Xylem sap proteins

Xylem sap from apple (Malus domestica Borkh), peach (Prunus persica Batsch), and pear (Pyrus communis L.) twigs was collected by means of pressure extrusion. This sap contained a number of acidic peroxidases and other proteins. Two other sources of xylem sap used in this study were stem exudates and guttation fluid. Similar peroxidases were also found in stem exudates and guttation fluids of strawberry (Fragaria x ananassa Duch.), tomato (Lycopersicum esculentum L.), and cucumber (Cucumis sativus L.). Isoelectric focusing activity gels showed that two peroxidases (isoelectric point [pl] 9 and pl 4.6) were present in initial stem exudates collected in the first 30 minutes after excision. Subsequent samples of stem exudate collected contained only the pl 4.6 isozyme. The pl 4.6 peroxidase isozyme was also found in root tissue and guttation fluid. These observations suggest that roots produce and secrete the pl 4.6 peroxidase into xylem sap. Cucumber seedlings were treated with 100 microliters per liter ethylene for 16 hours and the exudate from decapitated hypocotyl stumps was collected over a 3 hour period. Ethylene increased the peroxidase activity of stem exudates and inhibited the amount of exudate released. These observations suggest that xylem sap peroxidase may play a role in plugging damaged vascular tissue.     

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     

The Composition of Phloem Exudate and Xylem Sap from Tree Tobacco (Nicotiana glauca Grah.)

The composition of xylem sap and exudate from stem incisionsof Nicotiana glauca Grah. was compared in detail. Exudationfrom stem incisions occurred over a 5 min period in certainplants, enabling collection of 5–30 µl of sap. Therate of exudation showed an exponential decline. Exudate hada high dry matter content (170–196 mg ml^–1) andhigh sugar (sucrose) levels. Xylem sap had a low pH (5.8) andexudate a pH of 7.9. Glutamine dominated the amino compoundsin xylem sap and exudate, and K⁺ was the major cation. Totalamino compounds in stem exudate reached 10.8 mg ml^–1 whereasxylem sap contained much lower levels (0.28 mg ml^–1).All mineral elements and amino compounds with the exceptionof calcium were more concentrated in stem exudate than in xylemsap. Sucrose was labelled heavily in stem exudate following pulsingof an adjacent leaf with ¹⁴CO₂. A concentration gradient ofsugar (2.1 bar m^–1) was recorded for stems. Levels ofsucrose, amino compounds and K⁺ ions in stem exudate showeda diurnal periodicity. Each commodity reached maximum concentrationat or near noon and minimum concentration about dawn. The evidencesuggests that exudate from stem incisions of N. glauca is arepresentative sample of solutes translocated in the phloem. Nicotiana glauca Grah., phloem sap, xylem sap, sucrose, amino compounds, mineral ions     

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     

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     

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     

Xylem conduction and cavitation in Hevea brasiliensis

Clones of Hevea were studied in an attempt to discover the reasonsfor differences in the hydraulic performance of xylem. Differencesbetween clones were determined, including hydraulic conductivityand conduit width and length distributions. However, it hasproved difficult to reconcile anatomical differences with physiologicalperformance for use in future plant breeding programmes. When leaf relative water content (RWC) had been reduced fromabout 95% to 85%, the hydraulic conductivity of petioles decreasedsharply to about 40% of the initial value. This value correspondedwith xylem sap tensions of 1.8–2.0 MPa. Acoustic detectionexperiments revealed that this reduction in hydraulic conductivitycoincided with the greatest occurrence of cavitation. It seemsinescapable that the reduction in hydraulic conductivity wascaused by embolization; thereafter gas bubbles blocked the flowof water inside many of the conduits. There was some indicationthat eventually such bubbles might be dissolved, because thehydraulic conductivity increased again if specimens were fullyrehydrated. Apparently, the incidence of cavitation coincides with the entryof gas bubbles via ultramicroscopic pores into the conduitsthrough the walls according to the air-seeding hypothesis. Whena petiolate leaf is tested in a pressure chamber it is impossibleto make satisfactory measurements of a balancing pressure beyondc. 1.8–2.0 MPa, because air bubbles, mixed with sap andescaping from the conduits, form a persistent froth. Xylem transportin Hevea seems to be disrupted relatively easily under waterstress which is a feature of other tropical species adaptedto rainforest–type environments Key words: Hevea, xylem, cavitation, conduit, hydraulic conductivity     

