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1.
An investigation was carried out to study the cation-anion balance in different tissues of tomato plants supplied with nitrate, urea, or ammonium nitrogen in water culture. Irrespective of the form of nutrition, a very close balance was found in the tissues investigated (leaves, petioles, stems, and roots) between total cations (Ca, Mg, K and Na), and total anions (NO3−, H2PO4−, SO4−−, Cl−) total non-volatile organic acids, oxalate, and uronic acids. In comparison with the tissues of the nitrate fed plants, the corresponding ammonium tissues contained lower concentrations of inorganic cations, and organic acids and a correspondingly higher proportion of inorganic anions. Tissues from the urea plants were intermediate between the other 2 treatments. These results were independent of concentration or dilution effects, caused by growth. In all tissues approximately equivalent amounts of diffusible cations (Ca++, Mg++, K+ and Na+), and diffusible anions (No3−, SO4−−, H2PO4−, Cl−) and non-volatile organic acids were found. An almost 1:1 ratio occurred between the levels of bound calcium and magnesium, and oxalate and uronic acids. This points to the fact that in the tomato plant the indiffusible anions are mainly oxalate and pectate. Approximately equivalent values were found for the alkalinity of the ash, and organic anions (total organic acids including oxalate, and uronic acids). The influence of nitrate, urea, and ammonium nitrogen nutrition on the cation-anion balance and the organic acid content of the plant has been considered and the effects of these different nitrogen forms on both the pH of the plant and the nutrient medium and its consequences discussed. 相似文献
2.
Effects of several organic acids on ion uptake and retention and on respiration in barley roots having low and high KCl contents were assayed by measurements of K +, Na +, Ca 2+, Cl −, and oxygen uptake. Organic acids with high pK a values increase the permeability of roots to ions and decrease respiration when present in sufficient concentrations at pH 5 but have no inhibitory effects at pH 7. Absence of respiratory inhibition in short times and at lower organic acid concentrations, under conditions that immediately produce a permeability increase, indicate that the permeability change is not a result of respiratory inhibition. Effects of formate, acetate, propionate, and glutarate are attributed to entry of undissociated acid molecules into the effective membranes. Lack of a permeability increase with succinate, which has lower distribution coefficients to lipid solvents than do the aliphatic acids, can be explained by failure of sufficient amounts of the hydrophilic succinic acid molecules to penetrate the membranes involved. These experiments suggest that undissociated acid in root membranes can increase permeability of the roots. 相似文献
3.
The accumulation of inorganic and organic osmolytes and their role in osmotic adjustment were investigated in roots and leaves
of vetiver grass ( Vetiveria zizanioides) seedlings stressed with 100, 200, and 300 mM NaCl for 9 days. The results showed that, although the contents of inorganic
(K +, Na +, Ca 2+, Mg 2+, Cl −, NO 3−, SO 42− and H 2PO 3−)) and organic (soluble sugar, organic acids, and free amino acids) osmolytes all increased with NaCl concentration, the contribution
of inorganic ions (mainly Na +, K +, and Cl −) to osmotic adjustment was higher (71.50–80.56% of total) than that of organic solutes (19.43–28.50%). The contribution of
inorganic ions increased and that of organic solutes decreased in roots with the enhanced NaCl concentration, whereas the
case in leaves was opposite. On the other hand, the osmotic adjustment was only effective for vetiver grass seedlings under
moderate saline stress (less than 200 mM NaCl). 相似文献
4.
K +-stimulated ATPase activity of a plasmalemma-enriched fraction from excised roots of oat was triphasic in the range 5 to 80 millimolar KCl. The phases obeyed Michaelis-Menten kinetics and were separated from each other by jumps or sharp breaks at about 10 and 20 millimolar. Stimulation by alkali cations was in the order K + > Rb + > Na + > Cs + > Li + or in a closely related sequence. The specificity reflected differences in Vmax, not in affinity ( Km−1). Stimulation by the organic cations ethanolamine and choline in the interval 11 to 80 millimolar appeared monophasic rather than biphasic. Substitution on the quaternary nitrogen of the amino alcohols decreased their effectiveness, as did extension and branching of the chain. Stimulation was maximal at about pH 7 both for K + and choline. 相似文献
5.
