Coordinate and Noncoordinate Changes in Enzyme Activities in Pentose Phosphate Cycle in Poplar: A Control of Enzyme Activities in Differentiated Xylem

Activities of glucose 6-phosphate and 6-phosphogluconate dehydrogenases,transketolase and transaldolase in twigs of Populus gelricawere measured throughout a year. In the living bark, activitiesof the four enzymes of the pentose phosphate cycle changed atabout the same time in the life cycle of the plant. In the differentiatingxylem cells there also occurred a simultaneous change in thefour enzyme activities. After differentiation of cambium toxylem, the high levels of the four enzyme activities fell graduallyand reached minimum levels by early September. In early September,the former two dehydrogenase activities began to rise again,while the latter two transferase activities continued to decrease.The elevated levels of the two dehydrogenases in the differentiatedxylem remained unchanged in the non-growing period of the lifecycle of the plant. Such a changing pattern of enzyme activitiesin the life cycle suggested that the pentose phosphate cyclein the differentiated xylem is interrupted in part at the stepof transketolase reaction, which results in an increased supplyof pentoses and NADPH. Moreover, these characteristic changesin the enzyme activities in the xylem are correlated with thechanges in the fine structures of the cells. ¹ Contribution No. 2272 from the Institute of Low TemperatureScience, Hokkaido University, Sapporo, Japan (Received June 26, 1981; Accepted September 28, 1981)     

Adenosine Triphosphate Levels in the Poplar during One Year of Growth

ATP concentrations in twigs of the poplar (Populus gelrica)were studied for one full year. During the wintering period,the living bark and xylem contained the same levels of ATP (about20 to 40 nanomoles per g dry weight). At the time of growthand enlargement, the xylem contained more ATP (about 80 to 230nanomoles per g dry weight) than did the bark (about 160 nanomolesper g dry weight). Values for the adenylate energy charge were stable, in the vicinityof 0.73 to 0.81, at about the time of the onset of active growthin May, and at the stage when the plant was almost ready forwintering in October or in late November. ¹ Contribution No. 2271 from the Institute of Low TemperatureScience, Hokkaido University, Sapporo, Japan (Received June 26, 1981; Accepted August 25, 1981)     

Increase in Enzyme Activities Related to Ascorbate Metabolism during Cold Acclimation in Poplar Twigs

Activities of ascorbate free radical reductase, ascorbate peroxidase,dehydroascorbate reductase, ascorbate oxidase and catalase inthe twigs of poplar, Populus gelrica, were measured throughouta year. Activity levels of the first three enzymes were highduring the wintering period of the life cycle, and the changesin the three enzyme activities occurred simultaneously. In fall,when the growth and enlargement of the tissues began to cease,the activities began to increase. In contrast to the activitiesof the above three enzymes, catalase activity began to increaseas the growth and enlargement proceeded, and the activity droppedby early November. Ascorbate levels in the twigs were measured,and the living bark and the xylem tissue were found to containsimilar levels of ascorbate (8 to 20 µmol and 2 to 14µmol per gram dry weight, respectively). From these results,it was suggested that in the growing period, deleterious H₂O₂produced in such organelles as the endoplasmic reticulum isdecomposed by catalase, and that in winter, oxidation and reductionreactions of ascorbate function not only to detoxify the peroxideproduced in the tissues, but also serve as a respiratory processto regenerate NADPH in the non-photosynthetic tissues of perennials. ¹Contribution No. 2624 from the Institute of Low TemperatureScience, Hokkaido University, Sapporo 060, Japan. (Received January 25, 1984; Accepted June 1, 1984)     

Occurrence of nicotinamide adenine dinucleotide phosphatelinked glyoxylate reductase in nonphotosynthetic xylem tissue of perennials

Xylem extracts of poplar tree contained glyoxylate reductase specific for NADPH. By isoelectric focusing in the pH ranges 3.5 to 10 or 4 to 6, the enzyme exhibited a single peak of activity at pH 5.4. The enzyme showed essentially no activity toward hydroxypyruvate, pyruvate, or NADH. The reaction was optimal at pH 6.0 in phosphate buffer and the activity profile exhibited a sharp and narrow pH profile with half-maximal velocities at about pH 7.0. The K_m of the enzyme for glyoxylate was 0.11 millimolar. The xylem tissue of poplar tree exhibited high levels of enzyme activity (30 micromoles per gram dry weight per hour) even in the wintering stage and a slight change in activity occurred in spring and fall at the time when metabolism transition occurs.     

