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1.
Phloem translocation of photoassimilates between source andsink is considered to be linked with active retrieval of sugarsleaked to the vascular apoplast. This hypothesis was evaluatedby studying photo-assimilate movement in petioles of intactplants of Cyclamen persicum and Primula obconica in the presenceof inhibitors affecting sucrose retrieval (PCMBS, CCCP). Inhibitorsolutions were applied by rinsing locally isolated petiole bundlesor by injection into the petioe parenchyma. PCMBS and CCCP reduced[14C]sucrose retrieval from the petiole apoplast by the vascularcells and altered the distribution pattern of 14C-photoassimilateswithin the petiole tissues. However, these treatments did notaffect translocation through the petiole phloem. Evidence isprovided that the reagents were present in the vascular apoplastsurrounding the translocating phloem. It was concluded thatassimilate movement in the petiole of Cyclamen and Primula wasindependent of apoplastic retrieval. Key words: Cyclamen, Primula, phloem, transport, path, sucrose, retrieval 相似文献
2.
Phloem Loading in Coleus blumei in the Absence of Carrier-Mediated Uptake of Export Sugar from the Apoplast 总被引:7,自引:4,他引:3 下载免费PDF全文
Phloem loading in Coleus blumei Benth. leaves cannot be explained by carrier-mediated transport of export sugar from the apoplast into the sieve element-companion cell complex, the mechanism by which sucrose is thought to load in other species that have been studied in detail. Uptake profiles of the export sugars sucrose, raffinose, and stachyose into leaf discs were composed of two components, one saturable and the other not. Saturable (carrier-mediated) uptake of all three sugars was almost completely eliminated by the inhibitor p-chloromercuribenzenesulfonic acid (PCMBS). However, when PCMBS was introduced by transpiration into mature leaves it did not prevent accumulation of 14C-photosynthate in minor veins or translocation of labeled photosynthate from green to nonchlorophyllous regions of the leaf following exposure to 14CO2. The efficacy of introducing inhibitor solutions in the transpiration stream was proven by observing saffranin O and calcofluor white movement in the minor veins and leaf apoplast. PCMBS introduced by transpiration completely inhibited phloem loading in tobacco leaves. Phloem loading in C. blumei was also studied in plasmolysis experiments. The carbohydrate content of leaves was lowered by keeping plants in the dark and then increased by exposing them to light. The solute level of intermediary cells increased in the light (phloem loading) in both PCMBS-treated and control tissues. A mechanism of symplastic phloem loading is proposed for species that translocate the raffinose series of oligosaccharides. 相似文献
3.
Phloem Loading and Transport of Endogenously or Exogenously Labelled Photo-Assimilate in Bean, Beet, Maize and Cucurbit 总被引:1,自引:0,他引:1
Transport of carbon-11 labelled photo-assimilate was monitoredin Phaseolus vulgaris. Beta vulgaris, Zea mays, and Cucwbitopepo. The region of leaf to be labelled was first abraded anda solution passed over it to gain access to its apoplast andmonitor changes in label therein. With PCMBS in the bathingsolution the rate of washout of label into the bathing solutionincreased, but the effect of phloem loading was very variablefor each species: on some occasions transport was hardly affected,on others it was halted. This was true even for Cucurbito pepo,where a symplastic pathway of loading has been widely acceptedand suggests that PCMBS affects symplastic transport or thatthere is an apoplastic step in Cucurbito pepo. Apoplastic pHhad little effect on transport or label washout unless a veryacid (pH 40) buffer was introduced, contrary to notions of hydrogenion co-transport for sugar uptake. Anoxia caused phloem loadingto decrease immediately and label washout to increase in allspecies. It is suggested that both symplastic and apoplasticpathways can operate in all species but that their proportionvaries according to species and ambient and/or growth conditions. Key words: Phloem loading, photo-assimilate transport 相似文献
4.
