Cross-linking of soluble extensin in isolated cell walls

The extensin component of primary cell walls has generally been considered to be an intrinsically insoluble cell wall glycoprotein. Recent data have established that cell wall extensin is in fact secreted in a soluble monomeric form which slowly becomes insolubilized in the cell wall probably through the oxidative formation of isodityrosine cross-links. We now show that isolated cell walls from aerated root slices of Daucus carota have the capacity to insolubilize extensin through the formation of isodityrosine. This in vitro cross-linking is specific for the extensin glycoprotein, as other wall proteins are not cross-linked by the isolated wall system. Although extensin can be cross-linked in solution by peroxidase and H₂O₂, dityrosine and not isodityrosine is the phenolic cross-link formed. Wall-catalyzed cross-linking of soluble extensin is inhibited by l-ascorbate, and both the initial rate and total extent of cross-linking are inhibited by acidic pH in the physiological range (pH 4 to 6). We suggest several mechanisms by which acid might inhibit cross-linking and propose that cytoplasmic factors (ascorbate and/or hydrogen ions) may regulate the solubility of extensin in vivo.     

Aluminium Effects on ATPase Activity and Lipid Composition of Plasma Membranes in Sugar Beet Roots

The effect of aluminium (Al) in vivo and in vitro on root plasmamembranes has been studied in two sugar beet (Beta vulgarisL.) cultivars, Monohill (Al-sensitive) and Regina (relativelyAl-tolerant). Although Al in vitro inhibited the MgATPase inan uncompetitive way for both cultivars raised in the absenceof Al, the specific K⁺-activation of the MgATPase was only inhibitedby Al in cv. Monohill. Arrhenius analysis of the MgATPase activity showed that theeffect of Al in vitro depended on whether or not the plantswere exposed to Al in vivo. Al treatment in vitro of the MgATPasefrom control plants cultivated at a low pH (5·4) causedan increase in the phase transition temperature from 17 to 22°C. Only at a higher pH range (pH 6·1) could a secondtransition temperature be induced (at 9 °C). By additionof Al in vitro to plants cultivated with Al at pH 5·4,the slopes of the activity plots did not change. Aluminium changedthe K_m of the ATPase for MgATP in an opposite way by treatmentin vivo and in vitro. Lipid analyses of the plasma membranes showed that the acylcomposition differed little following Al treatment in vivo,but that the ratio of phosphatidylcholine: phosphatidylethanolamineincreased. The changes correlated with the observed change inthe K_m for the MgATPase. We conclude that the main effect ofAl on the MgATPase is not due to the formation of an Al-ATPcomplex. Instead, Al may bind to the membrane-bound enzyme(s)and/or modify the lipid environment. Key words: Aluminium, ATPase, Beta vulgaris, lipids     

Characteristics of the Cl- Action Site in the O2 Evolving Reaction in PS II Particles: Electrostatic Interaction with Ions

The role of Cl^– in the reactivation of O₂ evolution inphotosystem II (PS II) particles derived from spinach chloroplastswas studied in the presence of various salts. Multivalent ion(especially anion) salts were found to strongly suppress thereactivation of O₂ evolution by Cl^– in the Cl^–-depletedPS II particles in a competitive manner. The effectiveness ofanions in the suppression of Cl^–-supported O₂ evolutionwas in the order of trivalent>divalent>monovalent ones.Multivalent anions similarly suppressed O₂ evolution in theuntreated PS II particles under low and moderate Cl^– concentrations.pH dependence of the Cl^–-affinity (K_m) value for Cl^–)was also studied. Within the pH range 5.5 to 8 the K_m valuebecame higher as the pH of the medium increased. These resultssuggest that the membrane surface in the vicinity of the Cl^–action site is net positively charged and attracts Cl^–electrostatically, and that the site is almost freely accessibleto various anions. The origin and role of the local net positivedomain and the role of peripheral proteins are discussed. (Received May 27, 1985; Accepted October 8, 1985)     

Localization and Properties of Cell Wall Enzyme Activities Related to the Final Stages of Lignin Biosynthesis

