Activities of Hydrogen Peroxide-Scavenging Enzymes in Germinating Wheat Seeds

During imbibition and germination of wheat (Triticum aestivum)in the dark over 72 h, activities of the enzymes of the ascorbate(AsA)-dependent H₂O₂-scavenging pathway, AsA peroxidase, monodehydroascorbate(MDAsA) reductase, dehydroascorbate (DHAsA) reductase and glutathione(GSSG) reductase as well as superoxide dismutase (SOD), catalaseand guaiacol peroxidase were determined both in whole grainsand in isolated embryos and endosperm. With the exception of DHAsA reductase, activities of the otherenzymes assayed increased in germinating seeds, especially duringradicle emergence (between 24–48 h of imbibition). Theseincreases, particularly for AsA peroxidase, were much higherin the embryo than in the endosperm. Within 72 h of imbibition,activities per seed increased 116-fold for AsA peroxidase, 19-foldfor guaiacol peroxidase, 5-fold for catalase and only 1·4-foldfor SOD. In contrast to the decreases in DHAsA reductase, theother AsA recycling enzyme, MDAsA reductase, increased 5-foldwithin 72 h. The results indicate that, in wheat seeds, imbibition and germinationis associated with enhanced cellular capacity to detoxify H₂O₂.For this detoxification the operation of AsA peroxidase togetherwith the AsA-regenerating enzymes appears to be of particularimportance. Key words: Ascorbate peroxidase, germination, hydrogen peroxide detoxification, inhibition, wheat     

Formation of Isodityrosine by Peroxidase Isozymes

Fry, S. C. 1987. Formation of isodityrosine by peroxidase isozymes.—J.exp. Bot. 38: 853–862. Tyrosine residues of extensin are oxidatively coupled in vivoto form isodityrosine bridges, whereas treatment of purifiedextensin with H₂O₂+ peroxidase in vitro yields only dityrosine.Two explanations for the correct mode of coupling in vivo weretested. The first, that the pH of the cell wall is lower thanthat (pH 9-0) at which in vitro experiments have been conducted,provided part of the answer since treatment of L-tyrosine withH₂O₂+peroxidase in vitro at pH 37–5 yielded some isodityrosine.The second, that the wall contains other isozymes of peroxidasethan the basic isozyme usually studied in vitro, appeared unlikelybecause several sharply contrasting isozymes yielded similarisodityrosine: dityrosine ratios from L-tyrosine+ H₂O₂ at anygiven pH. The isozymes were also similar in their ability tooxidize tyrosine-dimers further to higher polymers. It is concludedthat the formation of isodityrosine in vivo is dictated by neighbouringwall molecules, possibly ionically-bound pectins, which modifythe local environment of the tyrosine residues of extensin. Key words: Isodityrosine, peroxidase isozymes, extensin     

Rm Differences in Leaf Malate Dehydrogenases of Flax (Linum usitatissimum) Genotrophs: Apparent Developmental Effects

Fieldes, M. A. and Gray, T. J. 1988. R_m differences in leafmalate dehydrogenases of flax (linum usitatissimum) genotrophs:apparent developmental effects.—J. exp. Bot. 39: 499–509. Malate dehydrogenase (MDH) isozyme relative mobility (R_m) wasexamined in leaf extracts of Durrant's large (L) and small (S)flax genotrophs. Within both L and S there were differencesin R_m between leaves sampled from different positions down themain stem and between leaves sampled from plants of differentages. For leaves sampled from plants which were at the onsetof flowering, the R_m differences from the apex to the base ofthe stem showed similar trends in L and S. However, the neteffect of the trend for L was a linear increase in R_m from apexto base, which did not occur in S. The changes in R_m which occurredin apical leaves as the plants aged were also different in Land S; R_mdecreased in L and increased in S during the growthperiod just prior to flowering. The possible relationship betweenthese differences in the changes in MDH R_m within L and S, previouslyreported differences in the changes in peroxidase (PER) isozymeR_m and the morphological/developmental differences between Land S is discussed. In addition, the experimentation demonstratedthat ‘negative’ bands detected in MDH-stained gelsunder certain staining conditions appear to correspond to PERisozymes and effectively mean that PER and MDH isozyme R_m'scan be obtained from the same electrophoretic gels. Key words: Malate dehydrogenase, peroxidase, relative mobility, flax     