GRUSAK MICHAEL A.; DELROT SERGE; NTSIKA GASPARD 《Journal of experimental botany》1990,41(11):1371-1377
Petiole heat-girdle treatments (followed by a 5 min 14CO2 assimilation)were performed on mature leaves of Vicia faba, in order to assesstheir effect on the partitioning of photo-assimilates to theminor vein phloem. Whole leaf autoradiographic evidence indicateda high leaf-to-leaf variation in the image intensity over theminor veins (relative to the mesophyll/epidermal background)in both control and heat-girdled groups of leaves. The averagedegree of minor vein labelling in heat-girdled leaves, however,was found to be significantly lower than that in controls. Comparativeassessment of vein labelling was based on microscopic densityreadings of silver grains over veinal and interveinal regionsin autoradiographic images. Investigations into the cause ofthis alteration in vein labelling indicated no involvement ofan inhibition of apoplasmic phloem loading, as both heat-girdledand control leaves of Vicia were shown to have comparable minorvein uptake of exogenously supplied 14C-sucrose. Heat-girdlingwas shown, however, to increase significantly the partitioningof recently fixed carbon into the insoluble (mainly starch)fraction relative to the ethanol-soluble fraction, within 12min of the treatment. We suggest that this carbon partitioningchange can primarily account for the change in vein labelling,since an increase in the insoluble fraction would result in(1) more 14C-activity remaining in the leaf mesophyll and (2)less 14C-activity going into the mesophyll export pool, andthus, less 14C-sucrose being transferred to the minor vein region.Additionally, although leaf export was completely halted inheat-girdled leaves, 14C-activity was found within the majorveins as far as the point of petiole heat-girdling (followinga 5 min assimilation and 4 h chase). Apparently, continued (butlimited) solution flow within the sieve elements is maintainedby transport pathway unloading within the treated leaves. Key words: Phloem loading, carbon partitioning, heat-girdle, Vicia faba 相似文献
5.
Changes in phloem loading rate were inferred from observationsof 11C export from attached leaves of C3 and C4 monocots anddicots. Loading decreased under anoxia in C3 leaves, but notin general in the leaves of either C4 monocots or dicots inthe light. However, loading rate in the C4 leaves did reduceif the leaf was also darkened or received no CO2. We suggestthat insensitivity to anoxia in C4 leaves is due to oxygen fromphotosynthesis which is retained in the bundle sheath at a concentrationsufficient to energize a phloem loading system. There may alsobe another system which is insensitive to anoxia since the effectsof shade and CO2 deprivation were not always seen, and loadingwas not completely stopped by these treatments. Key words: Phloem loading, C3, C4 相似文献
6.
A three-step screening method was developed to identify the mode of phloem loading in intact leaves. Phloem loading of 14CO2-derived photosynthate was challenged by p-chloromercuribenzenesulfonic acid (PCMBS) in leaves of dicotyledons with either a symplasmic (type 1, with intermediary cells as companion cells) or apoplasmic (type 2b, with transfer cells as companion cells) minor-vein configuration. Firstly, photosynthate export as the result of phloem loading was measured by collection of phloem exudate from the petiole. The PCMBS had virtually no effect on photosynthate export in representatives of type-1 families (Lamiaceae, Lythraceae, Onagraceae, Saxifragaceae). In contrast, photosynthate export was strongly reduced by PCMBS in representatives of type-2b families (Asteraceae, Balsaminaceae, Dipsacaceae, Linaceae, Tropaeolaceae, Valerianaceae) and type-2b members of polytypical families (Fabaceae, Scrophulariaceae). Secondly, densitometric measurements of leaf autoradiographs demonstrated that the contrast between the mesophyll and the lower-order veins was hardly affected by PCMBS treatment in type-1 species, whereas PCMBS strongly reduced the contrast in type-2b species. Thirdly, separate 14C-radioassays of vein and mesophyll tissues confirmed this observation. The three-step procedure thus revealed a strong and consistent reduction of phloem loading by PCMBS in type-2b species which was absent in type-1 species. In conclusion, phloem loading in type-2b species occurs via the apoplast and type-1 species execute an alternative — most likely symplasmic — mode of phloem loading.Abbreviations PCMBS
p-chloromercuribenzenesulfonic acid
- SE/CC-complex
sieve element/companion cell complex
We gratefully acknowledge the expert help of Dr. Maarten Terlou, Department of Image Processing and Design, University of Utrecht, in carrying out the densitometric measurements. 相似文献
7.