A detailed examination was conducted on the linear, or first-order kinetic component for K +( 86Rb +) influx into root segments of both low- and high-salt grown corn seedlings ( Zea mays [A632 × Oh 43]). In tissue from both low- and high-salt grown roots, replacement of Cl − in the uptake solution by either SO 42−, H 2PO 4−, or NO 3− caused a significant (50-60%) and specific inhibition of the linear component of K + influx. The anion transport inhibitor, 4,4′-diisothiocyano-2,2′-disulfonic acid, was found to abolish saturable Cl − influx in corn roots while causing a significant (50-60%) and specific inhibition of the linear K + uptake system; this inhibition was identical to that observed when Cl − was replaced by other anions in the K + uptake solution. Additionally, the quaternary ammonium cation, tetraethylammonium, which has been shown to block K + channels in nerve axons, also caused a dramatic (70%) and specific inhibition of the linear component of K + influx, but this was obtained only in high-salt roots. The reasons for this difference are discussed with respect to the differing abilities of low- and high-salt roots to absorb tetraethylammonium. Our present results indicate that the linear component of K+ influx may occur by a passive process involving transmembrane K+ channels. Fluxes through these K+ channels may be partly coupled to a saturating Cl− influx mechanism. 相似文献
6.
The influence of NO 3− uptake and reduction on ionic balance in barley seedlings ( Hordeum vulgare, cv. Compana) was studied. KNO 3 and KCl treatment solutions were used for comparison of cation and anion uptake. The rate of Cl − uptake was more rapid than the rate of NO 3− uptake during the first 2 to 4 hours of treatment. There was an acceleration in rate of NO 3− uptake after 4 hours resulting in a sustained rate of NO 3− uptake which exceeded the rate of Cl − uptake. The initial (2 to 4 hours) rate of K + uptake appeared to be independent of the rate of anion uptake. After 4 hours the rate of K + uptake was greater with the KNO 3 treatment than with the KCl treatment, and the solution pH, cell sap pH, and organic acid levels with KNO 3 increased, relative to those with the KCl treatment. When absorption experiments were conducted in darkness, K + uptake from KNO 3 did not exceed K + uptake from KCl. We suggest that the greater uptake and accumulation of K + in NO 3−-treated plants resulted from ( a) a more rapid, sustained uptake and transport of NO 3− providing a mobile counteranion for K + transport, and ( b) the synthesis of organic acids in response to NO 3− reduction increasing the capacity for K + accumulation by providing a source of nondiffusible organic anions. 相似文献
7.
Soybeans ( Glycine max L. Merr., cv Kingsoy) were grown on media containing NO 3− or urea. The enrichments of shoots in K +, NO 3−, and total reduced N (N r), relative to that in Ca 2+, were compared to the ratios K +/Ca 2+,NO 3−/Ca 2+, and N r/Ca 2+ in the xylem saps, to estimate the cycling of K +, and N r. The net production of carboxylates (R −) was estimated from the difference between the sums of the main cations and inorganic anions. The estimate for shoots was compared to the theoretical production of R − associated with NO 3− assimilation in these organs, and the difference was attributed to export of R − to roots. The net exchange rates of H + and OH − between the medium and roots were monitored. The shoots were the site of more than 90% of total NO 3− reduction, and N r was cycling through the plants at a high rate. Alkalinization of the medium by NO 3−-fed plants was interrupted by stem girdling, and not restored by glucose addition to the medium. It was concluded that the majority of the base excreted in NO 3− medium originated from R − produced in the shoots, and transported to the roots together with K +. As expected, cycling of K + and reduced N was favoured by NO 3− nutrition as compared to urea nutrition. 相似文献
8.