Antioxidant Defences under Hyperoxygenic and Hyperosmotic Conditions in Leaves of Two Lines of Maize with Differential Sensitivity to Drought

The effects of hyperoxygenic and hyperosmotic stress on severalaspects of antioxidant defences were studied in the leaves ofa drought-sensitive (LG11) and a drought-tolerant (LIZA) lineof maize (Zea mays L.). When leaf disks were subjected to theseverest stress conditions (100% O₂ and 0.5 M mannitol), theactivities of antioxidant enzymes, such as superoxide dismutase(SOD), catalase (Cat), ascorbate peroxidase (Asc-Px) and glutathionereductase (GSSG-Red), remained higher in disks of LIZA thanin disks of LG11. The ratios of activities of SOD to Cat, SODto Asc-Px and SOD to GSSG-Red were much higher in leaf disksfrom LG11 than in those from LIZA. Damage, as indicated by,for example, the extend of lipid peroxidation, the destructionof chlorophyll and carotenoids, the decrease in levels of proteinsulfhydryl groups and the leakage of electrolytes from cellswas apparent in leaf disks of both LIZA and LG11 as consequenceof the applied stresses. However, the damage was less markedin LIZA than in LG11. (Received September 2, 1992; Accepted July 20, 1993)     

Developmental and Biochemical Regulation of 'Constitutive' Nitrate Reductase Activity in Leaves of Nodulating Soybean

The developmental profile of ‘constitutive’ nitratereductase activity (cNRA) in leaves of soybean (Glycine max(L.) cv. Bragg) plants at different ages is described. The youngestleaves had most cNRA and the activity dropped off as a newerleaf developed above it. Each leaf had its distinct active periodof in vivo cNRA. This pattern was different in urea-grown andsymbiotically-grown plants (inoculated with Bradyrhizobium japonicumstrain USDA 110), where the latter had no detectable in vivocNRA in older leaves. Urea-grown plants maintained considerablein vivo NRA in such older leaves. When symbiotically-grown plantshad their nodules removed, in vivo cNRA reappeared in olderleaves within 1 d of removal, nearly reaching levels of youngleaves at 3 d after nodule excision. Allantoic acid (ALL), oneof the known transport ureides of soybeans, was implicated asa possible signal molecule from nodules to leaves. Allantoicacid (100 µM) inhibited in vitro c₁ NRA significantly,with 400 µM ALL resulting in complete inhibition. In contrast,allantoin (ALN) had no inhibitive effect on NRA. Inhibitionof c₁NRA by ALL was by a competitive process, judging from Lineweaver-Burkeplots against nitrate. Kinetics showed a constant Vmax of around105 nmol NO₂ mg^–1 protein h^–1 and a K_m for nitrateof 15 mM, which increased to 60 mM in the presence of 200 µMallantoic acid. Non-specific (ionic and pH-related) influenceswere eliminated. Allantoic acid also had a slight stimulatingeffect of in vitro NRA (up about 25% at 400 µM). Thesefindings suggest that c1NRA may be involved in ureide metabolism,rather than in vivo nitrate metabolism. Key words: Root-shoot interaction, nitrogen metabolism, nodulation, symbiosis     

Carbon Dioxide Fixation and Ribulose-1, 5-bisphosphate Carboxylase Activity in Intact Leaves of Sugar Beet Plants Exposed to Salinity and Water Stress