Cellular plasmolysis with l M solutions of mannitol appearedto sever plasmodesmatal interconnections between all cells ofthe stems of Phaseolus vulgaris plants except the sieve element-companioncell (secc) complexes. Phloem loading and uptake of [14C]sucroseby the storage cells of the stems was unimpaired by cellularplasmolysis followed by rehydration of the stem tissues. Accumulationof phloem-transported 14C-photosynthates of the treated stemswas inhibited in summer-grown plants and unaffected in winter-grownplants indicating that phloem unloading follows a symplasticand a free-space route respectively depending on growth season.At a concentration that did not interfere with cellular metabolism,p-chloromercuribenzene sulphonic acid (PCMBS) applied to thestems blocked [14C]sucrose loading into the phloem and storagecells of the stem, but had no effect on the pool size of free-spacesugars. This latter response is consistent with a facilitatedmechanism of sugar unloading to the stem free-space. Accumulationof phloem-transported 14C-photosynthates was stimulated by PCMBSand this effect was most pronounced in winter-grown plants.Cellular plasmolysis followed by rehydration abolished the PCMBSaction on 14C-photosynthate accumulation. This effect is consistentwith a PCMBS induction of phloem unloading through the stemsymplast. It is proposed that phloem unloading in bean stemsmay follow either a free-space or symplastic route and thatthe latter route is entrained under sink-limited conditions. Phaseolus vulgaris, french bean, stem, phioem unloading, free-space, symplast 相似文献
8.
The Effect of Calcium Starvation on Assimilate Partitioning and Mineral Distribution of the Phloem 总被引:1,自引:0,他引:1
Populus plants were grown in a medium lacking calcium and exposedto 14CO2. In contrast to plants in the complete nutrient medium,the percentage amount of 14C-assimilates increased in the leavesof calcium-deficient plants and decreased in the stem and theroots. When plants were grown without potassium or magnesiumno differences in the amount of 14C-label occurred in comparisonwith plants in the complete nutrient medium. Translocation wasrecorded by microautoradiography. It was observed that considerableamounts of labelled photoassimilates were unloaded from thephloem in the middle part of the stem in plants of the completenutrient medium. In contrast, during calcium starvation 14C-labelwas restricted to the phloem of the stem. In addition, the concentrationsof magnesium and phosphorus showed a remarkable increase instem sieve tubes of calcium-deficient plants. When sieve tubesof source leaves from Populus, barley and maize were comparedwith those of sink leaves, the latter showed higher calciumconcentrations. The results suggest that calcium is a necessaryfactor in the regulation of phloem translocation. Key words: Calcium deficiency, phloem translocation, sieve element loading and unloading, X-ray microanalysis 相似文献
9.
Assimilation of gaseous ammonia and the transport of its products in barley and spinach leaves 总被引:2,自引:0,他引:2
The interactions between the assimilation and transport of nitrogenand carbon were investigated in barley and spinach leaves. Bothplants were fumigated with NH3 (1 mg m3 and the contentof amino acids, sucrose and carbon intermediates of amino acidmetabolism were analysed in the leaves, apoplast and phloemsap. The following changes took place in the C- and N-metabolismof barley leaves during 5 h of fumigation with NH3 (a) The contentsof amino acids, especially glutamine, largely increased andthe contents of sucrose, 2-oxoglutarate, phosphoenolpyruvate,and glycerate-3-phosphate declined. (b) A decrease in the phophoenolpyruvatecontent was accompanied by an increased activity of phosphoenolpyruvatecarboxylase. (c) The altered cytosolic concentrations of aminoacids and sucrose during NH3 fumigation correlated with similarchanges in the apoplast and phloem sap. The altered percentageof each amino acid relative to the total amino acid concentrationin the cytosol, caused by NH3 fumigation, is reflected in theapoplast and the phloem sap. The results indicate that the concentrations of amino acids in the cytosol determine their concentrationsin the phloem. Key words: Amino acids, ammonia fumigation, barley leaves, C: N partitioning, phosphoenolpyruvate carboxylase, phloem sap, spinach leaves 相似文献
10.