Nitrogen form has been shown to affect Zn uptake, translocation and storage in the Zn-hyperaccumulating plant Noccaea caerulescens but the biochemical processes are not fully understood. Organic acids and amino acids have been implicated in Zn transport and storage. This study aimed to examine the effect of N form on concentrations of organic acids and amino acids and how these metabolites correlated with Zn hyperaccumulation. Plants were grown in nutrient solution with NO 3−, NH 4NO 3 or NH 4+, supplied with 50 or 300 μM Zn, and buffered at either pH 4.5 or 6.5. The metabolomic profile was determined by gas chromatography mass spectroscopy. The concentration of Zn in shoots, xylem and roots was greatest for the NO 3−, pH 6.5 and 300 μM Zn treatments. For all N forms, the lower growth-medium pH raised xylem sap pH but had no influence on Zn concentration or exudation rate of the xylem sap. Nitrate enhanced organic acid production while NH 4+ increased amino acid production. Organic acids in the xylem were more responsive to changes in growth-medium pH than N form, and did not correlate with Zn concentration in shoots, roots or xylem. Serine might be directly involved in Zn hyperaccumulation. Phosphoric acid was associated with reduced Zn accumulation in the shoots. Malic acid was not detected in the shoots but responded to cation uptake more than to Zn specifically in the roots. Citric acid responded to cation uptake more than to Zn specifically in the shoots but did not correlate with Zn concentration in the roots or the xylem sap, or any other cations in the roots. In conclusion, organic acids in N. caerulescens are not specifically involved in Zn hyperaccumulation but are involved in regulating pH in the xylem and cation–anion balance in plants. 相似文献
9.
Four selected NaCl-tolerant cell lines of Sour orange ( Citrus aurantium) were compared with the nonselected cell line in their growth and internal ion content of Na +, K +, and Cl − when exposed to increasing NaCl concentrations. No difference was found among the various NaCl-tolerant cell lines in Na + and Cl − uptake, and all these cell lines took up similar or even larger amounts of Na + and Cl − than the NaCl-sensitive cell line. Exposure of cells of NaCl-sensitive and NaCl-tolerant lines to equal external concentrations of NaCl, resulted in a greater loss of K + from the NaCl-sensitive cell line. This observation leads to the conclusion that growth and ability to retain high levels of internal K + are correlated. Exposure of the NaCl-tolerant cell lines to salts other than NaCl resulted in even greater tolerance to Na 2SO 4, but rather poor tolerance to K + introduced as either K 2SO 4 or KCl; the latter has a stronger inhibitory effect. The NaCl-sensitive cell line proved to be more sensitive to replacement of Na + by K +. Analyses of internal Na +, K +, and Cl − concentrations failed to identify any particular internal ion concentration which could serve as a reliable marker for salt tolerance. 相似文献
10.
Ca 2+ uptake was studied in short-term experiments using 5-day-old excised maize roots. This tissue readily absorbs Ca 2+, and inhibition by dinitrophenol and low temperature shows that the process is metabolically mediated. The uptake of Ca 2+, like that of other cations, is influenced by the counter ion, the pH and concentration of the ambient solution, and the presence of other cations. The rate of uptake from various salts decreases in the following order: NO 3− > Cl − = Br − > SO 42−. K + and H + greatly interfere with Ca 2+ absorption, while Li + and Na + have only slight effects. 相似文献
11.
The ionic composition in the leaves of some glycophyte plants ( Phaseolus vulgaris L., Lycopersicon esculentum L., and Amaranthus cruentus L.) was studied during leaf development. Plants were grown in a stationary hydroponic culture; a growth medium contained equimolar concentrations of inorganic ions (NO 3 ? , Cl ?, SO 4 2? , H 2PO 4 ? , K +, Ca 2+, Mg 2+, and Na +) equal to 5 mg-equiv./l for each ion. In the juvenile leaf, the main ions were K + and water-soluble anions of organic acids represented mainly by di-and tricarboxylic acids in kidney bean and tomato and oxalic acid in amaranth. An increase in the total amount of organic anions, coinciding with the accumulation of bivalent cations, was registered in leaves of glycophytes during their development. Mature and senescing leaves of tomato and kidney bean accumulated mainly di-and tricarboxylic acid salts with the prevalence of Ca 2+ ions. In amaranth leaves, the formation of water-insoluble (acid-soluble) oxalate pool containing Ca 2+ ions (mature leaves) or Ca 2+ and Mg 2+ ions (senescing leaves) was registered. The priority role of the metabolism of organic acids in the formation of the ionic composition of glycophyte leaves during their development is discussed. It is supposed that the species-specific ionic composition of glycophyte leaves at different developmental stages is due mainly to the pattern of carbon metabolism causing the accumulation either of di-and tricarboxylic acids or oxalic acid. 相似文献
12.