Concentrations and Transport of Solutes in Xylem and Phloem along the Leaf Axis of NaCl-treated Hordeum vulgare

Hordeum vulgare cv. California Mariout was established in sandculture at two different NaCl concentrations (0.5 mol m^–3‘control’ and 100 mol m^–3) in the presenceof 6.5 mol m^–3 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 m^–3 at the tip to 7.5 mol m^–3 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     

Release of Guttation Fluid from Passive Hydathodes of Intact Barley Plants. II. The Effects of Abscisic Acid and Cytokinins

Guttation was used as a non-destructive way to study the flowof water and mineral ions from the roots and compared with parallelmeasurements of root exudation. Guttation of the leaves of barley seedlings depends on age andon the culture solution. Best rates of guttation were obtainedwith the primary leaves of 6- to 7-day-old seedlings grown onfull mineral nutrient solution. The growing leaf tissue becomessaturated with K⁺ below 1.5 mM K⁺ in the medium, whereas K⁺concentration in the guttated fluid still increases furtheras K⁺ concentration in the medium is raised. At 3 mM K⁺ averagevalues of guttation were 1.4–2.4 mm³ h^–1 per plantwith a K⁺ concentration of 10–20 mM; for exuding plantsthe flow was 4.2–7.6 mm³ h^–1 per plant and K⁺ concentration35–55 mM. Abscisic acid (ABA) at 10^–6 to 10^–4 M 0–2h after addition to the root medium increased volume flow ofguttation and exudation and the amount of K⁺ exported. Threeh after addition of ABA both volume and amount of K⁺ were reduced.There was an ABA-dependent increase in water permeability (Lp)of exuding roots shortly after ABA addition. Later Lp was decreasedby 35 per cent and salt export by 60 per cent suggesting aneffect of ABA on salt transport to the xylem apart from itseffect on Lp. Benzyladenine (5 x 10^–8 to 10^–5 M)and kinetin (5 x 10^–6 M) progressively reduced volumeflow and K⁺ export in guttation and exudation and reduced Lp. Guttation showed a qualitatively similar response to phytohormonesas found here and elsewhere using exuding roots. Hordeum vulgare L., barley, guttation, abscisic acid, cytokinins, benzyl adenine, kinetin     

Changes in the Nitrogen Compounds of Xylem Sap of Mulberry (Morus alba L.) during Regrowth after Pruning

Changes in fresh and dry weights and total nitrogen in stemsections of mulberry (Morus alba L.) and seasonal fluctuationin the amounts of exudate, pH and nitrogen compounds in xylemsap from cut stems of the plant after pruning have been studied.The amount and concentrations of nitrogen compounds in the sapchanged during the experimental period, but nitrate-nitrogenand ammonia-nitrogen were constant constituents, and asparaginewas quantitatively the major organic nitrogen compound. Smalleramounts of glutamine, aspartic acid and glutamic acid were alsofound, but no ureides or alkaloids were detected. Relationshipsbetween growth and nitrogen in xylem sap of mulberry and therole and importance of asparagine in nitrogen metabolism arediscussed. Morus alba L., mulberry, asparagine, exudates, nitrogen, amino-acids, xylem sap, stem growth, aspartic acid, glutamic acid, ureides     

Dependence of Calcium Transport into Strawberry Leaves on Positive Pressure in the Xylem

