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1.
The influence of plant ontogeny on xylem exudate K+ concentrations and K+ transport to the shoot was studied in both nutrient-solution and field-grown tomato plants ( Lycopersicon esculentum ).
K+ concentrations in xylem exudate from decapitated plants decreased during tomato plant development from a high of 12 m M to a low of 5 m M . In the nutrient-solution plants, the most rapid decline occurred during the vegetative growth phase, while in field-grown plants, the xylem K+ concentrations remained high during an-thesis and then subsequently declined. The rapid decline in nutrient-solution plants might be related to a decrease in the absorptive efficiency of the root system. In field-grown plants, a reduction in the availability of assimilates to the root might account in part for the decrease in xylem exudate K+ concentrations. The volume (ml h−1 plant−1) and the net rates of K+ exudation (mmol h−1 plant−1) decreased dramatically as the fruits approached maturity. Since only a small reduction in xylem exudate K+ concentrations occurred during fruiting, the hydraulic conductivity of the root system decreased as the tomato plants aged. It is proposed that the ontogenetic changes in xylem transport of K+ contribute to a reduction in leaf free space K+ concentration which would explain the decline in tomato leaf K+ concentrations.  相似文献   

2.
Pb and Cd uptake in rice roots   总被引:9,自引:0,他引:9  
Pb and Cd are heavy metal pollutants that inhibit plant growth. Using a cultivated rice variety (Dongjin, Oryza sativa L.), we studied how the transport and toxicity of Pb2+ and Cd2+ are affected by the presence of K+, Ca2+ or Mg2+. K+ had a little effect on uptake or toxicity of Pb2+ and Cd2+. Ca2+ or Mg2+ blocked both Cd2+ transport into rice roots and Cd2+ toxicity on root growth, which suggested that their detoxification effect is directly related to their blocking of entry of the heavy metals. Similarly, Ca2+ blocked both Pb2+ transport into the root and Pb2+ toxicity on root growth. The protective effect of Ca2+ on Pb2+ toxicity may be related to its inhibition of the heavy metal accumulation in the root tip, a potential target site of Pb2+ toxicity. Mg2+ did not ameliorate the Pb2+ toxicity on root growth as much as Ca2+ did, although it decreased Pb2+ uptake into roots similarly as Ca2+ did. These results suggest that the protective effect of Ca2+ on Pb2+ toxicity may involve multiple mechanisms including competition at the entry level, and that Pb2+ and Cd2+ may compete with divalent cations for transport into roots of rice plants.  相似文献   

3.
The model presented takes into account the interaction between the negatively charged membranes and macromolecules and the cations. A central postulate is that a constant average surface charge density (σ) as well as a constant average surface potential (Ψ) is conserved under different ionic conditions. The model makes it possible to predict the size of σ and Ψ from measurements of Na, K, Mg and Ca content in plant tissues of the same age but grown under two different ionic conditions (e.g. high and low K+). Assumptions were made about the relative amounts of free and bound Ca2+ and σ and Ψ were calculated from values in the literature. In all cases σ (and Ψ) are predicted to be higher for shoot (−29 to −96 mC m−2) than for root membranes (−14 to −27 mC m−2). In most cases the predicted σ falls within the range determined experimentally for biological membranes.  相似文献   

4.
Heavy metal loads in forest soils have been increasing over time due to atmospheric inputs. Accumulation in the upper soil layers could affect establishment of seedlings and forest regeneration. Mediterranean species show a high initial root development, allowing seedlings to reach the moisture of deeper soil layers. In the present work seedlings of stone pine ( Pinus pinea L.) and maritime pine ( Pinus pinaster Ait.), were grown in culture solution supplied with 0.0, 0.1, 1 or 5 μ M CdSO4 or with 1 μ M CdSO4 and 1 μ M CuSO4 combined. In both species tap-root elongation was drastically reduced in the 5 μ M Cd2+ and in the (Cd2++ Cu2+) treatments. A supply of 0.1 or 1 μ M Cd2+, however, enhanced root elongation in Pinus pinea without significantly influencing root elongation in Pinus pinaster . In both species the root density (weight per unit length) and the width of the cortex increased in response to Cd2+ exposure. In Pinus pinaster the mitotic index decreased at the higher Cd2+ concentrations and when Cd2+ and Cu2+ were combined. The data suggest that cell elongation is more sensitive to Cd2+ than cell division. The number and length of the lateral roots were also affected by Cd2+ treatment to a higher degree in Pinus pinaster than in Pinus pinea, reflecting the different Cd- tolerance of the two species.  相似文献   