Tomato plants ( Lycopersicon esculentum L. var. Ailsa Craig) were grown in water culture in nutrient solution in a series of 10 increasing levels of nitrate nutrition. Using whole plant data derived from analytical and yield data of individual plant parts, the fate of anion charge arising from increased NO 3 assimilation was followed in its distribution between organic anion accumulation in the plant and OH − efflux into the nutrient solution as calculated by excess anion over cation uptake. With increasing NO 3 nutrition the bulk of the anion charge appeared as organic anion accumulation in the plants. OH − efflux at a maximum accounted for only 20% of the anion charge shift. The major organic anion accumulated in response to nitrate assimilation was malate. The increase in organic anion accumulation was paralleled by an increase in cation concentration (K +, Ca 2+, Mg 2+, Na +). Total inorganic anion levels (NO 3−, SO 42−, H 2PO 4−, Cl −) were relatively constant. The effect of increasing NO 3 nutrition in stimulating organic anion accumulation was much more pronounced in the tops than in the roots. 相似文献
13.
Photosynthesis, stroma-pH, and internal K + and Cl − concentrations of isolated intact chloroplasts from Spinacia oleracea, as well as ion (K +, H +, Cl −) movements across the envelope, were measured over a wide range of external KCl concentrations (1-100 millimolar). Isolated intact chloroplasts are a Donnan system which accumulates cations (K+ or added Tetraphenylphosphonium+) and excludes anions (Cl−) at low ionic strength of the medium. The internally negative dark potential becomes still more negative in the light as estimated by Tetraphenylphosphonium+ distribution. At 100 millimolar external KCl, potentials both in the light and in the dark and also the light-induced uptake of K+ or Na+ and the release of protons all become very small. Light-induced K+ uptake is not abolished by valinomycin suggesting that the K+ uptake is not primarily active. Intact chloroplasts contain higher K+ concentrations (112-157 millimolar) than chloroplasts isolated in standard media. Photosynthetic activity of intact chloroplasts is higher at 100 millimolar external KCl than at 5 to 25 millimolar. The pH optimum of CO2 fixation at high K+ concentrations is broadened towards low pH values. This can be correlated with the observation that high external KCl concentrations at a constant pH of the suspending medium produce an increase of stroma-pH both in the light and in the dark. These results demonstrate a requirement of high external concentrations of monovalent cations for CO2 fixation in intact chloroplasts. 相似文献
14.
Excised roots of barley ( Hordeum vulgare, var. Campana) were incubated in KCl, K 2SO 4, CaCl 2, and NaCl solutions at concentrations of 10 −5 to 10 −2 n. Changes in substrate solution pH, cell sap pH, and organic acid content of the roots were related to differences in cation and anion absorption. The pH of expressed sap of roots increased when cations were absorbed in excess of anions and decreased when anions were absorbed in excess of cations. The pH of the cell sap shifted in response to imbalances in cation and anion uptake in salt solutions as dilute as 10 −5 n. Changes in cell sap pH were detectable within 15 minutes after the roots were placed in 10 −3 n K 2SO 4. Organic acid changes in the roots were proportional to expressed sap pH changes induced by unbalanced ion uptake. Changes in organic acid content in response to differential cation and anion uptake appear to be associated with the low-salt component of ion uptake. 相似文献
15.