Cell wall activities which are related to the final stages oflignin biosynthesis, that is the generation of hydrogen peroxideand peroxidase activity, were investigated using biochemicaland histochemical methods. Peroxidases involved in both reactionsappeared to be restricted to lignifying tissues. Isolated cellwalls exhibited a very high affinity for syringaldazine. Cellwalls were able, in vitro as well as in vivo, to oxidize guaiacolin the absence of H₂O₂ when NADH was present in the incubationmedium together with p-coumarate and MnCl₂ as cofactors. Theorigin of the NADH used to form H₂O₂ is discussed. Key words: Lignin biosynthesis, Oxidative polymerization, Peroxidases     

Characterisation of Acidic and Basic Apoplastic Peroxidases from Needles of Norway Spruce (Picea abies, L., Karsten) with Respect to Lignifying Substrates

Acidic and basic peroxidases, termed as POD-A and POD-B, wereisolated from the apoplastic space of spruce (Picea abies, L.)needles and purified by acetone precipitation and anion exchangechromatography to apparent homogeneity. The molecular massesof POD-A and POD-B were 39.6 and 29.0 kDa, respectively. ThepH optimum of both isozymes ranged from 4.5 to 6. The apparentK_m values of POD-A and POD-B were 460 and 210 µM for coniferylalcohol. Both isozymes acted also as NADH oxidases with apparentK_m-values of 103 µM (POD-A) and 70 µM (POD-B). NAD⁺but not NADH was found in the apoplastic space of lignifyingneedles. Based on the lignification rate, the contents and kineticproperties of PODs, NADH oxidation by POD is not the major sourceof H₂O₂ required for lignin polymerisation. (Received December 21, 1996; Accepted March 3, 1997)     

Some Characteristics and Inhibitors of Indoleacetic Acid Oxidase from Tissue 2

Extracts from tissue cultures of crown-gall from Parthenocissuscatalysed the destruction of indoleacetic acid in vitro withoptimum activity at pH 4·5. The presence of two co-factors,Mn⁺⁺ and 2,4-dichlorophenol, was necessary for this activity,which was found to be strictly aerobic. Chlorogenic acid, caffeic acid, scopoletin, ferulic acid, andgibberellic acid markedly inhibited IAA-destruction. Chlorogenicacid inhibition was reversed by the addition of H₂O₂. Chlorogenicacid was not oxidized by the IAA-destroying system and did notbehave as a competitive inhibitor. The IAA-oxidase extract manifested peroxidase and phenolaseactivity with catechol and pyrogallol as substrates. However,this activity was greater at pH 7·0 than at the optimumfor IAA-oxidase activity, pH 4·5. Further evidence ofthe existence of these two enzymes in the intact tissue wasdemonstrated by histochemical studies. In tissue slices, peroxidaseactivity was very high and widely distributed while phenolaseactivity was low and restricted to localized centres of thetissue.     

Reactive oxygen species as causative agents in the ichthyotoxicity of the red tide dinoflagellate Cochlodinium polykrikoides

The underlying toxic mechanisms of the red tide dinoflagellate,Cochlodinium polykrikoides, were studied with respect to thereactive oxygen species-mediated toxic effect. Cochlodiniumpolykrikoides generates superoxide anion (O₂^–) and hydrogenperoxide (H₂O₂), as measured by the cytochrome c reduction methodand scopoletin–peroxidase method, respectively. The capabilityof C.polykrikoides to generate these oxygen radicals was relatedto the growth phase: the highest rate in the exponential phaseand a gradual decrease in the stationary phase. Other phytoplankton,such as Eutreptiella gymnastica, Heterosigma akashiwo, Prorocentrummicans, Gymnodinium sanguineum and Alexandrium tamarense, alsoproduce H₂O₂; the rate of H₂O₂ generation by these species waslower than that of C.polykrikoides. The exposure of liposomalsamples to intact or ruptured individuals of C.polykrikoidesresulted in severe membrane damage, such as liposomal lipidperoxidation. Cochlodinium polykrikoides-induced lipid peroxidationwas significantly reduced by oxygen radical scavengers, superoxidedismutase, benzoquinone, catalase and mannitol. In addition,lipid peroxidation of gill tissue of flatfish exposed to C.polykrikoidesincreased with increasing algal cell density. These resultssuggest that reactive oxygen species generated from C.polykrikoidesare responsible for oxidative damage leading to fish kills.     