The influence of salinity in the growing media on ribulose-1,5-bisphosphate (RuBP) carboxylase and on CO₂ fixation by intactsugar beet (Beta vulgaris) leaves was investigated. RuBP carboxylase activity was mostly stimulated in young leavesafter exposure of plants for 1 week to 180 mM NaCl in the nutrientsolution. This stimulation was more effective at the higherNaHCO₂ concentrations in the reaction medium. Salinity also enhanced CO₂ fixation in intact leaves mostlyat rate-limiting light intensities. A 60 per cent stimulationin CO₂ fixation rate was obtained by salinity under 450 µEm^–2 s^–1. At quantum flux densities of 150 µEm^–2 s^–1 (400–700 nm) this stimulation was280 per cent. Under high light intensities no stimulation bysalinity was found. In contrast, water stress achieved by directleaf desiccation or by polyethylene glycol inhibited enzymeactivity up to fourfold at –1.2 MPa. Beta vulgaris, sugar beet, ribulose-1, 5-bisphosphate carboxylase, salt stress, water stress, carbon dixoide fixation, salinity     

Effect of Salinity on Growth, Nodulation and Nitrogen Yield of Chickpea (Cicer arietinum L.)

Chickpea cultivar ILC 482 was inoculated with salt-tolerantRhizobium strain Ch191 in solution culture with different saltconcentrations added either immediately with inoculation or5 d later. The inhibitory effect of salinity on nodulation ofchickpea occurred at 40 dS m^–1 (34.2 mol m^–3 NaCl)and nodulation was completely inhibited at 7 dS m^–1 (61.6mol m^–3 NaCl); the plants died at 8 dS m^–1 (71.8mol m^–3 NaCl). Chickpea cultivar ILC 482 inoculated with Rhizobium strain Ch191^spcstrwas grown in two pot experiments and irrigated with saline water.Salinity (NaCl equivalent to 1–4 dS m^–1) significantlydecreased shoot and root dry weight, total nodule number perplant, nodule weight and average nodule weight. The resultsindicate that Rhizobium strain Ch191 forms an infective andeffective symbiosis with chickpea under saline and non-salineconditions; this legume was more salt-sensitive compared tothe rhizobia, the roots were more sensitive than the shoots,and N₂ fixation was more sensitive to salinity than plant growth. Key words: Cicer arietinum, nodulation, N₂ fixation, Rhizobium, salinity     

The Rate of Photosynthesis in Isolated Chloroplasts

Chloroplasts were isolated using aqueous and nonaqueous procedures.Aqueous chloroplasts lost approximately 50 per cent, of theirsoluble proteins during isolation. Nonaqueous chloroplasts retainedall their soluble enzymes, but lost their ability to performthe light reactions of photosynthesis. It was possible to reconstitutea chloroplast system of higher activity by adding soluble enzymesfrom nonaqueous chloroplasts to protein-deficient aqueous chloroplasts.The properties of the reconstituted chloroplast system wereas follows: 1. The CO₂ fixation rate of the reconstituted chloroplast system( 4 µM./. chlorophyll/hr.) was 3–4 times that ofthe aqueous chloroplasts ( I µM./. chlorophyll/hr.). Thefixation of aqueous chloroplasts isapparently limited in partby lack of soluble enzymes. 2. During light-fixation, the reconstituted chloroplast systemaccumulated PGA. This indicates that the reduction of PGA totriosephosphate is a rate-limiting step in this system. 3. It was possible to increase the CO₂ fixation to 12 µM.CO₂/mg. chlorophyll/ hr. by addition of ATP and TPNH to thesystem, but the reduction of PGA was still rate-limiting. 4. Further increase in the fixation rate was obtained by concentratingthe reaction mixture. Part of the striking differences of theCO₂-fixing capabilities of chloroplasts in vivo and in vitrois caused by dilution effects. Extrapolation of the dilutioneffect to the protein concentration which exists in chloroplastsyields a CO₂ fixation rate of approximately 30 µM./mg.chlorophyll/hr. 5. Inhibitors which are located in vivo outside the chloroplastsaffect the CO₂ fixation in vitro. 6. Under consideration of the examined factors which influencethe CO₂ fixation of isolated chloroplasts, it is possible toraise the fixation from approximately 1 per cent, to at least15 per cent, of the fixation in vivo.     