5.
Salt-tolerant reed plants ( Phragmites communis Trinius) and salt-sensitive rice plants ( Oryza sativa L. cv. Kinmaze) were grown in salinized nutrient solutions up to 50 m M NaCl, and growth, Na+ contents and kinetics of 22Na+ uptake and translocation were compared between the species to characterize the salt tolerance mechanisms operating in reed plants. When both plants were grown under the same salinity, Na+ contents of the shoots were lower in reed plants, although those of the roots were quite similar. The shoot base region of both species accumulated Na+ more than the leaf blades did. Sodium-22 uptake and pulse-chase experiments suggested that the lower Na+ transport rate from root to shoot could limit excessive Na+ accumulation in the reed shoot. There was a possibility that the apparently lower 22Na+ transport rate to the shoot of reed plants was due to net downward Na+ transport from shoot base to root.  相似文献   

6.
Rhizobial siderophore as an iron source for clover   总被引:1,自引:0,他引:1  
Iron uptake by clover plants ( Trifoliuin pratense L. cv. Hruszowska) was studied using radioactive ferric iron (55FeCl2). As shown by autoradiography of non-infected plants, purified rhizobial siderophore isolated from Rhizobium leguminosarum by, trifolii , stimulated the uptake and shoot transport of iron. Addition of rhizobial siderophore into the growth medium of nodulated clover did not affect the iron transport to the shoots. In the absence of the rhizobial siderophore, clover infected by either nitrogen-fixing (Nod Fix+) or nonfixing (Nod+ Fix) R. L. trifolii strains took up and transported into the shoots more iron than the non-infected control plants. Nodulated clover reduced Fe(III) more efficiently than the non-infected control plants.  相似文献   

7.
The surface charge density of wheat root membranes   总被引:1,自引:0,他引:1  
Seedlings of winter wheat ( Triticum aestivum L. cv. Hildur) were grown at 18°C for 7 days in darkness in a complete growth medium in the presence or absence of 1 m M KCl to produce roots with different ion contents (high and low K+ respectively). The roots were homogenized, the 3 000 g, 10 000 g, 30 000 g (further fractionated by two phase partitioning) and 100 000 g pellets isolated, and their surface charge densities (σ) determined by the use of 9-aminoacridine fluorescence. The average σ for all membrane fractions weighted for protein content was the same (−18 mC m−2) for low and high K+ roots. The K+, Na+, Mg2+ and Ca2+ content of roots was determined and used to calculate an average σ following the procedure of Bérczi et al. [Physiol. Plant. 61: 529–534 (1984)]. The predicted value (−11 mC m−2) does not deviate much from the experimentally determined value. It is concluded as a useful working hypothesis that the average surface charge density is constant and that the ionic content of plant cells is regulated such that the average surface potential is constant.  相似文献   

8.
Uptake and distribution of Ca+, Mg2+ and K2+ were investigated in plants of cucumber ( Cucumis sativus L. var. Cila) which had been cultivated for 12, 19, 32, or 53 days in complete nutrient solution with 1.0 m M Ca2+, 2.0 m M Mg2+ and 2.0 m M K+. The + concentration was about the same in roots and shoots, while the Ca2+ and Mg2+ concentrations were low in roots compared to shoots. The K+ concentration decreased with increasing leaf age, while the Ca2+ and Mg2+ concentrations increased, except in older plants with flowers and fruits, where an increased concentration was found in the youngest leaves. This is discussed in connection with increased indoleacetic acid (IAA) synthesis in the shoot. Excision of leaves at different levels from 21-day-old plants, followed by uptake for 24 h from the nutrient solution on days 22 and 23, resulted in no immediate reduction in Ca2+ (45Ca) uptake. Transport of Ca2+ increased to leaves above and below the excision point and total Ca2+ uptake remained at the same level as for the intact plant. It is suggested that regulation of Ca2+ uptake is primarily achieved in the root while the distribution in the shoot is regulated by the accessability of negative binding sites.  相似文献   

9.
Models for the regulation of K+ uptake in higher plant roots have become more complex as studies have moved from the level of excised low-salt roots to that of intact plants grown under fully autotrophic conditions. In this paper we suggest that some of the differences between the conditions are qualitative, possibly requiring fundamental changes to the model, rather than simply quantitative.
The uptake of K+ by low-salt roots of Zea mays L. [(A619 x Oh 43) x A632], was independent of Na+ concentration over a wide range. However, independence of Na+ was not the case in plants grown on complete nutrient medium in the light: inclusion of Na+ in the uptake medium enhanced K+ uptake. In the presence of Na+, K+ uptake rates were similar in whole plants with high root K+ contents to rates in excised or intact, low-salt roots.  相似文献   