Hordeum vulgare cv. California Mariout was grown for 50 d insand culture at 100 mol m3 NaCl. Xylem sap was collectedthrough incisions at the base of individual leaves along thestem axis by applying pressure to the root system. K+ concentrationsin the xylem sap reaching individual leaves increased towardsthe apex, while concentrations of Na+, NO3, and Cldeclined. Phloem exudate was obtained by collecting into Li2EDTAfrom the base of excised leaves. K/Na ratios of phloem exudatesincreased from older to younger leaves. K/Na ratios in xylem sap and phloem exudate were combined withchanges in ion content between two harvests (38 and 45 d aftergermination) and the direction of phloem export from individualleaves, to construct an empirical model of K+ and Na+ net flowswithin the xylem and phloem of the whole plant. This model indicatesthat in old leaves, phloem export of K+ greatly exceeded xylemimport. In contrast, Na+ export was small compared to importand Na+ once imported was retained within the leaf. The direction of export strongly depended on leaf age. Old,basal leaves preferentially supplied the root, and most of theK+ retranslocated to the roots was transferred to the xylemand subsequently became available to the shoot. Upper leavesexported to the apex. Young organs were supplied by xylem andphloem, with the xylem preferentially delivering Na+ , and thephloem most of the K+ . For the young ear, which was still coveredby the sheath of the flag leaf, our calculation predicts phloemimport of ions to such an extent that the surplus must havebeen removed by an outward flow in the xylem. Within the culm,indications for specific transfers of K+ and Na+ between xylemand phloem and release or absorption of these ions by the tissuewere obtained. The sum of these processes in stem internodes and leaves ledto a non-uniform distribution of Na+ and K+ within the shoot,Na+ being retained in old leaves and basal stem internodes,and K+ being available for growth and expansion of young tissues. Key words: Hordeum vulgare L., K+, Na+, stem, salt stress 相似文献
11.
Zinc Mobility in Wheat: Uptake and Distribution of Zinc Applied to Leaves or Roots 总被引:12,自引:1,他引:12
Little is known about transport of Zn from leaves to other plantorgans. The present study tested a range of Zn forms appliedfoliarly for their suitability to provide adequate Zn nutritionto wheat (Triticum aestivum L.). Transport of65Zn applied eitherto leaves or to one side of the root system was also studied.Inorganic (ZnO, ZnSO4) and chelated sources of Zn (ZnEDTA, glycine-chelatedBiomin Zn) applied foliarly provided sufficient Zn for vigorousgrowth. Zinc concentrations in roots and shoots were in thesufficiency range, except in the -Zn control. Foliar treatmentswith ZnSO4and chelated Zn forms resulted in shoot Zn concentrationsin 7-week-old plants being about two-fold greater than thosein plants supplied with Zn in the root environment or via foliarspray of ZnO. Adding surfactant to foliar sprays containingchelated forms of Zn did not cause negative growth effects,but surfactant added to ZnO or ZnSO4foliar sprays decreasedshoot growth. Adding urea to the ZnO foliar spray had no effecton shoot growth. Foliarly-applied65Zn was translocated to leavesabove and below the treated leaf as well as to the root tips.Stem girdling confirmed that65Zn transport toward lower leavesand roots was via the phloem. Split-root experiments showedintensive accumulation of65Zn in the stem and transport to allleaves as well as to the root tips in the non-labelled sideof the root system. Foliar application of Zn in inorganic ororganic form is equally suitable for providing adequate Zn nutritionto wheat. Phloem transport of Zn from leaves to roots was demonstrated.Copyright 2001 Annals of Botany Company Foliar spraying, phloem, surfactant, urea, xylem, wheat, zinc 相似文献
12.