Evidence for Involvement of the Superoxide Radical in the Conversion of 1-Aminocyclopropane-1-Carboxylic Acid to Ethylene by Pea Microsomal Membranes

Electron spin resonance (ESR) spectroscopy has provided evidencefor involvement of the superoxide anion (O₂^–) radicalin the conversion of l-aminocyclopropane-l carboxylic acid (ACC)to ethylene by microsomal membranes from etiolated pea seedlings.Formation of ethylene from ACC by the membrane system is oxygen-dependent,heat denaturable, inhibited by the radical scavenger n-propylgallate and sensitive to superoxide dismutase (SOD) and catalase.Addition of 1,2-dihydroxybenzene-3,5-disulfonic acid (Tiron)to the reaction mixture results in formation of the Tiron semiquinone(Tiron radical) ESR signal derived from O₂^–, and alsoinhibits ethylene production. The radical signal is oxygen-dependentand inhibited by SOD and catalase, but is formed both in thepresence and absence of ACC. Heat denaturation of the microsomalenzyme system completely blocks formation of the radical signal.The data collectively suggest that O₂^– generated by amembrane-bound enzyme facilitates the conversion of ACC to ethylene. (Received September 8, 1981; Accepted January 19, 1982)     

Partial Reduction in Activities of Photorespiratory Enzymes in C3-C4 Intermediates of Alternanthera and Parthenium

The maximum catalytic activities of several photorespiratoryand photosynthetic enzymes were determined in leaf extractsof three C₃–C₄ intermediates (Alternanthera ficoides,A. tenella and Parthenium hysterophorus) and were compared tothose of C₃ (A. sessiles, Pisum sativum) and C₄ (A. pungens,Zea mays and Amaranthus hypochondriacus) species. The activitylevels of key photorespiratory enzymes, glycolate oxidase, catalase,NADH-hydroxypyruvate reductase and glycerate kinase were less(28 to 35% reduced) in intermediates than those of typical C₃species. Similarly, the activities of photorespiratory aminotransferasesin the C₃–C₄ intermediates were also partially reduced(23 to 37% reduction). The activities of phosphoenolpyruvatecarboxylase (PEPC), pyruvate, orthophosphate dikinase and NAD-malicenzyme were higher (2 to 7 times) in leaf extracts of the intermediatesthan those of C₃ species. But the ratios of PEPC/rubisco inthe C₃–C₄ intermediates were more like C₃ than C₄ species.We draw attention to the partial reduction in enzyme activityof photorespiratory metabolism, which could be an importantfactor for restriction of photorespiration in the C₃–C₄intermediate species, in addition to enzyme compartmentationand/or operation of a ‘C₄-like’ cycle Key words: C₃–C₄ intermediates, C₄ pathway, enzyme profile, glycolate metabolism, photorespiration, photosynthesis     

Factors Influencing Alanine Aminotransferase Activity in Leaves of Lolium temulentumL.: II. EFFECTS OF GROWTH REGULATORS AND PROTEIN BIOSYNTHESIS INHIBITORS

Effects of kinetin (K), gibberellin A₃ (GA₃), and 2-(chloroethyl)-trimethylammoniumchloride (CCC) on levels of alanine aminotransferase (GPT) andrates of protein synthesis were studied with both intact plantsand isolated leaf segments of Lolium temulentum L. In intactplants CCC stimulated and CA₃ reduced GPT activity, the effectsbsing much greater in 8.h than in 16-h photoporiods. CCC showedmaximum stimulatory effects at 10^–2 M and K at 5 x 10⁵M. No effect of GA₃ could be demonstrated with concentrationsup to 10^–4M. Both K and CCC retarded GPT decline in leafsections, the latter without associated effects upon pigmentbreakdown. Cycloheximide was highly effective in reducing proteinsynthesis in leaf sections. A close correlation between rateof protein synthesis and GPT activity was found over an inhibitorconcentration range from 10^–6 to 10^–4 M. The resultsare discussed in terms of possible methods of in vivo regulationof GPT activity.     