10.
The photosynthate costs of processes (amino acid and protein synthesis and turnover, and pH regulation) associated with the utilization of nitrate (NO3), ammonium (NH4+) or glutamine (Gln) for plant growth were estimated. Based on these estimates, the effects of these forms of nitrogen (N) on the carbon balance of plants and on shoot–root biomass allocation were evaluated. The results indicated that NO3 as an N source for plant growth is not substantially more expensive to utilize than either NH4+ or Gln, particularly in the long term when costs due to protein turnover dominate the total costs of N utilization. It is also suggested that the photosynthate use in processes associated with N assimilation has little impact on the carbon balance of plants, and hence on shoot–root biomass allocation.  相似文献   

11.
The effect of Zn2+ on the plasma membrane permeability and superoxide radical (O2-) formation in roots was studied with cotton ( Gossypium hirsutum L. cv. Delta-pine 15/21) plants grown in nutrient solution with different Zn2+ supply. Compared to Zn-sufficient plants, the plasma membrane permeability of Zn-deficient plants was increased as indicated by a 3-, 5- and 2.5-fold increase in root cell leakage of K+, NO3- and organic carbon compounds, respectively. Resupply of Zn2+ to Zn-deficient plants for 12 h substantially decreased this leakage. The effects of Zn2+ on membrane permeability were closely correlated with the levels of O2- measured by electron spin resonance (ESR) spectroscopy in the microsomal membrane fraction and in the cytosol fraction of root cells. The amplitudes of the O2- -derived Tiron ESR signal also coincided with a O2- -generating oxidase activity which was strongly dependent on the presence of NADPH and FAD. The results suggest that Zn2+ directly affects the integrity of the plasma membrane, at least in part, by interfering with O2- generation by a membrane-bound NADPH oxidase.  相似文献   

12.
Uptake and translocation of calcium in cucumber   总被引:1,自引:0,他引:1  
Uptake and translocation of Ca2+(45Ca) were compared with water translocation in 12-day old intact plants and excised roots of cucumber ( Cucumis sativus L. var. Cilla), which had been cultivated in nutrient solution. No immediate reduction of Ca2+ uptake was found when water translocation was reduced by excision of the shoot. In the presence of 2,4-dinitrophenol Ca2+ translocation was reduced in the intact plants while water translocation was unchanged. It is suggested that regulation of Ca2+ uptake is primarily achieved in the root. The DNP-sensitive mechanism of Ca2+ uptake was associated with the root and probably represented transport through the endodermis into the stele.  相似文献   

13.
Mechanism of iron uptake by plants   总被引:5,自引:0,他引:5  
Abstract. Green plants require a continuous supply of Fe as they grow, because Fe does not not move from the older to the newer leaves. Soils do not lack Fe per se , but it may not be available to plants grown in alkaline soils. Plants are classed 'Fe-efficient' if they respond to Fe-deficiency stress by inducing biochemical reactions that make Fe available in a useful form, and 'Fe-inefficienT' if they do not. Iron uptake induced in response to Fe stress involves release of hydrogen ions and reductants by the root. The lowered pH and presence of reductant at the root zone, along with reduction of Fe3+ to Fe2+ at the root surface, enables Fe2+ to be taken up primarily through the young lateral roots. Ferrous iron is present throughout the protozylem and may or may not have entered the root by a carrier. The root-absorbed Fe2+ is oxidized to Fe3+ at the junction of the protoxylem and the metaxylem, chelated by citrate, and then transported in the metaxylem to the plant top. In the plant, the chemical reactions injuced by Fe-deficiency stress may affect nitrate reductase activity, use of Fe from Fe3+ phosphate and chelating agents, and tolerance to heavy metals. An efficient mechanism for Fe uptake in roots appears to be important for the efficient use of Fe in plant tops.  相似文献   