Strawberry plants were cultured in concentrated and dilute nutrientsolutions by day and night, factorially. Guttation decreased,leaf tipburn increased and calcium in emerging leaves was reducedwhen solutions were more concentrated at night. Nutrient concentrationin the daytime was much less important for these responses.The effects were similar when the more concentrated solutioncontained additional Ca²⁺, NO₂^–, Cl^– and SO₄^2–or extra of all the major nutrients in the same proportions.When the solution was made stronger by adding extra Mg²⁺, NO₂^–,Cl^– and SO₄^2– the guttation, tipburn and calciumdifferences were basically similar to those in the previousexperiment but with an added effect explained by a competitivesuppression of calcium uptake caused by the extra magnesium.Thus, both nutrient strength and cation balance are importantfor preventing strawberry leaf tipburn. The results accord with the hypothesis that calcium translocationinto pre-emerged strawberry leaves depends on the attainmentof a positive water pressure in the xylem at night, when transpirationlosses are minimal. Fragaria ananassa Duchesne, Strawberry, calcium, tipburn, root pressure, nutrient concentrations     

Adaptive Growth Responses to Osmotic Stress of Hypocotyl Sections of Vigna unguiculata: Roles of the Xylem Proton Pump and IAA

The growth responses to osmotic stress of hypocotyl sectionsof Vigna unguiculata were studied by the xylem perfusion method.Hypocotyl sections shrank upon exposure to osmotic stress. Sectionsshowed no adaptive responses to osmotic stress when they werein an IAA-depleted condition as a result of perfusion with solutionsthat lacked IAA for 3–4 h. The correlation between thegrowth rate and the membrane potential of the xylem/symplastboundary (V^px) was very limited in the absence of IAA. By contrast,hypocotyl sections showed distinct adaptive responses to osmoticstress after perfusion with solutions that contained 10 µMIAA. In the presence of IAA, V^px increased in the negative directionand growth resumed in spite of the osmotic stress. The growthrate was closely correlated with the xylem membrane potential.Hyper-polarization of the membranes of the xylem/symplast boundaryalways preceded the recovery of growth under osmotic stress.It appears that IAA is essential for the adaptive recovery ofgrowth under osmotic stress and, moreover, that the xylem protonpump plays an indispensable role in modulating the growth ofhypocotyl sections. This result confirms prediction of an earliersimulation study using the apoplast canal model [Katou and Furumoto(1986) Protoplasma 133: 174, Katou and Enomoto (1991) PlantCell Physiol. 32: 343]. (Received June 27, 1996; Accepted October 28, 1996)     

Free Amino-acids in the Endosperm of the Developing Coconut (Cocos nucifera)

The free amino-acids in the sap flowing from the incised inflorescenceof the coconut palm (Cocos nucifera) and in the liquid and solidendosperm of the coconut at various stages of development (4–12months from the time of opening of the spathe) have been studiedby paper and ion-exchange chromatography. The chief amino-acids in the sap were in decreasing order ofmagnitude: glutamic acid, aspartic acid, glutamine, serine,and asparagine. Smaller amounts of threonine, alanine, -aminobutyricacid, proline, valine, arginine, and tryptophan were found,along with traces of tyrosine, ß-alanine, lysine,histidine, leucine, isoleucine, and methionine. The chief amino-acids in the liquid endosperm of the nut until6 months of age were alanine, glutamic acid, serine, valine,and proline with smaller amounts of asparagine, aspartic acid,glycine, threonine, leucine, isoleucine, and glutamine. Thealanine, glutamic acid, proline, and -aminobutyric acid contentsof the liquid endosperm increased greatly as the solid endospermwas laid down, ultimately forming about 75 per cent. of thetotal free amino-acids. Nineteen amino-acids were detected atthe 8–10-month stage. -Aminobutyric acid appears in the liquid endosperm soon afterthe solid endosperm commences to form, and increases strikinglythereafter. It was also found in the free amino-acids of thesolid endosperm at all stages of development. This amino-acidwas not found in the acid hydrolysate of coconut globulin. The free amino-acids in the solid endosperm were found to reflectqualitatively the free amino-acid composition of the correspondingliquid endosperm. In addition, ß-alanine, -aminobutyricacid, phenylalanine, and tryptophan were present in small amounts.Alanine, serine, glutamic acid, and -aminobutyric acid, increasedwith age of the nut while the others increased up to 6 monthsand then decreased, only traces being found at maturity exceptin the case of aspartic acid, proline, and threonine. Twenty-oneamino-acids were detected in the free amino-acids of the solidendosperm. The source of the free amino-acids in the liquid endosperm andthe possible use of these amino-acids for protein synthesisin the coconut are briefly discussed.     