Changes in the growth rates of saline-lake diatoms in response to variation in salinity, brine type and nitrogen form

The growth rates of four saline-lake diatom taxa were measuredunder varying conditions of salinity (5, 8 and 11), brine type(sulfate- versus bicarbonate-dominated) and nitrogen form (NH₄⁺versus NO₃^–), using a full factorial design. With NO₃^–as the nitrogen source, Cyclotella quillensis, Cymbella pusillaand Anomoeoneis costata exhibited lower growth rates in thesulfate versus bicarbonate media. The strain of Chaetoceroselmorei used in these experiments, isolated from a sulfate-dominatedlake, was unable to grow on NO₃^– alone. In the NH₄⁺ treatments,neither salinity nor brine type affected the growth rates ofC.quillensis or C.elmorei. When supplied with NH₄⁺, C.pusillaand A.costata had higher growth rates in the bicarbonate versussulfate media, although for C.pusilla the difference on NH₄⁺was not as great as on NO₃^–. The impact of brine typeon NO₃^– use is consistent with the theory that sulfateinhibits molybdate uptake, as molybdenum is required for NO₃^–use but not NH₄⁺. Cymbella pusilla was the only taxon affectedby changes in salinity. The four taxa used in these experimentsare frequently found in saline lakes and saline-lake sediments,hence they are used in paleoclimate reconstructions; the resultspresented here provide additional information that may enhancethese diatom-based reconstructions.     

A Comparison of the Growth, Photosynthesis, Stomatal Conductance and Water Use Efficiency of Moricandia and Brassica Species

When grown in pots and well-watered, the relative growth ratesof the above ground parts of two species of Moricandia (M. arvensis,an intermediate C₃–C₄ species, and M. moricandioides,a C₃ species) were inferior to those of two cultivated Brassicaspecies (B. campestris and B. napus). The Moricandia specieshad thicker leaves (greater d.wt per unit leaf area) with morechlorophyll than the Brassica species and had slightly greaterrates of photosynthesis per unit leaf area at an irradiance(400–700 nm) of 2000 µmol quanta m^–2 s ^–1.Leaves of M. arvensis, known to have a CO₂ compensation pointbetween that of C₃ and C₄ species, had a lower ratio of theintercellular to atmospheric partial pressure of CO₂ (C₁/C_a)and a greater instantaneous water use efficiency (WUE) thanthose of M. moricandioides and the Brassica species. Carbon isotope discrimination (     

Effects of a Plant-Growth Regulator, Prohexadione, on the Biosynthesis of Gibberellins in Cell-Free Systems Derived from Immature Seeds

Inhibition of the biosynthesis of gibberellins by prohexadione,3,5-dioxo-4-propionylcyclo-hexanecarboxylic acid, was studiedwith cell-free systems derived from immature seeds of Cucur-bitamaxima, Phaseolus vulgaris and Pisum sativum. Prohexadione,at a concentration of 10–⁴ M, inhibited C-7 oxidationof GA₁₂-aldehyde, C-20 oxidation of GA₁₅, conversion of C₂₀-gib-berellinsto C₁₉-gibberellins, 3ß-hydroxylation, 2,3-dehydrogenationof GA²⁰, 2,3-epoxidation of GA₅ and 2ß-hydroxylationof GA₉ and GA₂₀. The 3ß-hydroxylase activity appearedto be more sensitive to prohexadione than were the C-20 oxygenaseand the 2ß-hydroxylase activities. The conversionof mevalonic acid to GA₁₂-aldehyde and the 13-hydroxylationof GA₁₂ were not affected by prohexadione at a concentrationof 3 ? 10^–4 M. All of the steps inhibited by prohexadioneare oxidation steps catalyzed by soluble enzymes that require2-oxoglutarate, Fe²⁺ and oxygen, and all of them occur distalto the synthesis of GA₁₂-aldehyde in the biosynthesis of gibberellins. (Received April 4, 1990; Accepted September 14, 1990)     

Effects of Some Growth Regulators and Benzoic Acid Derivatives on Flower Initiation and Root Elongation of Pharbitis nil, Strain Kidachi