14.
Vitamin D3 and stigmasterol have been previously shown to stimulate growth, Ca2+ fluxes and calmodulin synthesis in Phaseolus vulgaris roots. In this study, these sterols (10−9 M ) were shown to accelerate the incorporation of [3H]-thymidine into DNA in Phaseolus vulgaris (L. cv. Contraancha) root apices, similarly to a mixture of the mitogenic plant growth factors 2,4-dichlorophenoxyacetic acid and kinetin (4.6 μ M each). The effects of stigmasterol were blocked by flufenazine, a calmodulin antagonist. Analogously to stigmasterol, the plant hormones stimulated calmodulin synthesis as shown by double labeling of root proteins with [14C]-leucine and [3H]-leucine, respectively, followed by their separation on sodium dodecyl sulfate-po-lyacrylamide gels and a calmodulin affinity column, immunoblot analysis and cyclic AMP phosphodiesterase activation assays. The stimulation of root calmodulin formation by stigmasterol was abolished in the absence of Ca2+ in the incubation medium and was mimicked by the Ca2+ ionophore A–23187. The results suggest that the sterols, like plant mitogenic hormones, promote DNA synthesis, and that these compounds stimulate calmodulin synthesis as a consequence of their mitogenic activity. Ca2+ appears to mediate the action of the sterols.  相似文献   

15.
Root zone calcium modulates the response of potato plants to heat stress   总被引:1,自引:0,他引:1  
Potato plant growth and development are known to be severely impacted by heat stress. Here plants grown in a chemically inert medium of 1 : 1 quartzite : perlite (v : v) were subjected to either 35/25°C (stress) or 20/15°C (control) day/night air temperatures and four concentrations of root zone calcium (5, 25, 125 and 600 µ M Ca) for 3 weeks. We report for the first time that potato plant growth under heat stress can persist at specific levels of Ca2+ in the root zone and that the Ca2+ level required for growth under heat stress exceeds that required for growth under normal temperatures. We also provide strong, initial evidence that the ability of high Ca2+ levels to mitigate heat stress effects results from shifts in meristematic activity. Total foliar mass and leaf area were essentially unaffected by Ca2+ level under control temperatures. Under heat stress, leaf area was reduced to about 5% of the control at 5 and 25 µ M Ca but to only 70% of the control at 125 and 600 µ M Ca. Likewise, total foliar mass was reduced under heat stress to about 30% of the control at 5 and 25 µ M Ca but total foliar mass was greater under heat stress than control conditions at 125 and 600 µ M Ca. This increase at higher Ca2+ concentrations was due primarily to axillary shoot growth. Anatomical studies of leaves grown under heat stress show that cell expansion was impaired by heat stress and this impairment was overcome by increasing root zone calcium levels. These results provide insight into the mechanism by which root zone Ca2+ may modulate plant response to heat stress.  相似文献   

16.
Dehydrins are hydrophilic proteins that accumulate during embryogenesis and osmotic stress responses in plants. Here, we report an interaction between citrus dehydrin Citrus unshiu cold-regulated 15 kDa protein (CuCOR15) and DNA. Binding of CuCOR15 to DNA was detected by an electrophoretic mobility shift assay, a filter-binding assay and Southwestern blotting. The binding was stimulated by physiological concentrations of Zn2+, but little stimulation occurred when other divalent cations, such as Mg2+, Ca2+, Mn2+, Ni2+ and Cu2+, were substituted for Zn2+. Ethylenediaminetetraacetic acid cancelled the Zn2+-stimulated binding. A binding curve and competitor experiments suggested that the DNA binding of CuCOR15 exhibited low affinity and non-specificity. Moreover, tRNA competed with the DNA binding. Histidine-rich domains and a polylysine segment-containing domain participated in the DNA binding. These results suggest that CuCOR15 can interact with DNA, and also RNA, in the presence of Zn2+. Dehydrin may protect nucleic acids in plant cells during seed maturation and stress responses.  相似文献   

17.
Development of salt-tolerant genotypes is central both to remediation of salinity-affected land and to meet increasing global food demand, which has been driving expansion of cropping into marginal areas. The bottleneck of any breeding programme is the lack of a reliable screening technique. This study tested the hypothesis that the ability of plants to retain K+ under saline conditions is central to their salt tolerance. Using seven barley cultivars contrasting in salt tolerance (CM72, Numar, ZUG293, ZUG95, Franklin, Gairdner, ZUG403), a comprehensive study was undertaken of whole-plant (growth rate, biomass, net CO2 assimilation, chlorophyll fluorescence, root and leaf elemental and water content) and cellular (net fluxes of H+, K+, Na+ and Ca2+) responses to various concentrations of NaCl (20–320 m m ). Na+ selective microelectrodes were found to be unsuitable for screening purposes because of non-ideal selectivity of the commercially available Na+ LIX. At the same time, our results show very strong negative correlation between the magnitude of K+ efflux from the root and salt tolerance of a particular cultivar. K+ efflux from the mature root zone of intact 3-day-old seedlings following 40 min pretreatment with 80 m m NaCl was found to be a reliable screening indicator for salinity tolerance in barley. As a faster and more cost-effective alternative to microelectrode measurements, a procedure was developed enabling rapid screening of large numbers of seedlings, based on amount of K+ leaked from plant roots after exposure to NaCl.  相似文献   

