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1.
Ishikawa Hideo; Matsuura Keitaro; Yamamura Sadao; Ohta Eiji; Sakata Makoto 《Plant & cell physiology》1984,25(3):359-365
Two simultaneous measurements, extracellular potential V andK$(86Rb) transport, and the intracellular potential of corticalcell E and potential V, were used to study the effects of externalKCl on two-day-old bean roots. High, external KCl concentrations(>10 mM) markedly enhanced K$ loss from tissues in the elongatingregion to the external solution and induced depolarization ofthe membrane potential difference (PD=VE). When Phaseolus roots were returned to a solution with a lowerconcentration of K$, the K$ loss and the potential difference,PD, were restored to their previous values. K$ transport fromother parts of the root to the elongating region, however, didnot recover, and the potential, E, increased. These resultsclearly demonstrate that treatment of Phaseolus roots with ahigh external K$ concentration inhibits K$ translocation throughthe stele to the elongating cortical cells and is dependenton depolarization of the intracellular potential. (Received October 14, 1983; Accepted January 20, 1984) 相似文献
2.
Influx and Efflux of Phosphorus in Roots of Wheat Plants in Non-Growth-Limiting Concentrations of Phosphorus 总被引:5,自引:0,他引:5
The regulation of net phosphorus uptake was studied in wheatplants at ambient non-growth-limiting P-concentrations. Wheat(Triticum aestivum cv. Klein Atalaya) seedlings were grown fromgermination in culture solutions containing 0.05, 0.5 and 5.0mol m3 phosphate. Only small increments in plant P-concentrationand specific accumulation rate for phosphorus were found whenambient P-concentration was increased 100 times. P-influx, estimatedby 32P-uptake, was markedly greater with increased externalP-concentration, but only small changes in Vmax and no changesin Km were found. Indirect estimation of P-efflux in a time-courseof 32P-uptake, and direct P-efflux measurements in washout experiments indicated that P-efflux markedly increasedin higher ambient P-concentration. The increase in P-effluxalmost completely neutralized the higher P-influx observed in5.0 mol m3 relative to 0.05 mol m3 phosphate.It is postulated that in non-limiting P-concentration net P-uptakeis mainly controlled by P-efflux. Key words: Net P uptake, 32P, kinetic parameters 相似文献
3.
《生物化学与生物物理学报:生物膜》1985,814(1):50-56
The influx rate of 86Rb decreases during accumulation of K+ or Rb+ into metabolizing yeast cells under anaerobic conditions with glucose as substrate. Possible causes for the decrease in the influx rate are examined. It is ruled out that the decrease in the influx rate is caused by an increased turgor pressure of the cells or to an impairment of their energization. During the accumulation of K+ or Rb+, no decrease but an increase in the protonmotive force of the cells is found. The concomitant increase in cell pH accounts only in small part for the decrease in the influx rates. Acidification of the cells on adding butyrate to the suspension causes a transient increase in the influx rates, whereas the cellular monovalent cation content is still increased. Consequently, no direct relationship is found between the influx rate and the cellular content of K+ and Rb+. 相似文献
4.