Production of Indole-3-Acetic Acid by Bradyrhizobium japonicum: A Correlation with Genotype Grouping and Rhizobitoxine Production

Bioassays show that rhizobitoxine-producing strains of Bradyrhizobiumjaponicum excreted another phytotoxic compound into their culturefluid. This compound was purified and identified by HPLC andmass spectrometry as indole-3-acetic acid (IAA). The levelsof IAA produced by the different strains of B. japonicum, forwhich the genotype groups have been determined with respectto the degree of base substitution in and around nifDKE, werequantified using gas chromatography/mass spectrometry and adeuterated internal standard. Genotype II strains, which producerhizobitoxine, excreted more than 20µof IAA into theirculture fluid. However, no IAA was detected in the culture supernatantsof genotype I strains, which do not produce rhizobitoxine. Thiswas true even when tryptophan was added to the medium. Moreover,cells of genotypes I and II strains, which were grown underour culture conditions, did not show IAA degradation activity.These results suggest that, in wild-type B. japonicum strains,complete IAA biosynthesis is confined exclusively to genotypeII strains that produce rhizobitoxine. (Received April 9, 1990; Accepted October 6, 1990)     

Composition of Amino Compounds Transported in Xylem of Casuarina sp.

Seedlings (180-d-old) of Casuarina cunninghamianaM L., C. equisetifoliaMiq. and C. glauca Sieber inoculated with each of two differentsources of Frankia, were analysed for translocated nitrogenouscompounds in xylem sap. Analyses were also made on sap fromnodulated and non-nodulated plants of C. glauca grown with orwithout a range of levels of combined nitrogen. Xylem exudateswere collected from stems, roots, and individual nodules ofnodulated plants and from stems and roots of non-nodulated plants.While the proportional composition of solutes varied, the samerange of amino compounds was found in xylem sap from the threedifferent symbioses. In C. glauca asparagine was the major aminoacid in the root sap followed by proline, while in symbioticC. cunninghamiana arginine accounted for more than 25% of theamino compounds. Citrulline was the major translocated productfound in the stem exudate of symbiotic C. equisetifolia. Increasingconcentrations of ammonium nitrate in the nutrient solutionresulted in increasing levels of free ammonia and glutaminein xylem sap from stems of nodulated and non-nodulated C. glauca,but there was relatively little change in the prominent solutes,e.g. citrulline, proline, and arginine. The composition of nitrogenoussolutes in stem or root exudates of C. glauca was similar tothat of exudate collected from individual nodules and on thisbasis it was not possible to distinguish specific products ofcurrent N₂ fixation in xylem. The main differences in N solutecomposition between the symbioses were apparently due to hostplant effects rather than nodulation or the levels of combinedN. Also, the data indicate that the use of the proportion ofN in sap as citrulline (or indeed any other organic N solute)could not be used as an index of nitrogen fixation.     