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     

Oxidative stress decreases pHi and Na(+)/H(+) exchange and increases excitability of solitary complex neurons from rat brain slices

Putative chemoreceptors in the solitary complex (SC) are sensitive to hypercapnia and oxidative stress. We tested the hypothesis that oxidative stress stimulates SC neurons by a mechanism independent of intracellular pH (pH_i). pH_i was measured by using ratiometric fluorescence imaging microscopy, utilizing either the pH-sensitive fluorescent dye BCECF or, during whole cell recordings, pyranine in SC neurons in brain stem slices from rat pups. Oxidative stress decreased pH_i in 270 of 436 (62%) SC neurons tested. Chloramine-T (CT), N-chlorosuccinimide (NCS), dihydroxyfumaric acid, and H₂O₂ decreased pH_i by 0.19 ± 0.007, 0.20 ± 0.015, 0.15 ± 0.013, and 0.08 ± 0.002 pH unit, respectively. Hypercapnia decreased pH_i by 0.26 ± 0.006 pH unit (n = 95). The combination of hypercapnia and CT or NCS had an additive effect on pH_i, causing a 0.42 ± 0.03 (n = 21) pH unit acidification. CT slowed pH_i recovery mediated by Na⁺/H⁺ exchange (NHE) from NH₄Cl-induced acidification by 53% (n = 20) in -buffered medium and by 58% (n = 10) in HEPES-buffered medium. CT increased firing rate in 14 of 16 SC neurons, and there was no difference in the firing rate response to CT with or without a corresponding change in pH_i. These results indicate that oxidative stress 1) decreases pH_i in some SC neurons, 2) together with hypercapnia has an additive effect on pH_i, 3) partially inhibits NHE, and 4) directly affects excitability of CO₂/H⁺-chemosensitive SC neurons independently of pH_i changes. These findings suggest that oxidative stress acidifies SC neurons in part by inhibiting NHE, and this acidification may contribute ultimately to respiratory control dysfunction. hyperoxic hyperventilation; O₂ toxicity; pH regulation; brain stem; reactive oxygen species     

Thermal Dependence of Air Convection Requirement and Blood Gases in the Snake Coluber constrictor

In this report I discuss ventilatory and circulatory adjustmentsthat prov for increased O₂transport associated with increasedbody temperature in the snake Coluber constrictor. Also includedis the effect of temperature upon acid-base status. Minute ventilationincreases with rising body temperature but does not keep pacewith the increment in resting O₂ consumption. The decrease inair convection requirement (i.e., ventilation ÷ oxygenconsumption) causes lung pO₂ and arterial oxygen contentto falland lung pCO₂ to rise. With the rise in lung pCO₂, systemicarterial pCO₂ and H⁺; concentration increase while plasma bicarbonateconcentration does not change. The effect of temperature uponair convection requirement, arterial pCO₂, and pH are most pronouncedat body temperatures above about 27°C whereColuber behavesapproximately as an alphastat pH regulator. Despite the inverserelationship between temperature and lung pO₂, systemic arterialpO₂ is about 80 torr lower at 15°C than at 35°C. Thisdecline in arterial pO₂ as temperature falls is explained byleft shifting the oxygen dissociation curve in the presenceof aconstant right-to-left intracardiac shunt.     