Glycolate and glyoxylate metabolism in HepG2 cells

Oxalate synthesis in human hepatocytes is not well defined despite the clinical significance of its overproduction in diseases such as the primary hyperoxalurias. To further define these steps, the metabolism to oxalate of the oxalate precursors glycolate and glyoxylate and the possible pathways involved were examined in HepG2 cells. These cells were found to contain oxalate, glyoxylate, and glycolate as intracellular metabolites and to excrete oxalate and glycolate into the medium. Glycolate was taken up more effectively by cells than glyoxylate, but glyoxylate was more efficiently converted to oxalate. Oxalate was formed from exogenous glycolate only when cells were exposed to high concentrations. Peroxisomes in HepG2 cells, in contrast to those in human hepatocytes, were not involved in glycolate metabolism. Incubations with purified lactate dehydrogenase suggested that this enzyme was responsible for the metabolism of glycolate to oxalate in HepG2 cells. The formation of ¹⁴C-labeled glycine from ¹⁴C-labeled glycolate was observed only when cell membranes were permeabilized with Triton X-100. These results imply that peroxisome permeability to glycolate is restricted in these cells. Mitochondria, which produce glyoxylate from hydroxyproline metabolism, contained both alanine:glyoxylate aminotransferase (AGT)2 and glyoxylate reductase activities, which can convert glyoxylate to glycine and glycolate, respectively. Expression of AGT2 mRNA in HepG2 cells was confirmed by RT-PCR. These results indicate that HepG2 cells will be useful in clarifying the nonperoxisomal metabolism associated with oxalate synthesis in human hepatocytes. liver; peroxisomes; hepatocytes; hyperoxaluria; alanine:glyoxylate aminotransferase; glyoxylate reductase     

Haustorium-related Uptake and Metabolism of Host Xylem Solutes by the Root Hemiparasitic ShrubSantalum acuminatum(R. Br.) A. DC. (Santalaceae)

Solute composition of root xylem sap of common native hostsof quandong (Santalum acuminatum) was compared with that ofcorresponding xylem sap and ethanolic extracts of endophytictissues of haustoria of the hemiparasite. Each host transporteda characteristic set of organic nitrogenous solutes, but littleor no nitrate, and the data indicated only limited direct flowof amino compounds between xylem streams of hosts and parasite.Proline predominated in the haustorium and xylem ofSantalum,but was at negligible levels in the xylem of most hosts. Sucrose,fructose, glucose, malate and citrate were at high levels inall saps, and fructose especially prominent inSantalum. Chloride,sulphate and phosphate were the principal inorganic anions ofthe xylem. Based on C:N ratios of xylem and dry matter ofSantalumandassuming a 70% or more dependence on the host for N, it wasestimated thatSantalumwould gain approximately one third ofits C requirement for dry matter production heterotrophicallyfrom the xylem of its hosts. Infiltration of xylem of haustoria-bearingroot segments of a major host (Acacia rostellifera) with a rangeof¹⁵N labelled substrates resulted in 40–80% of the¹⁵Nof endophytes of the attached haustoria being received as proline.Nitrate reductase activity was induced in haustoria followinghost xylem feeding of nitrate. The study concludes that haustoriaofSantalumact as a major site of synthesis and export of prolineand might therefore play an important role in osmotic adjustmentof the parasite and its related acquisition of water from hosts. Root hemiparasite; Santalum acuminatum; ¹⁵N labelled substrates; xylem transport; proline; osmoregulation     

The Possible Role of Potassium in the Activation of Axillary Buds of Bidens pilosus L. after Decapitation of the Apex: AN EXAMINATION BY X-RAY MICROANALYSIS

Growth of axillary buds in Bidens pilosus L. can be inducedby decapitation of the shoot apex. By means of X-ray microanalysisit is demonstrated that immediately after decapitation K⁺ isapparently accumulated in the stem tissue around the node. Conventionalelectron microscopy on sections of this part of the tissue revealedthat xylem parenchyma cells of those bundles that lead intothe cotyledons are differentiated as transfer cells. The possiblerole of K⁺ transport processes in growth initiation and regulationis discussed.     

The Distribution of Nitrate Assimilation Between Root and Shoot in Vicia faba L.