Susceptible corn roots exposed to the host-selective toxin of Helminthosporium carbonum took up and retained more NO 3−, Na +, Cl −, 3-o-methylglucose, and leucine than did control roots. Stimulatory effects on uptake were more pronounced with freshly cut roots than with roots that were washed and aged. Solutes were accumulated against a concentration gradient, and toxin-treated tissues developed a steeper gradient than did control tissues. Toxin affected both the low and high affinity uptake systems for Na + and Cl −. Toxin did not affect uptake of Na 2−, K +, Ca 2+, phosphate ion (H 2PO 4− and HPO 4−), SO 4−, and glutamic acid. No toxin-induced leakage of any solute tested was detected within 5 to 6 hr after initial exposure to toxin. The data suggest that toxin from H. carbonum does not cause the general plasma membrane derangement caused by other host-selective toxins. Instead, H. carbonum toxin may cause specific changes in characteristics of the plasmalemma, which result in increased uptake of certain solutes. 相似文献
16.
Osmotic adjustment of cultured tobacco ( Nicotiana tabacum L. var Wisconsin 38) cells was stimulated by 10 micromolar (±) abscisic acid (ABA) during adaptation to water deficit imposed by various solutes including NaCl, KCl, K 2SO 4, Na 2SO 4, sucrose, mannitol, or glucose. The maximum difference in cell osmotic potential (Ψπ) caused by ABA treatment during adaptation to 171 millimolar NaCl was about 6 to 7 bar. The cell Ψπ differences elicited by ABA were not due to growth inhibition since ABA stimulated growth of cells in the presence of 171 millimolar NaCl. ABA caused a cell Ψπ difference of about 1 to 2 bar in medium without added NaCl. Intracellular concentrations of Na +, K +, Cl −, free amino acids, or organic acids could not account for the Ψπ differences induced by ABA in NaCl treated cells. However, since growth of NaCl treated cells is more rapid in the presence of ABA than in its absence, greater accumulation of Na +, K +, and Cl − was necessary for ion pool maintenance. Higher intracellular sucrose and reducing sugar concentrations could account for the majority of the greater osmotic adjustment of ABA treated cells. More rapid accumulation of proline associated with ABA treatment was highly correlated with the effects of ABA on cell Ψπ. These and other data indicate that the role of ABA in accelerating salt adaptation is not mediated by simply stimulating osmotic adjustment. 相似文献
17.
A reevaluation of the specificity of system y +, the classical transporter for cationic amino acids is presented. System y + has been defined as a transporter for cationic amino acids that binds neutral amino acids with lower affinity in the presence
of Na +. The discovery of other transporters for cationic amino has suggested that some properties, originally attributed to system
y +, may relate to other transport systems. Uncertainty concerns mainly, the affinity for neutral amino acids and the cation
dependence of this interaction. Neutral amino acids (13 analogues tested) were found to bind to system y + in human erythrocytes with very low affinity. Inhibition constants (K iy, m m) ranged between 14.2 m m and >400 m m, and the strength of interaction was similar in the presence of Na +, K + or Li + (145 m m). In choline medium, no interaction was detected up to 20 m m of the neutral amino acid. Guanidinium ion (5 m m, osmolarity maintained with choline) potentiated neutral amino acid binding; the effect was most important in the case of
l-norvaline which aligned with guanidinium ion is equivalent to arginine. This suggests cooperative interaction at the substrate
site. The specificity of system y + was shown to be clearly distinct from that of system y +L, a cationic amino acid transporter that accepts neutral amino acids with high affinity in the presence of Na + and which influenced the classical definition of system y +.
Received: 28 September 1998/Revised: 21 December 1998 相似文献
18.