A microsensor for direct measurement of O2 partial pressure within plant tissues3

Widespread use of O₂ microsensors to measure O₂ partial pressure(pO₂) in plant tissues has been limited in part because of difficultyof construction and other technical obstacles. By modifyingpublished techniques, an O₂ microsensor was constructed thatcombined the advantages of Clark-type microsensors with lesscomplicated construction techniques. The specifications andsome performance characteristics of the microsensor are: tipdiameter 1–5 µm; sensitivity 7.5–25 pA kPa^–1;negligible stir-induced current; response time 540 ms. The microsensorcan be used in air or solution, and each sensor can be usedfor several experiments. The sensitivity of the microsensorwas unchanged during measurements over the physiological rangeof pO₂ in intact, growing maize (Zea mays L.) primary roots,and was thus unaffected by cellular fluids and turgor pressure.Use of the microsensor to compare pO₂ profiles in vermiculite-and solution-grown roots is described. The O₂ microsensor couldfind application in studies in which information on tissue pO₂is needed, but for which conventional O₂ probes are too large. Key words: Oxygen microsensor, Zea mays L., roots, oxygen partial pressure     

Photosynthesis by Guard Cell Chloroplasts of Vicia faba L.: Effects of Factors Associated with Stomatal Movement

The properties of photosynthetic O₂ evolution by mesophyll cellchloroplasts (MCC) and guard cell chloroplasts (GCC) isolatedfrom protoplasts of Vicia faba L. have been studied and effectson O₂ evolution of factors known to regulate stomatal movementshave been compared. The O₂ evolution of GCC was CO₂-dependent.The saturating light intensity for O₂ evolution was between150 and 200 µmol m^–2s^–1 for MCC and was between400 and 1,000µmol m^–2s^–1 for GCC. Light quality(red vs. blue) had no significant effect on O₂ evolution byeither MCC or GCC. The O₂ evolution rate of MCC was stronglydependent on external K⁺ concentration, but GCC did not respondsignificantly to variations in external K⁺ concentration between0 and 250 mM. The optimal external pH for O₂ evolution by MCCwas approximately 7.5, and either higher or lower external pHsignificantly inhibited O₂ evolution. However, O₂ evolutionby GCC was only slightly enhanced when external pH was increasedfrom 6.0 to 8.0. Our observation of differential sensitivityof MCC and GCC to light intensity and to variations of cytoplasmicK⁺ and pH may indicate differential regulation of photosynthesisin MCC and GCC. ¹Current address: Biology Department, Pennsylvania State University,208 Mueller Laboratory, University Park, PA 16802, U.S.A.     

Extreme Phosphate Deficiency Decreases the In Vivo CO2/O2 Specificity Factor of Ribulose 1,5-Bisphosphate Carboxylase-Oxygenase in Intact Leaves of Sunflower

Sunflower plants were grown under controlled environmental conditionswith either 0 or 10 mol m^–3 phosphate (Pi). From steady-statemeasurements of gas exchange and chlorophyll fluorescence madeon intact leaves, the in vivo CO₂/O₂ specificity factor (invivo K_sp) of ribulose 1,5-Aisphosphate carboxylase-oxygenase(Rubisco) was determined following two methods based on modelsof C₃ photosynthesis by Brooks and Farquhar (1985) and Peterson(1989). The two methods gave in vivo K_sp values for controlsunflower leaves which were similar to published values forhigher plants. Extreme Pi deficiency decreased in vivo K_sp,in sunflower leaves compared to adequate Pi. This suggests thatPi deficiency affected photorespiration less than photosynthesis.The decrease in in vivo K_sp may be due to a real change in theenzyme kinetics favouring oxygenation more than carboxylationor due to an increase in the number of CO₂ molecules releasedper oxygenation; in which case the observed decrease in thein vivo K_sp determined on intact leaves will not agree numericallywith the true K_sp of Rubisco determined in vitro using purifiedenzyme from the same leaf. We discuss the implications of therelatively large photorespiration in Pi-deficient sunflowerleaves with respect to the increased dissipation of photosyntheticelectrons and photorespiratory recycling of Pi in thechloroplaststroma. Although our results on in vivo K_sp suggested a relativelylarger photorespiratory potential in Pi-deficient than controlsunflower leaves, photosynthesis was insensitive to O₂ in Pi-deficientleaves; the possible reasons for this phenomenon are discussed.Under extreme Pi deficiency, O₂ sensitivity of photosynthesisis not a reflection of the in vivo photorespiratory rates. Determinationof in vivo K_sp of Rubisco is a useful approach to study thephotorespiratory potential of intact leaves. Key words: Chlorophyll fluorescence, phosphate deficiency, photorespiration, photosynthesis, PSII quantum yield, Rubisco specificity factor     

