共查询到20条相似文献,搜索用时 9 毫秒
1.
The short-lived radio-isotope nitrogen-13 (half-life 10 min)was used as a tracer in studying fluxes of N in the roots ofintact barley plants. After supplying the plants with 13N-nitratefor 30 min, efflux of 13N into an unlabelled (wash) solutionwas followed under steady-state conditions for a further 10min. Tests with ion exchange resins suggested that all of the13N released during this period was in the form of nitrate. In addition to nitrate from a surface film of solution and fromthe free space of the roots, efflux from another compartmentwas detected, tentatively identified as the cytoplasmic nitratepool. In plants grown with nitrate as the only external N-source,efflux from this compartment decreased with a rate constantabout 0·17 min1 (half-time 4 min). Adding ammoniumsulphate to the wash solution alone did not significantly affecteither the initial rate, or the rate constant, of efflux of13N from these roots. However, 13N efflux decreased more rapidly(rate constant about 0·32 min1, half-time 2·2min) in roots grown in, and subsequently washed with, solutioncontaining ammonium nitrate. In barley plants grown with 1·5 mol m3 nitrate,the cytoplasmic nitrate pool was estimated to contain about2% of the total nitrate in the roots, corresponding to a cytoplasmicnitrate concentration 26 mol m3. Nitrate efflux was equivalentto almost 40% of nitrate influx in the roots of these plants. Key words: Ion transport, nitrate, ammonium, efflux analysis, compartmentation 相似文献
2.
3.
Q10 values for 13NO3− influx were determined in `uninduced' (NO3−-starved) and `induced' (NO3−-pretreated) roots of barley (Hordeum vulgare L.) plants at various concentrations of external NO3− ([NO3−]0). At 0.02 mole per cubic meter [NO3−]0, Q10 values for influx were from 3 to 4 between 5 and 10°C. As [NO3−]0 increased Q10 values decreased, reaching values of 1.2 and 2.0, respectively, at 20 moles per cubic meter in uninduced and induced plants. The metabolic dependence of 13NO3− influx at low and high [NO3−]0 (0.1 and 20.0 moles per cubic meter, respectively) in uninduced and induced plants was probed by the use of various inhibitors. These experiments confirmed the findings of the Q10 studies, demonstrating that at low [NO3−]013NO3− influx was extremely sensitive to metabolic inhibition. By contrast, at high [NO3−]0, influx was relatively insensitive to the presence of inhibitors. 相似文献
4.
5.
Nutrient Supply and the Growth of the Seminal Root System in Barley: I. THE EFFECT OF NITRATE CONCENTRATION ON THE GROWTH OF AXES AND LATERALS 总被引:21,自引:3,他引:18
A method was devised by which different zones along a singleseminal axis of an intact plant could be exposed for extendedperiods to contrasting concentrations of nitrate (either 0.01or 1.0 mM) in continuous flow, the supply of all other nutrientsbeing favourable throughout. The concentration of nitrate wasfound to exert a direct and strictly localized effect upon thegrowth of lateral roots which, depending upon the supply ofassimilates from the shoot, resulted in marked modificationsto the form of the root system. Zones receiving 1.0 mM nitrateshowed an increase in the number and extension rate of bothfirst- and second-order laterals, associated with a preferentialaccumulation of dry matter, compared with zones in 0.01 mM nitrate.The average number of laterals (both first and second order)per cm of parent root was 4.4 in the presence of 1.0 mM nitrateand 2.2 in 0.01 mM. The average extension rates of first-orderlaterals were 0.61 and 0.26 cm d1 and second-order laterals,0.10 and 0.05 cm d1 for nitrate concentrations of 1.0and 0.01 mM respectively. The precise numbers and extensionrates of laterals in any one zone were affected, however, bythe rate of growth of laterals in other parts of the root system.In contrast, the extension rates of axes were little affectedby the concentration of nitrate to which their apical meristemswere exposed and approached 2.0 cm d1 provided the plantswere not nitrogen-starved. The significance of these resultsto the physiology of root growth and soil-plant relations isdiscussed. 相似文献
6.
1. An investigation was made into effect of daylength conditionsof the inhibition content of first-year seedlings of sycamore(Acer pseudoplatanus). 2. The shoot apical regions and mature leaves were extractedwith 80 per cent. Aqueous methanol, fractionated by paper chromatographyin isopropanol/ammonia and assayed by the wheat-coleptile growthtest. 3. A growth inhibitor was present in all extracts at Rf 0.7.Higher levels of inhibitor were present in both apices and matureleaves of plants transferred to short-day conditions than ofthose maintained under long-days throughout. 4. These difference in inhibitor level can be detected after25 days of short-day treatment, Preceding any markedeffect of daylength on growth. 5. Evidence is adduced in support of the hypothesis that theinhibitors is produced in the leaves during darkness and istransported to the apex during the photoperiod. 相似文献
7.
