摘要:

Barley (Hordeum vulgareL. cv. Martin) plants grown in solution culture, were exposed to increasing cadmium (Cd) concentration (0, 5, 10, 25, 50, and 100 μM) for a duration of 12 days. The sequence of important biochemical steps of nitrate (NO3) assimilation were studied in roots and shoots as a function of external Cd concentration. Cadmium uptake in roots and shoots increased gradually with Cd concentration in the medium. This Cd accumulation lowered substantially root and shoot biomass. The nitrate reductase (NR, EC 1.6.6.1) and nitrite reductase (NiR, EC 1.6.6.4) activities declined under Cd stress. Concurrently, tissue NO3contents and xylem sap NO3concentration were also decreased in Cd‐treated plants. These results suggest that Cd could exert an inhibitory effect on the assimilatory NO3reducing system (NR and NiR) through a restriction of NO3availability in the tissues. We therefore examined, in short‐term experiments (12 h), the impact of Cd on NO3uptake and the two reductases in nitrogen (N)‐starved plants that were pretreated or not with Cd. It was found that Cd induced inhibition of both NO3uptake and activities of NR and NiR, during NO3induction period. The possible mechanisms of Cd action on NO3uptake are proposed. Further, in Cd‐grown plants, the glutamine synthetase (GS, EC 6.3.1.2) showed a decreasing activity both in shoots and roots. However, increasing external Cd concentration resulted in a marked enhancement of glutamate dehydrogenase (NADH‐GDH, EC 1.4.1.2) activity, coupled with elevated levels of ammonium (NH4in tissues. On the other hand, the total protein content in Cd‐treated plants declined with a progressive and substantial increase of protease activity in the tissues. These findings indicate that under Cd stress the usual pathway of NH4assimilation (glutamine synthetase/glutamate synthase) can switch to an alternative one (glutamate dehydrogenase). The changes in all parameters investigated were concentration‐dependent and more marked in roots than shoots. The regulation of N absorption and assimilation by Cd in relation to growth and adaptation to stress conditions are discussed.

ISSN:0190-4167    

DOI:10.1080/01904169909365668

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Spring surface applications of15nitrogen (N)‐labeled urea were made in March 1995 and 1996 on one and two‐year‐old, field‐grown ‘Arapaho’ blackberry(RubussubgenusRubus)plants. Individual whole‐plant samples were collected at pre‐harvest (late May), post‐harvest (mid‐July), and early dormancy (late October). Plant parts separated for analysis were roots, primocanes, floricanes, primocane leaves, floricane leaves; and fruits. Soil samples were also taken from within the plant drip line at each sample date. Plant tissues were washed, dry weights measured, ground for acid digestion, total N determined, and15N analyzed. Plants collected in October had more total dry matter, with roots, primocanes, and primocane leaves contributing most to this total. Total N content decreased in all vegetative tissues (leaves and canes) from May to October. Compared to other plant tissues, floricane leaves and primocanes recovered significantly more fertilizer N in May while roots and primocane leaves contained more in October of each year. Floricanes and fruits did not increase in fertilizer N levels during the sampling period. Overall, the lowest percent fertilizer N recovery for whole plants was 12.8% for May 1995 and the highest was 32.4% for October 1996. Recovery of fertilizer N in the topsoil ranged from a low of 12.9% in October 1995 to a high of 38.6% in May 1996. There were no statistical differences in percent recovery of fertilizer N from topsoil among sample dates. Recovery of fertilizer N from subsoil in the October sample was much lower than that in May, probably due most to plant uptake, but also possibly to a downward movement out of the sample area by leaching or from other loss mechanisms. Averaging all sample dates, recovery was 59.5% in 1995 and 75.8% in 1996 for the plant and soil combined, with the remainder probably lost via volatilization, leaching, and/or denitrification.

ISSN:0190-4167    

DOI:10.1080/01904169909365669

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Plant genotypes within species differ widely in tolerance to excess manganese (Mn) that may occur in acid soils, or in neutral or alkaline soils having poor aeration caused by imperfect drainage or compaction. However, Mn tolerance mechanisms in plants are largely unknown. Silicon (Si) is reported to detoxify Mn within plants, presumably by preventing localized accumulations of Mn associated with lesions on leaves. Because Mn is paramagnetic, electron paramagnetic resonance (EPR) spectroscopy, shows promise as a tool for characterizing toxic and non‐toxic forms of Mn in tolerant and sensitive plants. The objective of our study was to use EPR to: i) determine the chemical/ physical state of Mn in Mn‐tolerant and ‐sensitive snapbean cultivars; and ii) characterize the protective effects of Si against Mn toxicity. Manganese‐sensitive Wonder Crop 2 (WC) and Mn‐tolerant Green Lord (GL) cultivars of snapbean were grown at pH 5.0, in a greenhouse, in a modified Steinberg solution containing: Mn=0.05mg.L‐1(optimal); Mn=1.0mgL‐1(toxic); Mn=1.0 mg L‐1plus Si=4 mg L‐1; and Mn=0.05 mg L‐1plus 4 mg Si L‐1. All trifoliate leaf samples exhibited a 6‐line EPR signal that is characteristic of hexaaquo Mn2+. In both cultivars, a higher EPR Mn2+signal‐intensity generally correlated with lower total leaf mass, higher total Mn concentrations and more pronounced symptoms of toxicity. Tolerance to excess Mn coincided with lower Mn2+signal intensity. Silicon treatments ameliorated Mn toxicity symptoms in both genotypes, decreased total leaf Mn concentrations, and decreased EPR Mn2+signal intensity. Results suggest that Mn toxicity is associated with reduced electron transport and accumulation of oxidation products in leaves. Amelioration of Mn toxicity by Si is regarded as connected with a reduction in this Mn‐induced process. Results indicated that EPR spectroscopy can be useful in investigating the biochemical basis for differential Mn tolerance in plants. The EPR observations might also help plant breeders in developing Mn‐tolerant cultivars.