Di-isodityrosine is the intermolecular cross-link of isodityrosine-rich extensin analogs cross-linked in vitro

Extensins are cell wall hydroxyproline-rich glycoproteins that form covalent networks putatively involving tyrosyl and lysyl residues in cross-links catalyzed by one or more extensin peroxidases. The precise cross-links remain to be chemically identified both as network components in muro and as enzymic products generated in vitro with native extensin monomers as substrates. However, some extensin monomers contain variations within their putative cross-linking motifs that complicate cross-link identification. Other simpler extensins are recalcitrant to isolation including the ubiquitous P3-type extensin whose major repetitive motif, Hyp)(4)-Ser-Hyp-Ser-(Hyp)(4)-Tyr-Tyr-Tyr-Lys, is of particular interest, not least because its Tyr-Tyr-Tyr intramolecular isodityrosine cross-link motifs are also putative candidates for further intermolecular cross-linking to form di-isodityrosine. Therefore, we designed a set of extensin analogs encoding tandem repeats of the P3 motif, including Tyr --> Phe and Lys --> Leu variations. Expression of these P3 analogs in Nicotiana tabacum cells yielded glycoproteins with virtually all Pro residues hydroxylated and subsequently arabinosylated and with likely galactosylated Ser residues. This was consistent with earlier analyses of P3 glycopeptides isolated from cell wall digests and the predictions of the Hyp contiguity hypothesis. The tyrosine-rich P3 analogs also contained isodityrosine, formed in vivo. Significantly, these isodityrosine-containing analogs were further cross-linked in vitro by an extensin peroxidase to form the tetra-tyrosine intermolecular cross-link amino acid di-isodityrosine. This is the first identification of an inter-molecular cross-link amino acid in an extensin module and corroborates earlier suggestions that di-isodityrosine represents one mechanism for cross-linking extensins in muro.     

Uptake of Imidazole and its Effects on the Intracellular pH and Ionic Relations of Chara corallina

Ammonia (pK_a 9.25) and methylamine (pK_a, 10.65) increase cytoplasmicpH and stimulate Cl^– influx in Chara corallina, theseeffects being associated with influx of the amine cations ona specific porter. The weak base imidazole (pK_a 6.96) has similareffects but diffuses passively into the cell both as an unionizedbase and as a cation. When the external pH is greater than 6.0influx of the unionized species predominates. Imidazole accumulates to high concentrations in the vacuole,where it is protonated. Cytoplasmic pH and vacuolar pH riseby only 0.2–0.3 units, suggesting a large balancing protoninflux across the plasma membrane. Balance of electric chargeis partially maintained by net efflux of K⁺ and net influx ofCl^–. Calculation of vacuolar concentrations of imidazole(from (¹⁴C] imidazole uptake, assuming that there is no metabolism)plus K⁺ and Na⁺ indicates an excess of cations over inorganicanions (Cl^–). However, although the osmotic potentialof the cells increases, also indicating increased solute concentrations,the increase is less than that predicted by the calculated ionicconcentrations. This discrepancy remains to be resolved. Becausethe osmotic potential also increases when imidazole is absorbedfrom Cl^–-free solutions it is likely that maintenanceof charge-balance can also involve synthesis and vacuolar storageof organic or amino acids. Key words: Imidazole, potassium, intracellular pH, membrane transport, Chara     