The Effects of Temperature on Vegetative and Early Reproductive Growth of a Cold-Tolerant and a Cold-Sensitive Line of Phaseolus vulgaris L. 2. Nodular Uricase, Allantoinase, Xylem transport of N and Assimilation in Shoot Tissues

The activities of nodular uricase and allantoinase, the compositionof bleeding sap N, estimated rates of xylary N translocationand ureide assimilation in shoot tissues were compared in acold-tolerant (194) and sensitive (Seafarer, SF) line of nodulatedPhaseolus vulgaris grown under three different temperature regimes.Uricase activity increased with increasing growth temperatureand was generally greater in nodules of 194 than in SF at anyparticularly temperature. Extractable allantoinase activity,on the other hand, was highest in nodules from plants grownat the coolest temperature (15/10 C day/night) and there waslittle or no difference in activity between the lines. There was little difference in sap composition between linesor amongst temperature treatments. Ureides contributed between80–91 percent of the total sap N in both lines grown at25/15 or 20/15 C with a slightly lower per cent (65–84)when grown at 15/10 C. Estimated rates of N translocation werehigher in 194 than SF at the coolest growth temperature. Increasesin rates of N translocation between successive harvests of eitherline were often correlated with increases in total N accumulationand also an accumulation of ureides in stems plus petioles butnot leaves. Generally leaves assimilated all of the ureidesinto other compounds at all growth temperatures. Nodules andshoots of either line did not accumulate ureides at 15/10 C.194 Accumulated greater amounts of ureides in stems and petiolesthan SF when grown at the two warmer temperatures. The resultsare discussed in relation to the ability of 194 to fix greateramounts of N than SF at suboptimal growth temperatures. Phaseolus vulgaris, common bean, uricase, allantoinase, sap composition, ureide assimilation, low temperature stress     

Carbon Flow from Nodulated Roots to the Shoots of Soybean (Glycine max L. Merr.) Plants: An Estimation of the Contribution of Current Photosynthate to Ureides in the Xylem Stream

Kouchi, H. and Higuchi, T. 1988. Carbon flow from nodulatedroots to the shoots of soybean {Glycine max L. Merr.) plants:An estimation of the contribution of current photosynthate toureides in the xylem stream.–J. exp. Bot. 39: 1015–1023. Well-nodulated, water-cultured soybean plants were allowed toassimilate ¹³CO₂ at a constant specific activity for 10 h andthe ¹³C-labelling of total carbon and ureides in xylem sap wasinvestigated. Labelled carbon appeared very rapidly in the xylem stream. Percentageof labelled carbon (relative specific activity, RSA) in xylemsap was 18% at 2 h after the start of ¹³CO₂ assimilation andreached 53% at the end of the 10 h assimilation. The amountof labelled carbon exported from nodulated roots to the shootsvia the xylem during the 10 h labelling period accounted for33% of total labelled carbon imported into the nodulated roots.Ureides (allantoin and allantoic acid) in xylem sap were stronglydependent on currently assimilated carbon. The RSA of ureidesin xylem sap had reached 83% at the end of the assimilationperiod. Labelled carbon in ureides accounted for 51% of totallabelled carbon returned from nodulated roots to the shootsvia the xylem during the 10 h assimilation period. A treatmentwith 20 mol m^–3 nitrate in the culture medium for 2 ddecreased the ureide concentration in the xylem sap slightly,but greatly decreased the RSA of ureides. By comparing the data with the results of analysis of the xylemsap of nodule-detached plants, it was concluded that the majorityof labelled carbon exported to the xylem stream from noduleswas in ureide form. A considerable amount of carbon was alsoreturned from roots to shoots via the xylem stream but it wasmore dependent on (non-labelled) carbon reserved in the roottissues. Key words: Soybean(Glycine max L.), root nodule, carbon partitoning, ¹³CO₂ assimilation, xylem     

Xylem Transport and Storage of Amino Acids by S.W. Australian Mistletoes and their Hosts