The Initial Uptake of Ions by Barley Roots: II. APPLICATION OF MEASUREMENTS ON SORPTION OF ANIONS TO ELUCIDATE THE STRUCTURE OF THE FREE SPACE 总被引:1,自引:0,他引:1
In previous experiments on excised barley roots, results werepresented showing the effect of varying the concentration ofthe uptake solution on the amount of anion which could subsequentlybe extracted in water. It was concluded that the system couldbe more satisfactorily analysed by means of the GoüyChapmanelectrical double-layer theory than by the Donnan theory. Onthe basis that ions diffuse into a system of negatively chargedpores within the root, the relationship between the quantityof water-extractable anion and its concentration in the uptakesolution has been examined in the light of the electrical double-layertheory. For potassium iodide and sulphate the experimental resultsconformed reasonably well with a structural model for the FreeSpace of parallel, charged surfaces separated by a mean distanceof about 200 A. The internal surface area of the free spacewas estimated as 2x106 cm2/g dry weight. The uptake of iodidefrom calcium iodide was somewhat greater than that predictedby the theory; this may be ascribed to interaction between theanions and divalent cations within the double layer. 相似文献
8.
The influence of protein synthesis and nitrate reductase activity on nitrate absorption by barley (Hordeum vulgare L.) was investigated. Cycloheximide decreased nitrate absorption. Pretreatment studies showed that cycloheximide affects either energy transfer or nitrate reductase activity or both. 相似文献
9.
10.
11.
光强对黄花菜植株生长效应的研究 总被引:9,自引:0,他引:9
研究结果表明,黄花菜植株能够在相对光照强度为12%-100%的条件下正常生长发育,且不影响经济产量。随着生境相对光强降低,植株花葶高度增加;单叶面积增大,单株叶片数量减少;总生物量增量减小;地上部分生物量与地下部分生物量的比值升高;光合速率日变化的居民较复杂。 相似文献
12.
1. A further study has been made of the effect of indole-3-acetic acid (auxin) on protoplasmic streaming in the epidermal cells of the Avena coleoptile. 2. The transient nature of the effect of auxin, both in accelerating and retarding streaming, is due to the temporary exhaustion of carbohydrate from the tissues. In presence of 1 per cent fructose or some other sugars the acceleration or retardation of streaming by auxin is not transient, but is maintained for at least 2 hours. 3. The retardation of streaming brought about by concentrations of auxin above 0.5 mg. per liter is due to oxygen deficiency This has been confirmed in several ways. 4. It follows that the effect of auxin is to increase the respiration of the coleoptile tissue. 5. Younger coleoptiles, 3 cm. long, are sensitive to lower concentrations of auxin than those 5 cm. long, and more readily exhibit oxygen deficiency as a result of the action of auxin. However, after decapitation their response to auxin more closely resembles that of 5 cm. coleoptiles. 6. The retardation of streaming in such coleoptiles, resulting from oxygen deficiency, is delayed by very dilute solutions of histidine. On this basis an explanation is suggested for the results of Fitting on streaming in Vallisneria leaves. 7. The mean rate of streaming in control untreated coleoptiles in pure water varies with the time of year, but not with the time of day. 8. The results support the view that auxin accelerates an oxygen-consuming process which controls the rate of protoplasmic streaming, and that the latter controls growth. The substrate for this process is probably sugar. 9. It is suggested that auxin also accelerates another oxygen-consuming process, which may withdraw oxygen from the process which controls streaming rate and hence cause retardation of the latter. 相似文献
13.
Theodore White 《The Journal of general physiology》1945,29(1):31-41
The estimation of the number of variables operating in cases of toxic action toward living organisms is discussed. The toxicity of glucose, sodium chloride, and copper nitrate solutions to Polycelis nigra has been investigated and also that of copper nitrate solutions whose osmotic pressure was adjusted to a constant level by the addition of glucose or of sodium chloride. It is shown that hypertonic solutions of copper nitrate are abnormally toxic but that the osmotic variable is not the factor responsible for this abnormally high toxicity. The lack of data which might elucidate such problems is indicated. During the course of this work it was observed that mixed solutions of copper nitrate + sodium chloride and copper nitrate + glucose exhibit toxicities greater than those expected from consideration of the separate toxicities of the components of the mixtures. 相似文献
14.