Primary production in lakes Huron and Michigan: in vitro and in situ comparisons

Oxygen- and carbon-14-based primary production estimates from9–16 h in vitro incubations were compared in lakes Huronand Michigan. For surface mixing layer compansons, gross O₂/¹⁴Cphotosynthetic quotients (gross PQ) averaged 2.2, and net O₂/¹⁴Cphotosynthetic quotients (net PQ) averaged 1.4. The mean grossPQ is consistent with a theoretical P0 based on the CO₂ andNO₃ assimilation ratio. However, within the deep chlorophylllayer, gross PQ and net PQ averaged 4.9 and 2.8 respectively.These higher values were likely due to excess NO₃ reductionat the expense of CO₂ uptake. Thus, during short experimentsunder low light conditions, oxygen evolution and CO₂ uptakemay not be tightly coupled. In vitro and in situ O₂ productionestimates were compared in four diurnal (dawn to dusk) experimentsin Lake Huron. In situ production estimates were determinedby measuring water-mass oxygen changes and oxygen transfer acrossthe air-water interface. In situ production estimates were approximatelytwice in vitro production estimates for both surface mixinglayer and deep chlorophyll layer comparisons. The differencebetween estimates was attributable to containment effects manifestin 13–16 h bottle incubations. Short-term (1–2 h)in vitro production was also compared to diurnal in vitro production.Rates of short-term production were {small tilde}1.6 times higherthan rates of diurnal production, suggesting that short-termin vitro production experiments may provide reasonable estimatesof in situ primary production.     

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     

HCO-3 as an Exogenous Carbon Source for Aquatic Bryophytes Fontinalis antipyretica and Fissidens grandifrons

The aquatic bryophytes Fontinalis antipyretica Hedw. and Fissidensgrandifrons Brid. were investigated for their ability to utilizeHCO^–₃ and CO₂ as exogenous carbon sources for photosynthesis.In NaHCO₃ solutions Fontinalis increased the pH to a maximumof 9.6 corresponding to a CO₂ compensation point of 1.1 mmolm^–3 CO₂. Measured photosynthetic rates cannot be explainedonly by uptake of CO₂. Net photosynthesis decreased at highpH but did not decline to zero until pH 10.10 in Fissidens andpH 11.8–12.0 in Fontinalis. Furthermore, photosynthesiswas increased by higher HCO_–3 concentrations at constantCO₂ concentration. It is concluded that Fontinalis antipyreticahas the capability to utilize HCO₃. Key words: Carbon source, Photosynthesis, Aquatic bryophytes     

Photosynthesis and photorespiration in soybean [Glycine max (L.) Merr.] chronically exposed to elevated carbon dioxide and ozone

The effects of elevated carbon dioxide (CO₂ and ozone (O₃) onsoybean (Glycine max (L.) Merr.] photosynthesis and photorespiration-relatedparameters were determined periodically during the growing seasonby measurements of gas exchange, photorespiratory enzyme activitiesand amino acid levels. Plants were treated in open-top fieldchambers from emergence to harvest maturity with seasonal meanconcentrations of either 364 or 726 µmol mol^–1 CO₂in combination with either 19 or 73 nmol mol^–1 O₃ (12h daily averages). On average at growth CO₂ concentrations,net photosynthesis (A) increased 56% and photorespiration decreased36% in terminal mainstem leaves with CO₂ enrichment. Net photosynthesisand photorespiration were suppressed 30% and 41%, respectively,by elevated O₃ during late reproductive growth in the ambientCO₂ treatment, but not in the elevated CO₂ treatment. The ratioof photorespiration to A at growth CO₂ was decreased 61% byelevated CO₂ There was no statistically significant effect ofelevated O₃ on the ratio of photorespiration to A. Activitiesof glycolate oxidase, hydroxypyruvate reductase and catalasewere decreased 10–25% by elevated CO₂ and by 46–66%by elevated O₃ at late reproductive growth. The treatments hadno significant effect on total amino acid or glycine levels,although serine concentration was lower in the elevated CO₂and O₃ treatments at several sampling dates. The inhibitoryeffects of elevated O₃ on photorespiration-related parameterswere generally commensurate with the O₃-induced decline in A.The results suggest that elevated CO₂ could promote productivityboth through increased photoassimilation and suppressed photorespiration. Key words: Photorespiration, CO₂-enrichment, ozone, climate change, air pollution     

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)