ISSN:0190-4167    

DOI:10.1080/01904169909365670

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This greenhouse study aimed to analyze the impact of arbuscular mycorrhizal (AM) fungal associations on maize(Zea maysL. hybrid Pioneer 3905) in order to compare their functional compatibility and efficiency. The AM fungus species used for this study wereGlomus aggregatum, G. etunicatum, G. mosseae,andG. versiforme.Shoot and leaf masses, chlorophyll, soluble protein, total and reducing sugar, carbon (C), and nitrogen (N) concentrations, and glutamine synthetase (GS) activity in the maize leaves were analyzed. The root colonization ranged from 26% to 72% depending on the AM fungus species. Leaf mass was significantly higher when maize plants were colonized withG. etunicatumin comparison to the non‐AM control. The mycorrhizal effect on dry leaf mass ranged from 15.9% to 23.9% depending on the AM species. However, the total shoot mass did not differ significantly among the treatments. The mycorrhizal treatment had a marginally significant effect on the chlorophyll concentrations in maize leaves. The protein concentration was the highest in the plants colonized withG. etunicatumand the N percentage was significantly higher in the leaves of plants colonized byG. versiformeorG. aggregatumthan those withG. mosseae.However, the AM colonization did not significantly alter the GS activity among the treatments. The highest sugar concentrations were detected in the leaves of plants colonized byG. versiforme.The sugar concentrations as well as the C percentage were lower in the leaves of plants colonized byG. etunicatumcompared to the other mycorrhizal treatments but the values were comparable to the non‐AM control. Our overall results suggest that the expression of the mycorrhizal potential in the maize host plants varies among AM fungal species.

ISSN:0190-4167    

DOI:10.1080/01904169909365671

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Tomato plants(Lycopersicon esculentumMill. cv. Momotaro) were cultured in nutrient solution supplying 35 meq or 50 meq of nitrate (NO3) per plant weekly from the flowering stage of the first truss in two cropping seasons. The effects of NO3supply levels and cropping season on fruit growth of tomato were investigated. Furthermore, the relationship between the results of the plant sap analysis and fruit growth of tomato was analyzed. In the spring to summer cropping, NO3supplied was almost all absorbed and high productivity of tomato fruits was obtained in each treatment. In the fall to winter cropping, however, high NO3supply did not increase the uptake of NO3, but tended to decrease the rate of fruit set and marketable yield. Accumulation of NO3in the petiole sap was found with high NO3supply in the fall to winter cropping. Cropping season greatly influenced not only fruit growth but also the concentration of NO3in the petiole sap in relation to the ability of tomato plants to use available nitrogen (N). Furthermore, reduction in the rate of fruit set and weight of tomato fruit were found to relate to the low concentration of NO3in the petiole sap of the leaf just below this fruit truss. High NO3supply tended to increase potassium (K) concentration and electrical conductivity (EC) value, and to decrease phosphate (P), calcium (Ca), and magnesium (Mg) concentrations in the petiole sap. On the whole, concentrations of these elements in the petiole sap consistently reflected their uptake rates in two cropping seasons.

ISSN:0190-4167    

DOI:10.1080/01904169909365672

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Plant nitrogen (N) uptake, growth, and N use efficiency may be affected by N form (NO3‐or NH4+) available to the root. The objectives of this study were to determine the effect of mixed N form on dry matter production and partitioning, N uptake, and biomass N use efficiency defined as total dry matter produced per unit plant N (NUE1) in U.S. and tropical grain sorghums[Sorghum bicolor(L.) Moench]. The U.S. derived genotype CK 60 and three tropical genotypes, Malisor‐7, M 35–1, and S 34, were evaluated in a greenhouse trial using three nutrient solutions differing in their NO3‐/NH4+ratio (100/0, 75/25, 50/50). Shoot and root biomass, N accumulation, and NUE, were determined at 10‐leaf and boot stages. Averaged over all genotypes, shoot and root biomass decreased when NH4+concentration was increased in the solution. Shoot biomass was reduced by 11% for 75/25 and 26% for 50/50 ratios, as compared to 100/0 NO3‐/NH4+. Similarly, root biomass reduction was about 34% and 45% for the same ratios, respectively. Increasing NH4+concentration also altered biomass partitioning between shoot and root as indicated by decreasing root/shoot ratio. Total plant N content and NUE1were also reduced by mixed N source. Marked genotypic variability was found for tolerance to higher rates of NH4+. The tropical line M 35–1 was well adapted to either NO3‐as a sole source, or to an N source containing high amounts of NH4+. Such a characteristic may exist in some exotic lines and may be used to improve genotypes which do not do well in excessively wet soil conditions where N uptake can be reduced.

