMBS
p-chloromercuriphenyl sulphonic acid 相似文献
5.
Valérie Toulon Hervé Sentenac Jean-Baptiste Thibaud André Soler David Clarkson Claude Grignon 《Planta》1989,179(2):235-241
The effect of HCO
3
-
on ion absorption by young corn roots was studied in conditions allowing the independent control of both the pH of uptake solution and the CO2 partial pressure in air bubbled through the solution. The surface pH shift in the vicinity of the outer surface of the plasmalemma induced by active H+ excretion was estimated using the initial uptake rate of acetic acid as a pH probe (Sentenac and Grignon (1987) Plant Physiol. 84, 1367). Acetic acid and orthophosphate uptake rates and NO
3
-
accumulation were slowed down, while 86Rb+ uptake and K+ accumulation rates were increased by HCO
3
-
. These effects were similar to those induced by 4-(2-hydroxyethyl)-1-piperazineethane sulfonic acid/2-amino-2-(hydroxymethyl)-1,3-propanediol (Hepes-Tris). They were more pronounced when the H+ excretion was strong, were rapidly reversible and were not additive to those of Hepes-Tris. The hypothesis is advanced that the buffering system CO2/H2CO3/HCO
3
-
accelerated the diffusion of equivalent H+ inside the cell wall towards the medium. This attenuated the surface pH shift in the vicinity the plasma membrane and affected the coupling between the proton pump and cotransport systems.Abbreviations FW
fresh weight
- Hepes
4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid
- Jaa
acetic acid influx
- JK
+
K+ influx
- JPi
orthophosphate influx
- Mes
2-(N-morpholino)ethanesulfonic acid
- pCO2
CO2 partial pressure
- Tris
2-amino-2-(hydroxymethyl)-1,3-propanediol 相似文献
6.
Characterization of the ''unusual'' mobility of large circular DNAs in pulsed field-gradient electrophoresis. 总被引:33,自引:4,他引:29 下载免费PDF全文
S M Beverley 《Nucleic acids research》1988,16(3):925-939
Large circular amplified DNAs (30 and 85 kb) present in methotrexate-resistant Leishmania major appear to migrate anomalously in pulsed field-gradient electrophoresis (PFGE), exhibiting pulse time-dependent mobility and migrating along a different apparent path relative to the large linear chromosomal DNAs. Quantitative studies indicate that the relative pulse-time dependence is actually conferred by the mobility properties of the large linear DNAs. One contributing factor to the difference in migration path is variability in the intrinsic voltage-dependence of mobility of supercoiled and linear DNAs, in combination with the asymmetrical/inhomogeneous voltage gradients. Certain linear chromosomes exhibit a previously undescribed pulse-time dependence in the voltage-dependence of mobility. When enzymatically relaxed or physically nicked the large circular DNAs fail to leave the well using any pulse time, a property also observed in conventional electrophoresis. These findings are relevant to PFGE theory, and its application to the study of circular DNA amplification in Leishmania and other species. 相似文献
7.
Effect of nitrogen stress and abscisic acid on nitrate absorption and transport in barley and tomato
F. Stuart Chapin III David T. Clarkson John R. Lenton Colin H. S. Walter 《Planta》1988,173(3):340-351
The potential of barley (Hordeum vulgare L.) and tomato (Lycopersicon esculentum Mill.) roots for net NO
3
-
absorption increased two-to five fold within 2 d of being deprived of NO
3
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supply. Nitrogen-starved barley roots continued to maintain a high potential for NO
3
-
absorption, whereas NO
3
-
absorption by tomato roots declined below control levels after 10 d of N starvation. When placed in a 0.2 mM NO
3
-
solution, roots of both species transported more NO
3
-
and total solutes to the xylem after 2 d of N starvation than did N-sufficient controls. However, replenishment of root NO
3
-
stores took precedence over NO
3
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transport to the xylem. Consequently, as N stress became more severe, transport of NO
3
-
and total solutes to the xylem declined, relative to controls. Nitrogen stress caused an increase in hydraulic conductance (L
p) and exudate volume (J
v) in barley but decrased these parameters in tomato. Nitrogen stress had no significant effect upon abscisic acid (ABA) levels in roots of barley or flacca (a low-ABA mutant) tomato, but prevented an agerelated decline in ABA in wild-type tomato roots. Applied ABA had the same effect upon barley and upon the wild type and flacca tomatoes: L
p and J
v were increased, but NO
3
-
absorption and NO
3
-
flux to the xylem were either unaffected or sometimes inhibited. We conclude that ABA is not directly involved in the normal changes in NO
3
-
absorption and transport that occur with N stress in barley and tomato, because (1) the root ABA level was either unaffected by N stress (barley and flacca tomato) or changed, after the greatest changes in NO
3
-
absorption and transport and L
p had been observed (wild-type tomato); (2) changes in NO
3
-
absorption/transport characteristics either did not respond to applied ABA, or, if they did, they changed in the direction opposite to that predicted from changes in root ABA with N stress; and (3) the flacca tomato (which produces very little ABA in response to N stress) responded to N stress with very similar changes in NO
3
-
transport to those observed in the wild type.Abbreviation and symbols ABA
abscisic acid
- Jv
exudate volume
- Lp
root hydraulic conductance 相似文献
8.
Clustering of hypervariable minisatellites in the proterminal regions of human autosomes 总被引:42,自引:0,他引:42
Six of the human minisatellites detected by DNA fingerprint probes have been localized by in situ hybridization to human metaphase chromosomes. These hypervariable loci are not dispersed at random in the human genome, but show preferential, though not exclusive, localization to terminal G-bands of human autosomes. Two of the proterminal minisatellites are very closely linked to other variable loci. Sequence analysis of one of these additional minisatellites suggests that the two linked minisatellites arose by independent amplification of different repeat units. The proterminal regions of human autosomes may therefore be rich in minisatellites, analogous to the pseudoautosomal terminal pairing region of human sex chromosomes that is similarly abundant in hypervariable minisatellites. 相似文献
9.
Unstable amplification of two extrachromosomal elements in alpha-difluoromethylornithine-resistant Leishmania donovani. 下载免费PDF全文
We describe the first example of unstable gene amplification consisting of linear extrachromosomal DNAs in drug-resistant eukaryotic cells. alpha-Difluoromethylornithine (DFMO)-resistant Leishmania donovani with an amplified ornithine decarboxylase (ODC) gene copy number contained two new extrachromosomal DNAs, both present in 10 to 20 copies. One of these was a 140-kb linear DNA (ODC140-L) on which all of the amplified copies of the odc gene were located. The second was a 70-kb circular DNA (ODC70-C) containing an inverted repeat but lacking the odc gene. Both ODC140-L and ODC70-C were derived from a preexisting wild-type chromosome, probably by a conservative amplification mechanism. Both elements were unstable in the absence of DFMO, and their disappearance coincided with a decrease in ODC activity and an increase in DFMO growth sensitivity. These results suggest the possibility that ODC70-C may play a role in DFMO resistance. These data expand the diversity of known amplification mechanisms in eukaryotes to include the simultaneous unstable amplification of both linear and circular DNAs. Further characterization of these molecules will provide insights into the molecular mechanisms underlying gene amplification, including the ability of linear amplified DNAs to acquire telomeres and the determinants of chromosomal stability. 相似文献
10.
Stefan Jansson Eran Pichersky Roberto Bassi Beverley R. Green Masahiko Ikeuchi Anastasios Melis David J. Simpson Michael Spangfort L. Andrew Staehelin J. Philip Thornber 《Plant Molecular Biology Reporter》1992,10(3):242-253
We propose a nomenclature for the genes encoding the chlorophylla/b-binding proteins of the light-harvesting complexes of photosystem I and II. The genes encoding LHC I and LHC II polypeptides
are namedLhca1 throughLhca4 andLhcb1 throughLhcb6, respectively. The proposal follows the general format recommended by the Commision on Plant Gene Nomenclature. We also present
a table for the conversion of old gene names to the new nomenclature. 相似文献