Transmembrane electrical potential differences (Δψ) of epidermal and cortical cells were measured in intact roots of barley (Hordeum vulgare L. cv Klondike). The effects of exogenous NO3− on Δψ (in the concentration range from 100 micromolar to 20 millimolar) were investigated to probe the mechanisms of nitrate uptake by the high-affinity (HATS) and low-affinity (LATS) transport systems for NO3− uptake. Both transport systems caused depolarization of Δψ, demonstrating that the LATS (like the HATS) for NO3− uptake is probably mediated by an electrogenic cation (H+?) cotransport system. Membrane depolarization by the HATS was “inducible” by NO3−, and saturable with respect to exogenous [NO3−]. By contrast, depolarization by the LATS was constitutive, and first-order in response to external [NO3−]. H+ fluxes, measured in 200 micromolar and in 5 millimolar Ca(NO3)2 solutions, failed to alkalinize external media as anticipated for a 2 H+:1 NO3− symport. However, switching from K2SO4 solutions (which were strongly acidifying) to KNO3 solutions at the same K+ concentration caused marked reductions in H+ efflux. These observations are consistent with NO3− uptake by the HATS and the LATS via 2 H+:1 NO3− symports. These observations establish that the HATS for nitrate uptake by barley roots is essentially similar to those reported for Lemna and Zea mays by earlier workers. There are, nevertheless, distinct differences between barley and corn in their quantitative responses to external NO3−. 相似文献
15.
Compartmental analyses of intact roots of barley (Hordeum vulgareL. cv. Klondike) plants, grown with different levels of NO3(up to 1·0 mol m3) in the external media, wereundertaken using 13NO3. Two additional treatments, namelysodium dodecyl sulphate (SDS) or brief exposure to high temperature,designed to investigate the identity of the three NO3compartments revealed by compartmental analyses, provided supportfor the identification of the latter as corresponding to superficialsolution, apoplasm, and cytoplasm. Half-lives for exchange ofthese compartments, 3 s, 30 s, and 7 mm, were unaffected bythe level of NO3 provided during growth. Independentestimates of 13NO3 fluxes obtained by direct methodsagreed well with values of fluxes calculated from the compartmentalanalyses. Cytoplasmic [NO3], estimated from the compartmental analyses,were in the range from 137 mol m3, and increasedwith increasing [NO3] of the medium. Such values forcytoplasmic [NO3] are inconsistent with an earlier proposal(Siddiqi, Glass, Ruth, and Rufty, 1990; Glass, Siddiqi, Ruth,and Rufty, 1990) of passive NO3 uptake in the concentrationrange above 10 mol m3. A model, based upon localizeddistribution of nitrate reductase activity in epidermal cells,is proposed in which the proposed passive low affinity NO uptakeat high external [NO3] is restricted to epidermal cells. During loading periods with 13NO3, significant amountsof 13N were translocated to the shoot. Two pools of 13N, onebeing the root symplasm, appear to participate in the transferof labelled N to the shoot. Key words: Barley, compartmentation, nitrate, nitrate reductase, 13N 相似文献
16.
Whole Plant Studies using Radioactive 13-Nitrogen: II. A COMPARTMENTAL MODEL FOR THE UPTAKE AND TRANSPORT OF NITRATE IONS BY Zea mays 总被引:1,自引:0,他引:1
Nitrate ion uptake by the roots of hydroponically grown maizeseedlings was measured using the short-lived isotope 13N. Itis shown to be described by a four compartment model, recognizablynitrogen in the root bathing solution, nitrogen which is readilyexchangeable from the root, nitrogen bound in the root, andnitrogen transported from the root. Some of the absorbed activity leaks back into the root bathingsolution with the efflux from the root, as a fraction of theinflux, increasing with concentration to be greater than 08at external nitrate ion concentrations above about 1.0 mol m3.The capacity of the exchangeable root pool increases with externalnitrate ion concentration, approaching the expected cytoplasmicnitrate ion content at the highest external nitrate ion concentrationsstudied (70 mol m3). The investigation has highlighted the problems of interpretinguptake profiles in experiments for which the 10 min half-lifeof 13N dictates experimental times that are comparable withthe times for saturation of root pools. Key words: Zea mays, 13N, Compartmental model, Nitrate uptake 相似文献
17.
Pepsin in solution is inactivated by the radiations (beta and gamma) from radium emanation. This chemical effect has been studied quantitatively. The principles involved in this radiochemical reaction are apparently the same as those found in the case of trypsin previously reported; namely, the change in the logarithm of the concentration of active enzyme varies directly with the variable, W. 相似文献
18.
19.