After Stimulation with ATP and in the absence of divalent cations, isolated barley mesophyll vacuoles exhibited massive solute fluxes across the tonoplast, measured either as efflux of endogenous solutes or as uptake of radioactive-labeled compounds. Transported solutes were ions (particularly K +, NO
3
–
, Cl –) and amino acids (for example, ala, arg, asp, gln, leu, met). Addition of Mg 2+in excess of added ATP inhibited fluxes of inorganic ions and of positively charged amino acids, but not, or to a smaller extent, those of neutral amino acids. Thus, Mg 2+ increased the specificity of the carrier for amino acids such as alanine and glutamine. All ATP-stimulated transport processes were sensitive towards inhibition by lipophilic amino acids, for example by leucine and phenylalanine. After stimulation with sulfhydryl reagents, the inhibitory properties of Mg 2+ and lipophilic amino acids were lost. These data concur with the hypothesis of a single transporter which exhibits a channel-like structure with a low degree of substrate selectivity in the absence of Mg 2+, and which functions as a neutral amino acid carrier in the presence of Mg 2+.We are grateful to Frau Claudia Dürr for excellent technical assistance. The work was supported by the Deutsche Forschungsgemeinschaft within the Sonderforschungsbereich 176 of the Bayerische-Julius-Maximilians-Universität Würzburg. 相似文献
19.
Week-old wheat seedlings absorbed at least 40% NO 3− from NaNO 3 when preloaded with K + than when preloaded with Na + or Ca 2+. Cultures of Triticum vulgare L. cv. Arthur were grown for 5 days on 0.2 m m CaSO 4, pretreated for 48 hours with either 1 m m CaSO 4, K 2SO 4, or Na 2SO 4, and then transferred to 1 m m NaNO 3. All solutions contained 0.2 m m CaSO 4. Shoots of K +-preloaded plants accumulated three times more NO 3− than shoots of the other two treatments. Initially, the K +-preloaded plants contained 10-fold more malate than either Na +- or Ca 2+-preloaded seedlings. During the 48-hour treatment with NaNO 3, malate in both roots and shoots of the K +-preloaded seedlings decreased. Seedlings preloaded with K + reduced 25% more NO 3− than those preloaded with either Na + or Ca 2+. These experiments indicate that K + enhanced NO 3− uptake and reduction even though the absorption of K + and NO 3− were separated in time. Xylem exudate of K +-pretreated plants contained roughly equivalent concentrations of K + and NO 3−, but exudate from Na + and Ca 2+-pretreated plants contained two to four times more NO 3− than K +. Therefore K + is not an obligatory counterion for NO 3− transport in xylem. 相似文献
20.
Past research strongly indicates the importance of amino acids in the N economy of the Arctic tundra, but little is known about the seasonal dynamics of amino acids in tundra soils. We repeatedly sampled soils from tussock, shrub, and wet sedge tundra communities in the summers of 2000 and 2001 and extracted them with water (H 2O) and potassium sulfate (K 2SO 4) to determine the seasonal dynamics of soil amino acids, ammonium (NH 4+), nitrate (NO 3–), dissolved organic nitrogen (DON), dissolved organic carbon (DOC), and phosphate (PO 42–). In the H 2O extractions mean concentrations of total free amino acids (TFAA) were higher than NH 4+ in all soils but shrub. TFAA and NH 4+ were highest in wet sedge and tussock soils and lowest in shrub soil. The most predominant amino acids were alanine, arginine, glycine, serine, and threonine. None of the highest amino acids were significantly different than NH 4+ in any soil but shrub, in which NH 4+ was significantly higher than all of the highest individual amino acids. Mean NO 3– concentrations were not significantly different from mean TFAA and NH 4+ concentrations in any soil but tussock, where NO 3– was significantly higher than NH 4+. In all soils amino acid and NH 4+ concentrations dropped to barely detectable levels in the middle of July, suggesting intense competition for N at the height of the growing season. In all soils but tussock, amino acid and NH 4+ concentrations rebounded in August as the end of the Arctic growing season approached and plant N demand decreased. This pattern suggests that low N concentrations in tundra soils at the height of the growing season are likely the result of an increase in soil N uptake associated with the peak in plant growth, either directly by roots or indirectly by microbes fueled by increased root C inputs in mid-July. As N availability decreased in July, PO 42– concentrations in the K 2SO 4 extractions increased dramatically in all soils but shrub, where there was a comparable increase in PO 42– later in the growing season. Previous research suggests that these increases in PO 42– concentrations are due to the mineralization of organic phosphorus by phosphatase enzymes associated with soil microbes and plant roots, and that they may have been caused by an increase in organic P availability. 相似文献
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