18.
Soybean root and nodule nitrate reductase   总被引:5,自引:0,他引:5  
Nitrate reductase (NR) activity was followed in root and nodule from Glycine max (L.) Merr. (Cv. Tracy) inoculated with Rhizobium japonicum . Initially, a plus NO3- in vivo assay was used. When chlorate-resistant mutants were used as inoculum, nodule NR activity was reduced by about 90%. indicating that the bacteroid accounts for much of the normal nodule's NR. With plants 3 to 15 weeks of age nodule NR activity (g fresh weight)-1 was highest in young plants and root activity highest in old plants. Root and nodule total NR activity increased with plant age and were often not greatly different. Root NR activity correlated with plant NO3- supply and increased from 0.8 to 11.4 μmol plant-1 h-1 as NO3- was increased from 0 to 3 m M . In contrast, nodule NR activity was high in plants grown without NO3- and did not appear to increase as nitrate supply to the plant was increased. Nodule activity was 6 to 14 μmol NO2- plant-1 h-1. Use of a minus NO3- in vivo assay had little affect on root NR activity, but greatly reduced nodule activity. Root tissue was found to have 5 to 38 times more NO3- than nodule tissue. It is concluded that low nitrate levels within the nodule limit NR activity and that it is improbable that the nodule is a major site of plant nitrate reduction.  相似文献   

19.
Six cultivars of barley ( Hordeum vulgare L., cvs Salve, Nürnberg II, Bomi, Risø 1508, Mona and Sv 73 608) were exposed for three weeks to combinations of high and low mineral supply and differential root/shoot temperature. For all the parameters tested [fresh and dry weights, contents and levels of N, K+, Ca2+ and Mg2+, and influx of Rb+(86Rb)] the cultivar differences were influenced by the mineral supply, the root temperature and the age of the plants.
The cultivar differences in N nutrition of three-week-old plants could partly be attributed to variation in root size, uptake of N and in use-efficiency of the element. The cultivar variation in root-shoot partitioning of N was small, except when low mineral supply was combined with a low root temperature. Similarly, cultivar differences in contents of K+, Ca2+ and Mg2+ were influenced by variation in uptake, use-efficiency and root/shoot partitioning of the elements. Low root temperature increased cultivar variation in K+, Ca2+ and Mg2+ partitioning.
The modern cultivar Salve was compared with Nürnberg II, which is derived from a German land race. Nürnberg II performed better than Salve when low root temperature and restricted mineral supply were combined. Otherwise Salve grew better, partly due to a more efficient use of N.
Two high-lysine lines, Risø 1508 and Sv 73 608, were compared with their mother lines Bomi and Mona. The differences obtained revealed no general effect of the high-lysine genes on growth and mineral nutrition of up to three-week-old barley plants.  相似文献   

20.
The fix-2 mutant of Rhizobium meliloti affected in the invasion of alfalfa root nodules (Inf/Fix) is K+ sensitive and unable to adapt to alkaline pH in the presence of K+. Using directed Tn 5 mutagenesis, we delimited a 6 kb genomic region in which mutations resulted in both Inf/Fix and K+-sensitive phenotypes. In this DNA region, seven open reading frames (ORFs) were identified and the corresponding genes were designated phaA , B , C , D , E , F and G . The putative PhaABC proteins exhibit homology to the subunits of a Na+/H+ antiporter from an alkalophilic Bacillus strain. Moreover, PhaA and PhaD also show similarity to the ND5 and ND4 subunits of the proton-pumping NADH:ubiquinone oxidoreductase respectively. Computer analysis suggests that all seven proteins are highly hydrophobic with several possible transmembrane domains. Some of these domains were confirmed by generating active alkaline phosphatase fusions. Ion transport studies on phaA mutant cells revealed a defect in K+ efflux at alkaline pH after the addition of a membrane-permeable amine. These results suggest that the pha genes of R. meliloti encode for a novel type of K+ efflux system that is involved in pH adaptation and is required for the adaptation to the altered environment inside the plant.  相似文献   

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