Maize plants were grown in nutrient solution without phosphate,or in which inorganic phosphate (Pi) was maintained at nearlyconstant concentrations of 1 µM, 10µM or 0·5mM. In vivo 31P-NMR measurements showed that there was no discernibledifference in the cytoplasmic Pi content (µmol cm3root volume) of the mature roots of plants exposed to 1 µM,10µM or 0·5 mM external phosphate for up to 12d. However, the vacuolar Pi content of the mature roots variedabout 10-fold between these three groups. The cytoplasmic Pi content of roots receiving no external phosphatedecreased significantly after about 7 d total growth, and atabout this time the vacuolar pool of Pi became too small foraccurate measurement. The presence of 1 µM Pi in the nutrientsolution completely prevented this decline in cytoplasmic Pi,and there was some evidence that it also raised the Pi contentof the root vacuoles above the almost undetectable level foundin the totally P-starved roots. During the first 79 d of growth, the nucleoside triphosphatecontent of the mature roots was unaffected by the concentrationof phosphate in the nutrient solution. The results highlight the close control of cytoplasmic concentrationsof certain important phosphorus metabolites in roots growingin soil of normal agricultural fertility. Key words: Vacuole, cytoplasm, intracellular compartmentation, NTP, P-nutrition 相似文献
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Uptake of Rb+ was investigated in 6–8-day-old intact barley plants (Hordeum vulgare cv. Kristina), which had been cultivated or pretreated in nutrient solutions with various K+ concentrations. The relationship between Rb+ influx and the K+ concentration of roots appeared to be sigmoidal for plants grown in solutions containing K+, indicating regulation of Rb+ uptake by allosteric inhibition of the uptake mechanism. Pretreatment of the roots in K+-free solutions changed the pattern of uptake and caused the Rb+ influx to become linearly related to the chemical Rb+ potential of the uptake solution. Pretreatment in K+-free solutions probably abolishes the allosteric inhibition of a carrier system. 相似文献
8.
Presence of Two Different Membrane-bound, KCl-stimulated Adenosine Triphosphatase Activities in Maize Roots 总被引:5,自引:5,他引:0
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Recent publications have indicated that a KCl-stimulated ATPase from cereal roots is specifically associated with plasmalemma-enriched membrane fractions. However, in previous work we found that relatively high specific activities of this enzyme were also associated with a membrane fraction which did not contain plasmalemma. In an attempt to clarify this discrepancy, we have investigated the effect of density gradient composition upon the association of the enzyme with different membrane fractions isolated from the roots of Zea mays L. (WF9 × M14). 相似文献
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Red light-induced changes in the gravitropism of roots of Zea mays variety Merit is a very low fluence response with a threshold of 10−9 moles per square meter and is not reversible by far red light. Blue light also affects root gravitropism but the sensitivity of roots to blue is 50 to 100 times less than to an equal fluence of red. In Z. mays Merit we conclude that phytochrome is the sole pigment associated with light-induced changes in root gravitropism. 相似文献
11.
Origins of the Electrical Potential Difference between the Xylem Sap of Maize Roots and the External Solution 总被引:1,自引:0,他引:1
The effects of 2,4-dinitrophenol, of changes in the temperatureand concentration of the ambient solution and of variationsin salt status on the electrical potential difference betweenthe xylem exudate of maize roots and the ambient solution havebeen examined. The results are discussed in the light of someof the factors which could give rise to a potential differencebetween the sap and the solution. The rapid response of thepotential difference to dinitrophenol and to changes in temperaturesuggest that, at least in part, it arises directly from metabolicprocesses. Rapid changes in the potential difference broughtabout by addition of salts may be attributed to differentialrates of movement of anions and cations in the initial uptakeprocess. Over longer periods the potential difference appearsto be dependent on the concentration, but not the compositionof the ambient solution, and on the salt status of the roots.The salt status influences the relative rates at which anionsand cations are transported to the xylem sap, and a correlationhas been found between the potential difference and the ratioof the rates of movement of chloride or sulphate to potassiumto the sap. The implications of these findings on the elucidationof the pathways whereby ions are transported to the sap arediscussed. 相似文献
12.
Simultaneous measurements of the extracellular potential andthe K+(86Rb) efflux, and of the intracellular and extracellularpotentials of the cortical cells were used to study the effectsof external Ca2+ on the plasma membrane K+(86Rb) permeabilityin two-day-old mung bean (Vigna mungo L. Hepper, Blackmatpe) roots under high KCl stress. The K+ efflux wasenhanced by a high KCl solution (>7.5 mM), and addition of0.5 mM Ca2+ could suppress this efflux. The removal of membrane-associatedCa+ from the root surface with EDTA led to a recovery of theK+ efflux along with a marked decrease in the extracellularpotential. (Received November 19, 1986; Accepted March 6, 1987) 相似文献
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药物诱导的玉米根尖细胞凋亡 总被引:10,自引:0,他引:10
同时应用DNA Laddering、DNA Gel Blot以及基于染色体涂片 原位末端标记技术,从染色体、细胞核和DNA不同水平对细胞毒素类药和的放线菌D、放线菌酮和秋水仙碱诱导的玉米(Zea mays L.)根尖分生组织细胞死亡作了检测。结果表明:同动物中一样,这些药物诱导的玉米根尖分生组织细胞死亡也具有DNA Ladder、染色质和细胞核浓缩等典型的调亡特征,说明这些细胞毒素类药物能够诱导植 相似文献
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玉米根细胞膜铁氰化钾还原酶 总被引:2,自引:0,他引:2
玉米根细胞膜制剂具有明显的NADH一铁氰J也钾还原酶(FCR)活性。铁氰化钾被还原的同时伴有质子跨膜运输,所形成的△μH+既不受H+-ATPase抑制剂的影响,也不需要ATP的存在,反应最适PH为6.5。FCR对NADH和铁氰化钾具有较高的活性反应,(Km分别为42和70μmol/L,Vmax分别为1.84和2.10μmol/mgproteinmin)。而对NADPH.只有微弱的反应活性(Vmax为0.042μmol/mgproteinmin)。用FCR的潜在活性证实在膜的胞质一侧存在底物结合部位。Mg2+、Mn2+、Ca2+、K+、Na+对酶均有一定的激活作用,以Mn2+最强、其次为Mg2+。 相似文献
16.
Ishikawa Hideo; Yamamura Ken; Furukoshi Michiaki; Ohta Eiji; Sakata Makoto 《Plant & cell physiology》1984,25(6):1045-1051
The three-phase electric potential distribution along two-day-oldintact Phaseolus roots was investigated in relation to cellgrowth and K$ and H$ transports using tracer K$(86Rb) and pHexperiments. The activity of a radial electrogenic componentlocated between the cortical cells and the external solutionwas high in the elongating region and in the completely maturedregion. The activity of another radial electrogenic componentlocated between the cortical cells and the stele was maximalin the elongating region. Both potassium uptake from the externalsolution into the cortical cells and H$ excretion took placemainly in these regions. (Received November 9, 1983; Accepted June 21, 1984) 相似文献
17.
Photosynthesis, Respiration, and Carbon Assimilation in Water-Stressed Maize at Two Oxygen Concentrations 总被引:3,自引:1,他引:2
Photosynthesis decreased with decreasing leaf water potentialas a consequence of stomatal closure and possibly non-stimataleffects of severe stress. Assimilation ceased at c. 16x 105Pa. Photo-respiration, in 21% O2, was small in relation to assimilationin unstressed leaves and decreased as leaf water potential fellbut it was much larger in proportion to photosynthesis at severestress. Decreasing the O2 content to 1.5% increased photosynthesisslightly and decreased photo-respiration but did not changethe stress at which assimilation stoped. Dark respiration wasinsensitive to both O2 and stress. Less 14C accumulated in stressedleaves but in 21% O2 a greater proportion of it was in aminoacids, particularly glycine and serine. 1.5% O2 decreased the14C in glycine to 10% and in serine to 50% of their levels in21% O2. In both O2 concentrations the proportion of 14C in serineincreased only at the most severe stress. Gas exchange measurementsand changes in the 14C flux to glycine are interpreted as theresult of glycolate pathway metabolism increasing as a proportionof assimilation in stressed leaves in high O2. The small absoluterate of photorespiration in high O2 and at low leaf water potentialmay be due to slow rates of glycine decarbodylation as wellas efficient fixation of any CO2 produced. Serine is synthesizedby an O2-sensitive pathway and an O2-insensitive pathway, whichis most active at severe stress. Synthesis of alanine competeswith that of glycine and serine for a common precursor suppliedby the photo-synthetic carbon reduction cycle. The relativespecific radioactivities of aspartate and alanine suggest thatthey are derived from a common precursor pool, probably pyruvatefrom 3-PGA. The amounts of 3-PGA, aspartate, malate, alanine,and sucrose decreased with increasing water stress as a consequenceof slower assimilation and pool filling. Other amino acids,glycine, serine, glutamate, and proline, accumulated at lowwater potential possibly due to increased synthesis and slowerrates of consumption. Changes in pool sizes, carbon fludes,and specific activities of metabolites are related to the mechanismof C4 photosynthesis and current concepts of glycolate pathwaymetabolism. 相似文献
18.