Mhling K.H.; Plieth C.; Hansen U-P.; Sattelmacher B. 《Journal of experimental botany》1995,46(4):377-382
The fluorochrome FITC-dextran was used to measure the effectof light on the apoplastic pH of intact Vicia faba leaves withthe ratio imaging technique. In darkadapted leaves the apoplasticpH varied depending on the leaf between 5.2 and 5.9. Red light(660 nm, 412 W m2) leads to multiphasic responses:in the first seconds an alkalinization ({small tilde}0.3 pHunits), and thereafter an acidification of the leaf apoplast({small tilde}0.4 pH units) were observed. Both effects couldbe inhibited by DCMU. While variation of CO2 concentration revealedno effect on light-induced apoplastic pH changes, a decreasein O2 concentration decreased the effect. On the basis of ourdata it is suggested that the influence of photosynthesis onplasmalemma H+ ATPase is responsible for the observed effects,rather than altered CO2 uptake. Key words: Leaf apoplast, apoplastic pH, light, ratio imaging, pH-sensitive fluorescent dye, Vicia fab 相似文献
13.
To test for the existence of an apoplastic unloading/reloadingstep in phloem translocation, as envisaged in the relay hypothesisof phloem transport, isotopic trapping experiments were performedon Ricinus comunis L. var. Gibsonii. A CO2 buffer system wasused to supply 14CO2 at constant partial pressure and constantspecific activity to a photosynthesizing leaf. The subtendinginternode was perfused with solutions of sugars or of mannitoland transolation of 14C past the perfused zone was monitoredby the collection of phloem exudate. Trapping of activity inthe perfusate was enhanced by the presence of sugars as wouldbe expected with an unloading/reloading process. However, therewas no evidence that introduction of the unlabelled sugars tothe apoplast also reduced activity in the phloem exudate. Moreover,the rate of loss of activity to the perfusing solutions representedonly 1% of the rate of appearance in the exudation. It is suggestedthat the trapping results may reflect an unloading of tracerfrom the phloem associated with a subsequent reloading by adjacenttissues rather than by the sieve tubes. To investigate the length of sieve tube continuity in Ricinus,a horizontal incision was made to the bark and the rate of exudationof phloem sap was monitored. Successive circumferential cutswere made above the exuding incision and progressively closerto it. In general, a girdling incision produced a transientdecrease in the rate of change of exudation rate (i.e. the firstderivative became more negative/less positive). The magnitudeof this response rose with exudation rate and fell with thedistance at which a girdling cut was made. Fitting an appropriatemodel yielded an estimate for contributory length of 69 ±6 cm. This was comparable with the distance of the initial tangentialincision from the stem apex, suggesting a continuous sieve tubesystem in Ricinus. A similar investigation on the petiole yieldedan estimate of around 7.0 cm. This lower estimate for contributorylength is believed to reflect a rapid sealing process that limitsthe distance of propagation of turgor-release rather than alimited length of sieve tube continuity. The results of this investigation do not support the relay hypothesisof phloem transport. Rather they suggest a continuous sievetube system which has a distributed capacity to load and unloadsolutes, and which may exhibit a sealing response when injured. Key words: Ricinus communis L, phloem transport, phleom unloading 相似文献
14.
Plant species were selected on the basis of abundant or no symplasmic continuity between sieveelement-companion-cell (SE-CC) complexes and adjacent cells in the minor veins. Symplasmic continuity and discontinuity are denoted, respectively, as symplasmic and apoplasmic minor-vein configurations. Discs of predarkened leaves from which the lower epidermis had been removed, were exposed to 14CO2. After 2 h of subsequent incubation, phloem loading in control discs and discs treated with p-chloromercuribenzenesulfonic acid (PCMBS) was recorded by autoradiography. Phloem loading was strongly suppressed by PCMBS in minor veins with symplasmically isolated SE-CC complexes (Centaurea, Impatiens, Ligularia, Pelargonium, Pisum, Symphytum). No significant inhibition of phloem loading by PCMBS was observed in minor veins containing sieve elements with abundant symplasmic connections (Epilobium, Fuchsia, Hydrangea, Oenothera, Origanum, Stachys). Phloem loading in minor veins with both types of SE-CC complex (Acanthus) had apoplasmic features. The results provide strong evidence for coincidence between the mode of phloem loading and the minor-vein configuration. The widespread occurrence of a symplasmic mode of phloem loading is postulated.Abbreviations PCMBS
p-chloromercuribenzenesulfonic acid
- SE-CC complex
sieve-element-companion-cell complex 相似文献
15.
Apoplastic Solute Concentrations of Organic Acids and Mineral Nutrients in the Leaves of Several Fagaceae 总被引:1,自引:0,他引:1
Ion chromatographic methods determined organic acids and mainnutrient minerals in the apoplastic solution from leaves ofseveral Fagaceae (Quercus ilex L., Quercus cerris L., Quercusvirgiliana (Ten.) Ten, and Fagus sylvatica L.). The anions oforganic acids found in high amounts (250 to 650 µM) werequinate, malate, and oxalate. Lactate, pyruvate, formate andacetate were detected in relatively low amounts with concentrationsbetween 20 and 200 µM. The total concentration of organicacids in the apoplastic sap ranged between 1.5 and 2 mM. Thetotal concentration of inorganic cations (K+, Mg2+, NH4+, Ca2+,Na+) and anions (C1, NO3, SO24 and PO34)in the apoplastic sap varied between 5 and 10 mM, and 0.35 and1.8 mM, respectively. We conclude that the concentration oforganic acid ions in the leaf apoplast depends mainly on theexchange with the leaf cells and is influenced by the electrochemicalgradient between the symplast and the apoplast in relation tothe water potential of the leaf. The determination of formateand acetate in the apoplastic compartment of leaves lend weightto the argument that the production of these acids by treesis a important emission source to the atmosphere. (Received June 9, 1998; Accepted April 8, 1999) 相似文献
16.
There is growing evidence that the phloem transport pathwayis leaky with passive unloading into the apoplast and activereloading from the apoplast. In this paper we report in vivomeasurements of unloading and reloading in immature stems ofbean expressed as a percentage per unit length of the photo-assimilateflow within the transport pathway. Gross unloading was up to6% cm-1 and net unloading up to 4% cm-1. Time constants of bulkflow through 10 cm of stem were about 4-6 min whereas thoseof net unloading were 8-13 min and of gross unloading, at themost, 7-8 min. Key words: Phloem transport, apoplast, bean stem 相似文献
17.
Phloem loading is the process by which photoassimilates synthesized in the mesophyll cells of leaves enter the sieve elements
and companion cells of minor veins in preparation for long distance transport to sink organs. Three loading strategies have
been described: active loading from the apoplast, passive loading via the symplast, and passive symplastic transfer followed
by polymer trapping of raffinose and stachyose. We studied phloem loading in Amborella trichopoda, a premontane shrub that may be sister to all other flowering plants. The minor veins of A. trichopoda contain intermediary cells, indicative of the polymer trap mechanism, forming an arc on the abaxial side and subtending a
cluster of ordinary companion cells in the interior of the veins. Intermediary cells are linked to bundle sheath cells by
highly abundant plasmodesmata whereas ordinary companion cells have few plasmodesmata, characteristic of phloem that loads
from the apoplast. Intermediary cells, ordinary companion cells, and sieve elements form symplastically connected complexes.
Leaves provided with 14CO2 translocate radiolabeled sucrose, raffinose, and stachyose. Therefore, structural and physiological evidence suggests that
both apoplastic and polymer trapping mechanisms of phloem loading operate in A. trichopoda. The evolution of phloem loading strategies is complex and may be difficult to resolve. 相似文献
18.
Gould, R. P., Minchin, P. E. H. and Young, P. C. 1988. The effectsof sulphur dioxide on phloem transport in two cereals.J.exp. BoL 39: 9971007. In vivo investigations using 11C-labelled photosynthate revealedthat there is a change in the patterns of tracer profiles whencereal leaves are exposed to SO2. The change after exposureto SO2 was interpreted in terms of a decrease in lateral waterflow into the sieve tubes brought about by reduced phloem loadingalong the length of a leaf. Analysis also revealed that thespeed of translocation was reduced, as expected by the Munchmodel of phloem transport. Key words: Sulphur dioxide, phloem transport, cereal leaves 相似文献
19.
Giaquinta R 《Plant physiology》1977,59(4):750-755
Autoradiographic, plasmolysis, and 14C-metabolite distribution studies indicate that the majority of exogenously supplied 14C-sucrose enters the phloem directly from the apoplast in source leaf discs of Beta vulgaris. Phloem loading of sucrose is pH-dependent, being markedly inhibited at an apoplast pH of 8 compared to pH 5. Kinetic analyses indicate that the apparent Km of the loading process increases at the alkaline pH while the maximum velocity, Vmax, is pH-independent. The pH dependence of sucrose loading into source leaf discs translates to phloem loading in and translocation of sucrose from intact source leaves. Studies using asymmetrically labeled sucrose 14C-fructosyl-sucrose, show that sucrose is accumulated intact from the apoplast and not hydrolyzed to its hexose moieties by invertase prior to uptake. The results are discussed in terms of sucrose loading being coupled to the co-transport of protons (and membrane potential) in a manner consistent with the chemiosmotic hypothesis of nonelectrolyte transport. 相似文献
20.
Concentrations and Transport of Solutes in Xylem and Phloem along the Leaf Axis of NaCl-treated Hordeum vulgare 总被引:5,自引:0,他引:5
WOLF OLAF; MUNNS RANA; TONNET M. LORRAINE; JESCHKE W. DIETER 《Journal of experimental botany》1990,41(9):1133-1141
Hordeum vulgare cv. California Mariout was established in sandculture at two different NaCl concentrations (0.5 mol m3control and 100 mol m3) in the presenceof 6.5 mol m3 K +. Between 16 and 31 d after germination,before stem elongation started, xylem sap was collected by useof a pressure chamber. Collections were made at three differentsites on leaves 1 and 3: at the base of the sheath, at the baseof the blade, i.e. above the ligule, and at the tip of the blade.Phloem sap was collected from leaf 3 at similar sites throughaphid stylets. The concentrations of K +, Na+, Mg2+ and Ca2+were measured. Ion concentrations in xylem sap collected at the base of leaves1 and 3 were identical, indicating there was no preferentialdelivery of specific ions to older leaves. All ion concentrationsin the xylem decreased from the base of the leaf towards thetip; these gradients were remarkably steep for young leaves,indicating high rates of ion uptake from the xylem. The gradientsdecreased with leaf age, but did not disappear completely. In phloem sap, concentrations of K+ and total osmolality declinedslightly from the tip to the base of leaves of both controland salt-treated plants. By contrast, Na+ concentrations inphloem sap collected from salt-treated plants decreased drasticallyfrom 21 mol m3 at the tip to 7.5 mol m3 at thebase. Data of K/Na ratios in xylem and phloem sap were used to constructan empirical model of Na+ and K+ flows within xylem and phloemduring the life cycle of a leaf, indicating recirculation ofNa+ within the leaf. Key words: Hordeum vulgare, xylem transport, phloem transport, NaCl-stress 相似文献