Seedlings of Pharbitis nil, strain Kidachi, were grown undercontinuous light at 20°C in vessels containing 5,000-mlnutrient solution, 24 plants per vessel. NAA (0.005–0.5µM), GA₃ (0.1–0.5 µM), kinetin (0.5–5µM), benzyladenine (0.05–5 µM) or abscisicacid (4 µM) added to the nutrient solution induced long-dayflowering, and the flowering was always accompanied by suppressionof root elongation. 3,4-Dichlorobenzoic acid (0.05–10µM) and some other benzoic acid derivatives which arehighly effective for the induction of flowering in Lemna paucicostataalso showed similar effects. Neither NAA, kinetin nor 3,4-dichlorobenzoicacid applied via the apical part of the hypocotyl could causeflowering or suppression of root elongation. Thus, the flower-inducingeffect of the above substances was presumed to be secondaryto the suppression of root elongation. Ethrel (1–50 µM)added to the nutrient solution suppressed root elongation, butdid not induce flowering probably because it has flower-inhibitingactivity. ¹ This paper is dedicated to the memory of Dr. Joji Ashida,the first president of the Japanese Society of Plant Physiologists. (Received December 15, 1982; Accepted February 25, 1983)     

Preliminary characterization of 1-aminocyclopropane-1-carboxylate oxidase properties from embryonic axes of chick-pea (Cicer arietinum L.) seeds

For a deeper understanding of the germination of chick–pea(Cicer arietinum) seeds, which is dependent upon ethylene synthesis,a crude extract containing authentic ACC oxidase (ACCO) activitywas isolated in soluble form from the embryonic axes of seedsgerminated for 24 h. Under our optimal assay conditions (200mM HEPES at pH 7.0, 4µM FeS0₄, 6 mM Na–ascorbate,1 mM ACC, 20% 0₂, 3% CO₂ , and 10%glycerol) this enzyme was5–fold more active than under the conditions we used initiallyin the present work. The enzyme has the following K_m: 28 µMfor ACC (approximately 4–fold less than in vivo), 1.2%for O₂ (in the presence of an optimal CO₂ concentration of 3%),and 1% for CO₂ in the presence of O₂ (20%). The enzyme is inhibitedby phenanthroline (PNT) (specific chelating agent of ferrousion), and competitively inhibited (K₁, =0.5 mM) by 2–aminoisobutyricacid (AIB), and the enzymatic activity was not detectable inthe absence of CO₂. Under optimal assay conditions, the enzymehas two optimum temperatures (28 C and 35 C) and is inhibitedby divalent metal cations (Zn²⁺> CO²⁺>Ni²⁺>Cu²⁺>Mn²⁺>Mg²⁺) and by salicylic acid, propylgallate, carbonyl cyanidem–chlorophenyl hydrazone (CCCP), dinitrophenol (DNP),and Na–benzoate. The in vitro ACCO activity which we recoveredin soluble form is equivalent to approximately 80–85%of the apparent activity evaluated in vivo. Key words: ACC oxidase, Cicer arietinum, ethylene, germination, seeds     

Effects of temperature, salinity and food level on the life history traits of the marine rotifer Synchaera cecilia valentina, n. subsp.

A strain of the marine rotifer Synchaeta cecilia valentina,n. subsp., isolated from the Hondo of Elche Spanish Mediterraneancoastal lagoon at 22 salinity, was cultured in the laboratoryin 20 ml test tubes and fed with the alga Tetrasemis suecica.The effect of two temperatures (20 and 24°C), four salinities(20,25,30 and 37) and two food levels (15 000 and 25000 cellsml^–1) on the life history traits of this rotifer werestudied in life tables performed with replicated individualcultures. Temperature and salinity had a significant negativeeffect (P < 0.001) on the average lifespan (LS) and on thenumber of offspring per female (R₀) The effect of food levelon LS is unclear, whereas R₀ is greater at 20°C with thelower concentration of algae and at 24°C with the higheralgal concentration. The maximum values of LS and R₀, 5.6 daysand 9.2 offspring per female, respectively, were recorded at20°C, 25o salinity and low food concentration. There isalso a clear negative effect on the intrinsic growth rate (r)due to salinity. The effect of temperature depends on the foodlevel and, as occurs with R₀ the maximum values of r occur withthe lower algal concentration at 20°C, whereas at 24°Cthey are obtained with the higher algal concentration. Theser values, from 1.04 to 1.10 day^–1, were reached at 24°C,salinities of 20–25 and with high food concentration.     