Feedback Regulation of Nitrate Influx in Barley Roots by Nitrate,Nitrite, and Ammonium 总被引:23,自引:5,他引:18
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The short-lived radiotracer 13N was used to study feedback regulation of nitrate influx through the inducible high-affinity transport system of barley (Hordeum vulgare L. cv Steptoe) roots. Both wild-type plants and the mutant line Az12:Az70 (genotype nar1a;nar7w), which is deficient in the NADH-specific and NAD(P)H-bispecific nitrate reductases (R.L. Warner, R.C. Huffaker [1989] Plant Physiol 91: 947-953) showed strong feedback inhibition of nitrate influx within approximately 5 d of exposure to 100 fmu]M nitrate. The result with the mutant, in which the flux of nitrogen into reduced products is greatly reduced, indicated that nitrate itself was capable of exercising feedback regulation upon its own influx. This conclusion was supported by the observation that feedback in wild-type plants occurred in both the presence and absence of L-methionine sulfoximine, an inhibitor of ammonium assimilation. Nitrite and ammonium were also found to be capable of exerting feedback inhibition upon nitrate influx, although it was not determined whether these ions themselves or subsequent metabolites were responsible for the effect. It is suggested that feed-back regulation of nitrate influx is potentially mediated through several nitrogen pools, including that of nitrate itself. 相似文献
19.
Rapid release of 42K or 86Rb from two distinct transport sites on the Na,K-pump in the presence of Pi or vanadate 总被引:1,自引:0,他引:1
B Forbush 《The Journal of biological chemistry》1987,262(23):11116-11127
The rate of 86Rb or 42K release from an occluded form of the phosphorylated Na+ pump has been studied using a rapid filtration apparatus described previously. The rate constant of release is 5-15 s-1, and 42K and 86Rb dissociate at approximately the same rate. Mg2+ is required for deocclusion in the presence of Pi at a site which has the same affinity as the site involved in stabilization of E2(K) with ATP; we propose that Na,K-ATPase has only one site for Mg2+ (apart from Mg2+ complexed with ATP), that the affinity of this site for Mg2+ is increased by Pi binding and decreased by ATP binding, and that Mg2+ is bound and released in the normal transport cycle. In the presence of K+, Cs+, Rb+, or Tl+, the release of two distinct 86Rb ions can be observed, the slow release from one site ("s" site) being blocked by occupancy of the site vacated by the other ("f", fast site). By a sequence of incubations, labeled 86Rb can be placed at either site, and the rate of dissociation monitored individually; in the absence of K+, dissociation from the s site proceeds after a lag in which the f site is vacated. The results are consistent with a "flickering-gate" model of deocclusion to the extracellular pump face, in which the site is exposed to the medium only long enough for a single ion to be released. When deocclusion to the intracellular face is promoted with ATP, ions are released from both sites at the same rate, presumably because the E2----E1 conformational change is rate-limiting. Unlabeled ions co-occluded with 86Rb increase the ATP-stimulated rate of release in the order Rb+ less than Tl+ less than Cs+ less than K+; since the same rank order is observed when dissociation from the s site is monitored in the presence of these ions and MgPi we propose that the latter process proceeds toward the intracellular pump face. 86Rb release from the vanadate-inhibited enzyme has the characteristics of Pi-stimulated release but is approximately 25-fold slower. ATP binds to both the phosphorylated and vanadate-inhibited forms of Na,K-ATPase and increases the rate of deocclusion, apparently to both the intracellular and extracellular faces of the pump. 相似文献
20.
Radial Exchange of Labeled Water in Intact Maize Roots 总被引:7,自引:7,他引:0
Joseph T. Woolley 《Plant physiology》1965,40(4):711-717