ISSN:0190-4167    

DOI:10.1080/01904169909365673

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

An estimated 30% of the world's arable soils are acidic and aluminum (Al) toxicity is often the primary growth‐limiting factor. Excess Al is especially undesirable in sub‐soils because it reduces rooting depth and branching and predisposes plants to drought injury. Liming the plow layer does not generally neutralize subsoil phytotoxicity and Al‐tolerant cultivars offer an alternative or supplemental solution to the problem. Genetic diversity for acid soil tolerance in alfalfa(Medicago sativaL.) is limited and a better understanding of the basic tolerance mechanisms would facilitate the design of more efficacious breeding procedures. Evidence is accumulating that organic acids and proteins elicited by Al stress may complex and detoxify Al either within, or external to, the root. Because Al is a paramagnetic element that can reduce T2 relaxation times (inter‐proton interactions) markedly, the mechanism of Al tolerance in alfalfa was investigated through T2‐based Magnetic Resonance Imaging (MRI) of young lateral root sections of an Al‐sensitive and an Al‐tolerant alfalfa clone grown in nutrient solution (0 or 111 μmol Al; pH 4.5). Root sections that developed under phytotoxic levels of Al accumulated considerable Al in the epidermis and internal root tissue. Aluminum may have been complexed by low molecular weight proteins and organic acids in the tolerant clone whereas the sensitive clone appeared to have abundant free Al; however, variation among replications indicates that free Al may still have been present in tolerant roots and that other tolerance mechanisms may also be important. Root buds accumulated little Al compared to the remainder of the root, indicating that the pronounced effects of Al on lateral root development are indirect. Magnetic Resonance Imaging images evaluated in this study provided clues to the basic mechanisms of Al tolerance in alfalfa and, with further refinement, could be used as one criterion for selecting Al‐tolerant plants.

ISSN:0190-4167    

DOI:10.1080/01904169909365674

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Neotyphodium coenophialum,(Morgan‐Jones & Gams) Glenn, Bacon & Hanlin, infected tall fescue (Festuca arundinaceaSchreb.) plants perform better than non‐infected isolines on phosphorus (P)‐deficient soils. Our objective was to characterize growth and P uptake dynamics of tall fescue in response to endophyte infection and P source at low P availability in soil. Two tall fescue genotypes (DN2 and DN4) infected with their naturally occurringN. coenophialumstrains (E+), and in noninfected (E‐) forms were grown in Lily soil (fine loamy siliceous, mesic Typic Hapludult) in a greenhouse for 20 weeks. Three soil P treatments were imposed: no P supplied (control) and P supplied as commercial fertilizer (PF) or as phosphate rock (PR) at the level of 25 mg P kg‐1soil. Interaction of tall fescue genotype and endophyte status had a significant influence on mineral element uptake suggesting high specificity of endophyte‐tall fescue associations. Endophyte infection did not affect root dry matter (DM) when no P was supplied but shoot DM was reduced by 20%. More biomass was produced and greater P uptake rate occurred in PR than PF treatment. Root DM was greater in E+ DN4 than E‐DN4 when supplied with either PF or PR. In contrast, endophyte infection did not affect root DM of DN2, regardless of P source. Relative growth rate (RGR) of E+ plants grown with PR was 16% greater than that of E‐plants. Endophyte infection did not improve growth or P uptake in PF treatment. When PR was supplied, P uptake rate was 24% greater in E+ DN2 than E‐ DN2, but endophyte infection did not benefit DN4. Phosphorus‐use efficiency was 6% less in E+ DN2 but 16% greater in E+ DN4 compared to E‐ plants, regardless of P source. Root exudates of E+ DN2, but not E+ DN4 solubilized more P from PR than those of E‐ plants. The correlation between root RGR and P uptake rate was relatively high for E‐ plants (r=0.76), but low for E+ plants (r=0.27) grown with PR. Results suggest that P uptake by E+ tall fescue might rely on mechanisms other than an increase in root biomass (surface area). Endophyte infection modified tall fescue responses to P source. This phenomenon was associated with modes of P acquisition which included enhanced activity of root exudates in releasing P from PR in E+ plants (DN2), and increased root biomass (DN4). The dominant means of P acquisition may be determined by a specific association of endophyte and tall fescue genomes. Endophyte‐tall fescue association plasticity contributes to widespread success of symbiotic in marginal resource conditions.

ISSN:0190-4167    

DOI:10.1080/01904169909365675

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

ISSN:0190-4167    

DOI:10.1080/01904169909365657

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor