Concentration and Delivery of Abscisic Acid in Xylem Sap are Greater at the Shoot Base than at a Target Leaf Nearer to the Shoot Apex

Abstract: Samples of xylem sap from 5-week-old Ricinus corn-munis L. were obtained after severing a lamina, or shoot, from plants pressurized at the roots with air to raise hydrostatic xylem water potentials to atmospheric. In situ sap flow gauges, and mass flow measurements, showed that removing the lamina approximately doubted sap flow rate through the petiole stub that remained attached to the plant. This was a consequence of flow out of the roots being diverted along this low-resistance pathway and away from leaves higher in the canopy. Leaf and whole shoot excision temporarily released extra solutes in to sap as it discharged from the cut petiole or from the hypo-cotyl stump. This contamination prevented the use of sap extracted from detached lamina by overpressurizing in a Scholan-der bomb. To minimise distortions to sap flow and wound-induced contamination, estimates of in planta concentration and delivery (concentration × sap flow rate) of ABA and osmolality in xylem sap were made using sap flow rates measured before excision and concentrations in flowing sap collected approximately 30 mm after excision. At this time, effects of excision on solute contamination had subsided. The approach revealed that withholding water from upper roots increased ABA delivery from roots into the shoot base 3-fold. However, approximately half this ABA was lost en route to the youngest fully open leaf. This loss of ABA may explain the slow stomatal response to drying of upper roots shown by R. communis .     

The Flux and Distribution of Xylem Sap Calcium to Adaxial and Abaxial Epidermal Tissue 8

Inherent differences in the responses of stomata on abaxialand adaxial epidermal surfaces of leaves of Commelina communishave previously been suggested to be due to differences in theconcentrations of apoplastic Ca. Adaxial stomata have also beenreported to be more sensitive than abaxial stomata to appliedabscisic acid (ABA). The aims of these experiments were to determinethe validity of these conclusions and to see if xylem sap Cahas a role in determining the response of stomata to ABA. It can be shown from measurements of relative stomatal resistance(determined with a viscous flow porometer) and stomatal conductancethat stomata were more open in plants grown on 8-0 mol m^–3Ca, than with those grown on 2-0 mol m^–3 Ca. When attachedleaves were fed with ABA via the transpiration stream neitherthe extent nor the rate with which conductance declined wasdependent on Ca nutrition. The extent of Ca accumulation within both epidermes was relatedto the concentration of Ca in the rhizosphere and in the xylemsap. It did not, however, appear to reflect the apparent differencesin the flux of the transpiration stream between the two epidermes.Plants growing at the lower Ca concentration accumulated proportionallymore epidermal Ca relative to Ca in xylem sap. The evidencepresented suggests that Ca movement from the xylem to the epidermiscannot be simply described by a mass flow model, and that thedistribution of Ca is not an adequate explanation of the differencesin the behaviour of adaxial and abaxial stomata. The potentialrole for changes in xylem sap Ca to act as a regulator of stomatalbehaviour are discussed. Key words: Abscisic acid, calcium, Commelina communis L., stomatal conductance     

Chitinase in Cucumber Xylem Sap

A chitinase activity was detected in fractions of xylem sap collected from the cut surface of cucumber stems. A 28-kDa acidic protein was purified from the active fractions and its N-terminal amino acids sequence was found to be identical to that of a chitinase gene. Cucumber roots produce and secrete an acidic chitinase, one of the PR proteins, into xylem sap and deliver it to aboveground organs.     

Some Constituents of Xylem Sap and their Possible Relationship to Xylem Differentiation

Bleeding sap of Actinidia chinensis and Betula populifolia andguttation fluidof Avena sativa were analysed for sugars, amino-acids,auxin, and certain enzymes. A wide range of amino-acids wasfound in all three. Auxin was not detected in the bleeding sap,but was present in Avena guttation fluid (5.1 µg IAA equivalent/l).‘IAA oxidase’, acid phosphatase, ribonuclease, deoxyribonuclease,and protease were detected in the bleeding sap and guttationfluid. The possibility that some of the substances found insap and guttation fluid are products of autolysing, differentiatingxylem cells in the roots is discussed.     

土壤干旱条件下木质部汁液成分变化及其在根冠信号传递中的作用

介绍了植物木质部汁液收集方法和干旱条件下 ,蒸腾流中碳水化合物、蛋白质、pH等的变化 ,并对这些成分变化在根冠信号传递中的可能作用进行了讨论     

Xylem Sap from Actinidia chinensis: Gradients in Sap Composition

In early spring, just prior to leaf break, there were substantialgradients in the concentration of many solutes in xylem sapcollected by vacuum extraction from shoots of different ages,from the branches, trunk and roots of mature Chinese gooseberryvines (Actinidia chinensis Planchon) For most nutrients therewas a progressive fall in concentration from youngest shootsdown to the roots and nitrate was the only nutrient to showa trend in the opposite direction These gradients in concentrationare probably sufficient to account for most of the changes observedin the composition of bleeding xylem sap during the first fewhours of bleeding after a branch is cut or wounded Actinidia chinensis, Chinese gooseberry, kiwifruit, xylem sap, nutrient gradients     

Antitranspirant Activity in Xylem Sap of Maize Plants

Xylem sap from unwatered maize plants was collected and testedfor antitranspirant activity. Two assays were used. These werea transpiration assay with detached wheat leaves and a stomatalbio-assay involving the direct microscopic observation of epidermisof Commelina communis. The reduction in transpiration of detached wheat leaves promotedby xylem sap could be duplicated almost exactly by the applicationof solutions of ABA of equivalent concentration to that foundin the xylem sap. Removal of virtually all the ABA from thexylem sap, using an immunoaffinity column, removed virtuallyall the antitranspirant activity in both assays. These results are discussed in the context of other resultswhich suggest the presence of as-yet unidentified inhibitorsin the xylem sap of unwatered plants. We suggest that with maize plants at least, stomatal responsesto soil drying can be entirely explained by enhanced concentrationof ABA in the xylem stream. Key words: Antitranspirant activity, ABA, ABA bio-assay, xylem sap     

Proteins and Carbohydrates in Xylem Sap from Squash Root

The xylem sap from squash roots was collected from the cut surfaceof stems, and the proteins and carbohydrates in the sap wereanalyzed. The sap contained 18.6 µg ml^–1 proteinand the major polypeptides were as follows: 1) two polypeptides,of 75 and 40 kDa, with high-mannose glycans, the levels of whichincreased for about 24 h after cutting and then decreased; 2)a 32-kDa polypeptide, which appeared soon after cutting, disappearedand then reappeared again 48–64 h after cutting; and 3)a 19-kDa and a 14-kDa polypeptide, which were present constitutively.The carbohydrates contained in the xylem sap were fractionatedinto 80% ethanol-soluble and -insoluble material, and whichwere analyzed by high-performance liquid chromatography, gaschromatography and enzymatic mathods. The former fraction containedconsiderable amounts of myo-inositol and fructose as free sugarsand oligosaccharides composed mainly of galactose, arabinoseand glucose. The latter contained polysaccharides composed mainlyof uronic acids, galactose and arabinose. The possible significanceof these substances, which may mediate the interactions betweenthe root and the aerial organs, is discussed. (Received April 20, 1992; Accepted July 4, 1992)     

Electrochemical Relations in the Transfer of Ions to the Xylem Sap of Maize Roots

The difference in electrical potential between the xylem exudateof isolated roots of 1-week-old maize seedlings and the culturesolution surrounding the roots has been determined togetherwith the concentrations of potassium, calcium, chloride, andsulphate in the xylem sap. The difference in electro-chemicalpotential (µ) for these ions has been calculated fromthe measurements. The effects on µ of varying the saltstatus of the roots, the composition of the culture solutionand of 2-4-dinitrophenol have been examined. µ for potassiumand chloride was always positive, implying that movement ofthese ions to the xylem sap was under metabolic constraint.However, pretreatment of the maize seedlings with potassiumchloride and increasing levels of dinitrophenol in the culturesolution over the exudation period caused little or no significantchange in µ for potassium although the rate of movementof ions to the xylem was substantially reduced. For calcium,µ was negative with roots in dilute culture solutionsin the absence of dinitrophenol, implying that calcium couldenter the xylem by passive diffusion. Addition of dinitrophenolchanged the sign of µ and thus brought about an apparentlyactive transport of calcium.Only in the absence of competinganions was the rate of entry of chloride significantly correlatedwith µ, and no such relationship was found for potassiumor calcium individually. These results encourage doubt as towhether measurements of µ provide a valid basis for decidingto what extent the movement of individual ions depends on specific‘active’ or ‘passive’ transport processes.Thedifference in electrical potential appears to be a characteristicof the living root and to depend on the total concentrationof ions in the external solution and on their rate of transferinto the xylem sap.     

Levels of Sorbitol in Bleeding Sap and in Xylem Sap in Relation to Leaf Mass and Assimilate Demand in Apple Trees

Removal of fruits and treatment with SADH (succinic acid 2,2-dimethylhydrazide) were used to change the balance between sources and sinks for photosynthates in Malus domestica‘Golden Delicious’. Sorbitol and sugar content were measured in bleeding sap, in xylem sap prepared by suction, and in 80% methanol extracts of the roots. Concentration as well as total amount of sorbitol in bleeding sap sampled in July and September were lower in fruiting than in defruited trees, and so was the total amount of sorbitol in xylem sap from the trunk. SADH treatment tended to reduce the sorbitol content. Sorbitol in root extracts, expressed as percentage of methanol (80%) insoluble root dry matter, was highest in fruiting trees; but root dry matter was here less than half of that in defruited trees. Sorbitol content in xylem sap as well as sorbitol + sugar percentage of roots showed a distinct maximum in late winter followed by a heavy decrease during spring. It is suggested that sorbitol in xylem sap during the growth season represents a return transport from the roots, and that the level of sorbitol in this return transport reflects, to a certain degree, the ratio between leaf area and assimilate demand by the tree.     

Hormone Signals from Roots to Shoots of Sunflower (Helianthus annuus L.). Moderate Soil Drying Increases Delivery of Abscisic Acid and Depresses Delivery of Cytokinins in Xylem Sap

We quantified abscisic acid and a cytokinin trans zeatin ribosideas potential positive or negative signals in root to shoot communicationin sunflower plants (Helianthus annuus L.) growing in dryingsoil. Delivery rates rather than concentration values were usedbecause the former are less subject to change as a result ofdifferences in sap flow through dilution. ABA concentrationand delivery rate increased under the mild drought stress. Incontrast, t-ZR concentration did not change under mild stressalthough delivery rates decreased significantly. With more severedrought stress, both delivery rates and concentration of t-ZRdecreased considerably while ABA concentration and deliverywere enhanced markedly. Root ABA contents mirrored those ofxylem ABA. Helianthus annuus ; soil drying; root signals; ABA; cytokinins; delivery rate; delivery rate     

Relationship of Xylem Embolism to Xylem Pressure Potential, Stomatal Closure, and Shoot Morphology in the Palm Rhapis excelsa

Xylem failure via gas embolism (cavitation) induced by water stress was investigated in the palm Rhapis excelsa (Thumb.) Henry. Xylem embolism in excised stems and petioles was detected using measurements of xylem flow resistance: a decrease in resistance after the removal of flow-impeding embolisms by a pressure treatment indicated their previous presence in the axis. Results supported the validity of the method because increased resistance in an axis corresponded with: (a) induction of embolism by dehydration, (b) increased numbers of cavitations as detected by acoustic means, (c) presence of bubbles in xylem vessels. The method was used to determine how Rhapis accommodates embolism; results suggested four ways. (a) Embolism was relatively rare because pressure potentials reach the embolism-inducing value of about −2.90 megapascals only during prolonged drought. (b) When embolism did occur in nature, it was confined to the relatively expendable leaf xylem; the stem xylem, which is critical for shoot survival, remained fully functional. (c) Even during prolonged drought, the extent of embolism is limited by complete stomatal closure, which occurred at the xylem pressure potential of −3.20 ± 0.18 megapascals. (d) Embolism is potentially reversible during prolonged rains, since embolisms dissolved within 5 h at a pressure potential of 0.00 megapascals (atmospheric), and xylem sap can approach this pressure during rain.     

Xylem Sap from Actinidia chinensis: Apparent Differences in Sap Composition Arising from the Method of Collection

Large differences in composition were found between xylem sapcollected from Actinidia chinensis (Chinese gooseberry or kiwifruit) as bleeding sap and sap collected by vacuum extraction.A comparison of saps collected by the two methods has littlemeaning, however, unless the position on the plant from whichsap was collected and the prior treatment of the plant are specified.Furthermore the composition of bleeding sap changes rapidlywith time, probably because of marked gradients in concentrationof individual solutes in the xylem sap from the base to thetop of the plant. Contamination of vacuum-extracted sap by cellularcontents was shown to be insignificant. Sap collected as bleeding sap and by vacuum extraction are ofsomewhat different origins. It would be difficult to predictthe composition of bleeding sap simply from a knowledge of vacuum-extractedsap: it may be similarly unwise to predict the composition ofthe transpiration stream from that of vacuum extracted sap. Actinidia chinensis, kiwi fruit, Chinese gooseberry, xylem sap, bleeding sap, vacuum-extraction     

Collection of Xylem Sap at Flow Rate Similar to in vivo Transpiration Flux

We have explored a method to collect xylem sap using a Scholanderpressure chamber for potted plants. Intact root system in potswhich fitted the pressure chamber was pressurised at a pneumaticpressure numerically equal to the absolute value of shoot waterpotential. The rate of xylem flow obtained from the stem stumpunder such pressure was found similar to the rate of transpirationbefore detopping. The rate of pressurised flow from detop-pedroots was linearly related to the pressure applied in both well-wateredand soil-dried plants. The osmotic concentration of the xylemsap was negatively related to the rate of volume flow, suggestingthe necessity to collect xylem sap at in vivo flow rate if originalsolute concentration is to be evaluated. The concentration ofABA in the xylem sap, however, did not show such a relationshipwith water flux. Both well-watered and soil-dried plants showedthe concentration of ABA in xylem sap largely stable with arange of volume flow rate, indicating a linear relationshipbetween the rate of ABA delivery through xylem and that of volumeflow. We also compared the concentrations of ABA in xylem sapsequentially collected from pressurised roots with that fromdetached shoots of the same plants. The concentration of ABAin the initial saps from shoots showed to be similar to thatfrom roots. However, a decrease in the concentration of ABAin the xylem sap collected from detached leaf or twig was observedwhen more volume of sap was collected, which might also be dependenton the plant species and the volume of xylem vessels concerned. (Received February 3, 1997; Accepted October 7, 1997)     

Chemical Composition of Bleeding Xylem Sap from Kiwifruit Vines

A study of the chemical composition and charge balance was madeof bleeding xylem sap collected from excised one-year-old extensionshoots of healthy, Mn-deficient, Mn-toxic and Zn-deficient kiwifruitvines (Actinidia deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson)immediately prior to leafburst. The exudates were analysed formacronutrient cations and anions, trace elements, amino acids,organic acids and sugars. Major charged species measured wereCa (13.3 mM), K (8.9 mM), Mg (5.6 mM), malate (12.5 mM) andphosphate (5.8 mM). Glutamine (12 mM) was the predominant Ncarrier identified, accounting for 58 per cent of the totalN followed by NO₂^–-N (4.5 per cent), NH₄⁺-N (3.5 per cent)and arginine-N (2.9 per cent). Approximately 22 per cent ofthe N was in a hydrolysable proteinaceous fraction comprisingmainly glutamine and glutamate. Eighteen free proteinaceousamino acids were idetified in sap, the most abundant being glutamine,glutamic acid, valine, isoleucine and phenylalanine. Computersimulation of the chemical composition predicted that in additionto hydrated cations, ion pairs formed between inorganic components(SO₄^2–, HPO₄^2–, H₂PO₄^–) and cations (Ca²⁺,Mg²⁺, Mn²⁺), plus metal-organic ligand complexes (Ca Malate,Zn Malate, FeCit, CuHis, CuGln) are important species involvedin translocation. The solubility product of hydroxyapatite wasexceeded in all exudates although in vitro precipitation wasnot observed. To achieve electroneutrality with the componentsmeasured, however, formation of precipitate precursors (hydroxyapatitenuclei) had to be assumed. Irregularities in Mn nutrition (butnot Zn) were clearly indicated by the elemental compositionof exudate suggesting the use of sap analysis as a possiblepre-season indicator of nutritional status for this species. Actinidia deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson, kiwifruit, xylem sap composition, trace metals, amino acids, organic acids     

Xylem Sap Composition in Apple Trees: Effect of the graft union

This paper records studies on the xylem sap from above and belowthe graft unions of apple trees with M·9, M·7and MM.104 rootstocks. The dry weight of solutes in sap fromabove the unions of the M·9 trees was between 30 and50 per cent lower than in sap from below, while the volume ofsap exuded was not reduced. The graft unions of the M·7and MM·104 trees had no significant effect on the xylemsap. These results are discussed in relation to the dwarfing effectsof rootstocks and interstocks.     

Na+, K+ and Cl- in Xylem Sap Flowing to Shoots of NaCl-Treated Barley

Munns, R. 1985. Na⁺, K⁺ and Cl^– in xylem sap flowing toshoots of NaCl-treated barley.—J. exp. Bot. 36: 1032–1042. Na⁺, Cl^– and K⁺ concentrations were measured in xylemsap obtained by applying pressure to the roots of decapitatedbarley plants grown at external [NaCl] of 0, 25, 50, 100, 150and 200 mol m^–3. For any given NaCl treatment, ion concentrationsin the xylem sap were hyperbolically related to the flux ofwater. Ion concentrations in sap collected at very low volumefluxes (without applied pressure) were 5–10 times higherthan in sap collected at moderate fluxes (under pressure). Fora given moderate volume flux, Na+ concentration in the xylemsap, [Na⁺]_x, was only 4.0 mol m^–3 at external [NaCl] of25–150 mol m^–3, and increased to 7.0 mol m^–3at 200 mol m^–3. [Cl-]x showed a similar pattern. Thisshows there would be little difference in the rate of uptaketo the shoot of plants at 25–150 mol m^–3 externalNaCl and indicates little change even at 200 mol m^-3 NaCl becausetranspiration rates would be much lower. Thus the reduced growthof the shoot of plants at high NaCl concentrations is not dueto higher uptake rates of Na⁺ or Cl^–. The fluxes of Na⁺, Cl^– and K^– increased non-linearlywith increasing volume flux indicating little movement of saltin the apoplast. The flux of K⁺ increased even when [K⁺]_x wasgreater than external [K⁺], indicating that membrane transportprocesses modify the K⁺ concentration in the transpiration streamas it flows through the root system. Key words: -Xylem sap, Na⁺, K⁺, Cl^– fluxes, salinity, barley     

Xylem Sap from Actinidia chinensis: seasonal Changes in Composition

Seasonal variation was followed in the content of total a-aminoacids, arginine, calcium, total carbohydrate, ß-galactosidaseactivity, magnesium, nitrate, phosphatase activity, phosphateand sulphate in vacuum-extracted xylem sap from Actinidia chinensisvar. hispida, the Chinese gooseberry or kiwifruit. There wasa marked increase in the concentration of most sap componentsjust prior to leaf emergence followed by a rapid decrease afterthe leaves had expanded. Experiments with excised extensionshoots showed that much of this spring-time increase in concentrationsof sap components was due to mobilization of nutrients withinthe shoot itself. Sap from the trunk and the older brancheschanged less in composition than did sap from the younger partsof the plant. The amplitude and direction of trends in concentrationof sap from the different parts of the plant varied with nutrientand with time. Analysis of vacuum-extracted xylem sap collectedduring periods of rapid transpiration from early summer onwardsgives a reliable indication of the composition of the transpirationstream. Actinidia chinensis, Chinese gooseberry, kiwifruit, storage reserves, xylem sap, amino acids, arginine, calcium, carbohydrate, ßgalactosidase, magnesium, nitrate, phosphatase, phosphate, potassium, sulphate     

转Bt 基因抗虫棉(Gossyposium)伤流中Bt 毒蛋白的运输

本文以常规棉品种‘石远321’和抗虫棉品种‘SGK321’与‘99B’为材料, 通过考马斯亮蓝和ELISA方法分析了伤流中可溶性蛋白和Bt(苏云金芽孢杆菌)毒蛋白含量。结果发现, 转基因抗虫棉伤流中可溶性蛋白含量显著高于常规棉, 并在抗虫棉伤流中检测到了Bt毒蛋白, 而常规棉伤流中没有Bt毒蛋白的存在。通过嫁接实验研究发现, 将常规棉嫁接到转Bt基因抗虫棉砧木上, 叶片中也有Bt毒蛋白的积累。这些结果说明, Bt毒蛋白可以通过木质部伤流液向地上部运输, 并在叶片中积累, Bt毒蛋白由根系向地上部的运输对棉花的抗虫性是有益的。