Nitrate assimilation was examined in two cultivars (Banner Winterand Herz Freya) of Vicia faba L. supplied with a range of nitrateconcentrations. The distribution between root and shoot wasassessed. The cultivars showed responses to increased applied nitrateconcentration. Total plant dry weight and carbon content remainedconstant while shoot: root dry weight ratio, total plant nitrogen,total plant leaf area and specific leaf area (SLA) all increased.The proportion of total plant nitrate and nitrate reductase(NR) activity found in the shoot of both cultivars increasedwith applied nitrate concentrations as did NO₃^–: Kjeldahl-Nratios of xylem sap. The cultivars differed in that a greaterproportion of total plant NR activity occurred in the shootof cv. Herz Freya at all applied nitrate concentrations, andits xylem sap NO₃^–: Kjeldahl-N ratio and SLA were consistentlygreater. It is concluded that the distribution of nitrate assimilationbetween root and shoot of V. faba varies both with cultivarand with external nitrate concentration. Vicia faba L., field bean, nitrate assimilation, nitrate reductase, xylem sap analysis     

Studies of Glycollate Utilization and Some Associated Enzymes of C1 Metabolism in the Endosperm of Ricinus communis L.

Glycollate metabolism in 5-day-old endosperm tissues of Ricinuscommunis L. was examined by feeding micromolar quantities of[2-¹⁴C]glycollate to tissue slices. It was found that glycollatecarbon was rapidly incorporated into glyoxylate, glycine, serine,and carbon dioxide. Only small amounts of ¹⁴C were incorporatedinto the sugars. Changes in the distribution of ¹⁴C with timesuggested that glyoxylate was a primary product and that glycineand serine were secondary products of glycollate metabolism.The results of feeding experiments are interpreted as indicatingthat a glycollate pathway leading to sugar biosynthesis is ofminor importance compared to the rapid utilization of glycollatefor the biosynthesis of glycine and serine. Enzymes necessaryto catalyse the incorporation of glycollate into glycine andserine have been examined in castor-bean endosperm extracts.These included: glycollic acid oxidase, gloxylic acid reductase,glyoxylate transaminase, N¹⁰ formyltetrahydrofolate synthetase,N⁵,N¹⁰-methylenetetrahydrofolate dehydrogenase, and serine hydroxymethyltransferase.     

NaCl Uptake in Roots of Zea mays Seedlings: Comparison of Root Pressure Probe and EDX Data

The extent by which salinity affects plant growth depends partlyon the ability of the plant to exclude NaCl. To study the uptakeof NaCl into excised roots of Zea mays L. cv. ‘Tanker’,two different techniques were applied. A root pressure probewas used to record steady state as well as transient valuesof root (xylem) pressure upon exposure of the root to mediacontaining NaCl and KCl as osmotic solutes. In treatments withNaCl, pressure/time responses of the root indicated a significantuptake of NaCl into the xylem. NaCl induced kinetics were completelyreversible when the NaCl solution was replaced by an isosmoticKCl solution. This indicated a passive movement of Na⁺-saltsacross the root cylinder. Root samples were taken at differenttimes of exposure to NaCl and prepared for X-ray microanalysis(EDX analysis). Radial profiles of ion concentrations (Na⁺,K⁺, Cl^–) were measured in cell vacuoles and xylem vesselsalong the root axis. Na⁺ appeared rapidly in mature xylem (earlymetaxylem) and living xylem (late metaxylem) before it was detectablein vacuoles of the root cortex. EDX results confirmed that thekinetics observed by the pressure probe technique correspondedmainly to an influx of Na⁺-salts into early metaxylem. In latemetaxylem, the uptake of Na⁺ was associated with a decline ofK⁺. The Na⁺/K⁺ exchange indicated a mechanism to reduce sodiumfrom the transpiration stream. Ion localization, ion transport, maize, root pressure, salinity, water relations, X-ray microanalysis, Zea mays     

Purification and properties of glyoxylate reductase I from baker's yeast.

The purification and properties of NADPH-linked glyoxylate reductase [EC 1. 1. 1. 79] from baker's yeast were studied. Two active fractions (peak I and peak II) were isolated by DEAE-cellulose column chromatography. The peak I fraction was purified to homogeneity by the criteria of disc gel electrophoresis and tentatively designated glyoxylate reductase I. Its molecular weight was calculated to be 31,000 from gel filtration measurements. The enzyme reduced glyoxylate 7 times faster than hydroxypyruvate and was specific for NADPH. The enzyme showed optimum activity between pH 5.5 and 7.2. The Michaelis constants for glyoxylate and NADPH were found to be 13 mM and 4 microM, respectively. The enzymic activity was not significantly affected by anions, except for nitrate and iodide, which were inhibitory.     

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     

Cyclic AMP in Rhizobia and Symbiotic Nodules

Cyclic adenosine 3',5'-monophosphate (cAMP) content of variouscultured rhizobia strains and tissues of legumes and non-leguminousplants was measured by enzyme immunoassays. Most rhizobia, culturedfor 44 to 165 h, contained cAMP ranging from 0.6 to 5 pmol mg^-1proteinexcept forAzorhizobium caulinodansORS571. The culture mediaalso contained varying amounts of cAMP depending on the strainof rhizobia.Azorhizobiumcells and their media contained no detectablecAMP. Nodules from most legumes and non-legumes had cAMP contentsranging from 2–70 pmol g^-1f.wt. However, nodules fromSesbaniarostrata,Crotalaria spectabilisandParasponia andersoniishowedundetectable cAMP levels, and those fromGlycine maxandVignaangularisoccasionally showed levels below the detection limit.The leaves of non-legumes mostly had cAMP levels below detectionlimit (approx. 1.0 pmol g^-1 f.wt), while the leaves ofa few legumes occasionally had detectable cAMP. The possiblerole of cAMP as a symbiotic signal is discussed. cAMP; legumes; modules; rhizobia; symbiosis     

Studies in Sieve-tube Exudation through Aphid Mouth-parts II. The Effects of Pressure Gradients in the Wood and Metabolic Inhibitors

Exudation was studied from the mouth-parts of the willow aphidTuberolachnus salignus (Gmelin) inserted in the phloem of isolated15 -cm. stem segments of Salix viminalis. By supplying waterunder pressure to the cut surface of the wood at one end ofa segment and allowing it to run freely from the other, a pressuregradient could be set up in the xylem. By closing the free end,the pressure in the xylem could be raised uniformly. This lasttreatment caused the rate of exudation to increase. This effectof pressure could be balanced by an equivalent osmoticum introducedinto the xylem. The increase was therefore due to the DPD inthe xylem rather than any intrinsic effect of pressure. The effect of a pressure gradient (4 atm. applied) dependedon the position of the mouth-parts in relation to the gradient.If they were near the low-pressure end, exudation from themincreased. If they were near the high-pressure end, exudationdecreased. In neither case was the total carbohydrate or totalnitrogen concentration of the exudate changed. When longer segments were used (e.g. 41 cm.) the effect of asimilar pressure (4 atm.) was greater than with 15-cm. segmentsalthough the point of application of the pressure was more remotefrom the mouth-parts. When the wood at the midpoint of a segmentwas severed leaving a narrow bridge of bark joining the twohalves, raising the pressure in the xylem of one half led toan increased exudation from mouth-parts situated in the otherhalf. Thus the effect of pressure was transmitted along thephloem since there was no rise in xylem pressure in the halfsegment bearing the mouth-parts. 10^-4 M. dinitrophenol applied to a bark abrasion a few centimetresaway from mouth-parts, reduced exudation. Applied to the cambialsurface, exudation was reduced by 0.1 per cent, phloridzin andstopped completely by 10^-4 M. dinitrophenol and 10^-6 M. potassiumcyanide. Inhibitors had no effect on the concentration of theexudate. No simple interpretation of the effects of pressure gradientsis possible, but it is suggested they give qualified supportto the Munch hypothesis.     

Purification and Characterization of Assimilatory Nitrate Reductase from the Cyanobacterium Plectonema boryanum

Assimilatory nitrate reductase (NR) was solubilized by acetonetreatment from Plectonema boryanum and was purified 7,700-foldby heat treatment, ammonium sulfate fractionation and chromatographyon DEAE-Sephacel and Sephadex G-150. Purified NR had a specificactivity of 85 µmol NO₂^– formed min^–1 mg^–1protein. The enzyme retained both ferredoxin (Fd)- and methylviologen (MV)-linked NR activities throughout the purificationprocedure. Molecular weight was 80,000. The pH optimum was 10.5in the MV-assay and 8.5 when assayed with enzymatically reducedFd as the electron donor. Apparent Km values for nitrate andMV were 700 µM and 2,500µM in the MVassay and 55µM and 75 µM for nitrate and Fd in the Fd-assay.The enzyme was inhibited by thiol reagents and metal-chelatingreagents. (Received October 1, 1982; Accepted March 8, 1983)     

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)     

SOME PROPERTIES OF SULFITE REDUCTASE FROM YEAST

The MVH- and NADPH-linked sulfite reducing activities were assayedin extracts obtained from a wild strain of Saccharomyces cerevisiaeand various auxotrophic mutants derived from it. All the extractspossessing the NADPH-linked activity also showed the MVH linkedactivity, and all those lacking the latter also lacked the former.However, extracts from several mutants had the MVH-linked activitywithout having the other. NADPH-sulfite reductase was purified nearly 200-fold from extractsof the wild strain. Throughout the purification steps, the MVH-linkedactivity was also purified in association with the NADPH-linkedactivity, and the ratio between the two remained essentiallyconstant. However, on exposure to heat, low ionic strengthsand PCMB, only the NADPH-linked activity was lost, leaving theMVH-linked activity almost unaffected. Both activities weresensitive to cyanide. The sulfite reductase could also reduce nitrite and hydroxylamine, and the nitrite- and hydroxylamine-reducing activitywas sensitive to the treatments which inhibited the NADPH-sulfitereducing activity. Addition of nitrite or hydroxylamine competitivelyinhibits the NADPH linked sulfite reduction. The enzyme alsoshowed diaphorase activity, reducing DPIP or MV. This activitywas inhibited by the treatments to which the NADPH-linked sulfitereduction was sensitive, but it was not sensitive to cyanide. A tentative schematic model for yeast sulfite reductase is presented. ( Accepted October 8, 1964)     

The Partitioning of Nitrate Assimilation Between Root and Shoot of a Range of Temperate Cereals and Pasture Grasses

Nitrate reductase activity (NRA, in vivo assay) and nitrate(NO^-₃) content of root and shoot and NO^-₃ and reduced nitrogencontent of xylem sap were measured in five temperate cerealssupplied with a range of NO^-₃ concentrations (0·1–20mol m^–3) and three temperate pasture grasses suppliedwith 0·5 or 5 0 mol m^–3 NO^-₃ For one cereal (Hordeumvulgare L ), in vitro NRA was also determined The effect ofexternal NO^-₃ concentration on the partitioning of NO^-₃ assimilationbetween root and shoot was assessed All measurements indicatedthat the root was the major site of NO3 assimilation in Avenasatwa L, Hordeum vulgare L, Secale cereale L, Tnticum aestivumL and x Triticosecale Wittm supplied with 0·1 to 1·0mol m^–3 NO^-₃ and that for all cereals, shoot assimilationincreased in importance as applied NO^-₃ concentration increasedfrom 1.0 to 20 mol m^–3 At 5.0–20 mol m^–3 NO3,the data indicated that the shoot played an important if notmajor role in NO^-₃ assimilation in all cereals studied Measurementson Lolium multiflorum Lam and L perenne L indicated that theroot was the main site of NO^-₃ assimilation at 0.5 mol m^–3NO^-₃ but shoot assimilation was predominant at 5.0 mol m^–3NO^-₃ Both NRA distribution data and xylem sap analysis indicatedthat shoot assimilation was predominant in Dactylis glomerataL supplied with 0.5 or 5.0 mol m^–3 NO^-₃ Avena sativa L., oats, Hordeum vulgare L., barley, Secale cereale L., rye, x Triticosecale Wittm., triticale, Triticum aestivum L., wheat, Dactylis glomerata L., cocksfoot, Lolium multiflorum Lam., Italian ryegrass, Lolium perenne L., perennial ryegrass, nitrate, nitrate assimilation, nitrate reductase activity, xylem sap     

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     

Purification and properties of two glyoxylate reductases from a species of Pseudomonas

1. Two enzymes that catalyse the reduction of glyoxylate to glycollate have been separated and purified from a species of Pseudomonas. Their molecular weights were estimated as 180000. 2. Reduced nicotinamide nucleotides act as the hydrogen donators for the enzymes. The NADH-linked enzyme is entirely specific for its coenzyme but the NADPH-linked reductase shows some affinity towards NADH. 3. Both enzymes convert hydroxypyruvate into glycerate. 4. The glyoxylate reductases show maximal activity at pH6·0–6·8, are inhibited by keto acids and are strongly dependent on free thiol groups for activity. 5. The Michaelis constants for glyoxylate and hydroxypyruvate were found to be of a high order. 6. The reversibility of the reaction has been demonstrated for both glyoxylate reductases and the equilibrium constants were determined. 7. The reduction of glyoxylate and hydroxypyruvate is not stimulated by anions.