The Biological Properties of Cyclopenin and Cyclopenol

Cyclopenin (C₁₇H₁₄O₃N₂) and cyclopenol (C₁₇H₁₄O₄N₂), isolatedfrom an abberent strain of Penicillium cyclopium (NRRL 6233),significantly inhibited the growth of etiolated wheat (Triticumaestivum) coleoptile segments. The former inhibited at 10^–3and 10^–4 M, the latter at 10^–3 M. Cyclopenin producedmalformation of the first set of trifoliate leaves in bean (Phaseolusvulgaris) at 10^–2 M and necrosis and stunting in corn(Zea mays) at 10^–2 M. Cyclopenol induced no apparent effectsin bean or corn plants. Neither compound changed the growthor morphology of tobacco (Nicotiana tabacum) plants. Cyclopenininduced intoxication, prostration and ataxia in day-old chicksat 500 mg/kg, but they recovered within 18 hours. Cyclopenolwas inactive against chicks when dosed at levels up to 500 mg/kg. (Received October 11, 1983; Accepted December 15, 1983)     

Salt Tolerance in the Halophyte Suaeda maritima L. Dum. Growth, Ion and Water Relations and Gas Exchange in Response to Altered Salinity

Clipson, N. J. W. 1987. Salt tolerance in the halophyte Suaedamaritima L. Dum. Growth, ion and water relations and gas exchangein response to altered salinity.—J. exp. Bot. 38: 1996–2004. Shoot and root fresh and dry weights and shoot sodium, chlorideand potassium contents were measured and shoot relative growthrates calculated in seedlings of Suaeda maritima over a periodof 11 d following a raising of culture solution salinity from0 to 200 mol m₃– NaCl. Growth, growth rates and sodiumand chloride contents, as compared to plants growing in theabsence of salt were increased whilst potassium contents declined.Shoot sodium accumulation rate and the rate of transport ofsodium from root to shoot, osmotic potential, and rates of photosynthesisand transpiration were also measured for up to 72 h after transferof plants originally growing at 0 and 200 mol₃– NaCl to200 and 400 mol m₃– NaCl respectively. Ion uptake andtransport rates were maximal 6-12 h after transfer and thendeclined to new steady-state levels within 48 h; osmotic potentialswere lowered over a 72 h period on average by approximately1·0 MPa; and after 9 h photosynthetic and transpirationrates were reduced by about 20percnt; and 30% respectively.Results are discussed in terms of the ability of halophytesto adjust to fluctuating salinity and to salt tolerance mechanismsin general. Key words: Suaeda maritima, salinity, gas exchange, growth, ion and water relations     

Quantitative Determination of a Peanut Anionic Peroxidase by Specific Monoclonal Antibodies

A monoclonal antibody (46-12-C12) for use in a solid-phase enzyme-linkedimmunosorbent assay (ELISA) specific for an anionic peroxidase(APRX) from peanut (Arachis hypogaea L.) suspension cell mediumwas developed. The McAb (IgG₁) had a high affinity (2.77 ? 10¹¹)and specificity for APRX, and showed only weak interaction witha-amylase and virtually no reactivity with other enzymes, suchas MCPRX (peanut), minor CPRX (peanut), peroxidase (horseradish),RuBP case (spinach), -glucosidase (rice), ß-glucosidase(almonds), acid phosphatase (potato), catalase (bovine liver)and glucose-6-phosphatase (yeast). Sample dilution curves werefound to parallel the standard curve. The detection limit was0.002 ? 10^–12 mol APRX. The absorbance was linear at concentrationsbetween 0.004–24 ? 10^–12 mol APRX. Three hundredsamples could be analysed per day by one person, with a semi-automaticperformance. Using this assay, levels of APRX have been determinedin a number of biological extracts of different origin. Key words: Peanut, anionic peroxidase, monoclonal antibody, enzyme-linked immunosorbent assay (ELISA)