Amino acid composition of xylem (tracheal) sap and ethanolicextracts of shoots of mistletoes (Amyema spp. and Lysiana casuarinae)and their hosts were compared, using material collected in theirnative habitats. Data indicated that certain host xylem soluteswere transferred directly to the parasite xylem, while otherswere either not absorbed or were metabolized prior to transfer.Certain solutes were major constituents of parasite xylem, butundetected or only in trace amount in the host. Shoot aminoacid pools of parasites differed markedly from those of hosts.The mistletoe, Amyema preissii, exhibited differential storageand transport of arginine when parasitizing three differentspecies, but accumulated proline on only two of these hosts.Host- specific amino acids (djenkolic acid in Acacia saligna,and tyramine in Acacia acuminata) were transported and accumulatedin relatively large amounts by the parasite, but were not detectedin other associations. Proline was the major solute of Amyemalinophyllum parasitizing Casuarina obesa, but arginine predominatedin Lysiana casuarinae on the same host. However, when L. csuarinaeparasitized A. linophyllum, in turn parasitic on C. obesa, theLysiana accumulated equal amounts of proline and arginine andmore asparagine than when directly on the Casuarina. Xylem feedingof ¹⁵N-labelled aspartic acid or ¹³N-(amide labelled) asparagineto cut shoots or whole haustoria-bearing plants of the mistletoeA. preissii resulted in 68–73% of the ¹⁵N of aspartateand 24–30% of that of asparagine appearing in ethanol-solubleshoot amino compounds other than the fed solute. ¹⁵N labellingpatterns of detached shoots were not noticeably different fromthat of whole plants suggesting that the haustorium had relativelylittle effect on processing incoming solutes. Alanine, glutamine,and arginine were principal recipients of ¹⁵N from aspartate,alanine and glutamine in the case of fed asparagine. It is estimatedthat 24% of the carbon requirements for dry matter accumulationin Amyema linophyllm were met by intake of xylem sap solutesfrom its host Casuarina obesa. Key words: Amino acids, xylem transport, mistletoes, host: parasite relations, N metabolism     

In Vitro Phosphorylation of Proteins in IAA-Treated Mesocotyls in Zea mays

Five-mm sections of elongation zones of Zea mesocotyls wereincubated for designated periods with various concentrationsof IAA. In vitro protein phosphorylation in the soluble fraction(85,000 x g supernatant) prepared from the sections was analyzedby sodium dodecyl sulfate-polyacrylamide gel electrophoresis.The phosphorylation of proteins in the soluble fraction thathad been prepared from sections incubated for 20 min in thepresence of 10{small tilde}^s M IAA was greater than that inthe sections incubated for 20 min without IAA. The amount ofphosphorylation of proteins per protein became higher when higherconcentrations increased (10{small tilde}⁸—10{small tilde}⁵M).The growth of sections incubated in the presence of 10{smalltilde}⁸ M IAA or higher concentrations was greater than thatof sections incubated in the absence of IAA. The promotion ofgrowth by IAA was greater at higher concentrations of IAA. Proteinsin the soluble fraction, prepared from sections incubated for20 min in the presence of 10{small tilde}⁵ M IAA, were phosphorylatedin the presence of either 10 fM cAMP, 10 µM cGMP, 100µM W-7, 100 µM W-5, 20 µM H-7 or 20 µMHA1004. The calmodulin antagonist, W-7, and the inhibitor ofprotein kinase C, H-7, inhibited the phosphorylation of proteinsstimulated by incubation with IAA. These results suggest thatIAA promotes cell elongation via protein phosphorylation thatdepends on calmodulin-dependent protein kinase and protein kinaseC. (Received November 29, 1995; Accepted May 20, 1996)     

Collection and Chemical Composition of Pure Phloem Sap from Zea mays L.

Pure phloem sap was collected from leaf sheaths of Zea maysL. by the insect laser technique, and its chemical compositionwas analyzed. Sucrose was the only sugar detected. The predominantinorganic ions were K⁺ and Cl^–. The adenylate energy chargeof phloem sap was between 0.72 and 0.86. (Received October 18, 1989; Accepted May 11, 1990)