Role of alternative pathway respiration in tomato roots attacked by Meloidogyne incognita

The effect of nematode infestation on the alternative pathway respiration of mitochondria isolated from resistant and susceptible tomato roots greatly depended on the oxidisable substrate tested. The percentage of alternative respiration in NADH, malate and succinate oxidation was markedly different between the resistant (Rossol) and the susceptible (Roma VF) cultivars before infestation. Only the percentage of malate alternative oxidation in mitochondria from the resistant roots was influenced by nematode invasion. Conversely, attacked roots showed consistent variations in the content of mitochondria per unit fresh weight and in the phosphorylation efficiency (ADP/O) of the organelles. Expression of the alternative pathway (ρ' value) was found to be unchanged in intact roots and isolated mitochondria six days after nematode inoculation.     

Inheritance of cyanide-resistant respiration in two cultivars of pea (Pisum sativum L.)

Abstract Two pea cultivars (Pisum sativum L., cvs. Alaska and Progress No. 9) shown previously to differ with regard to the appearance of the cyanide-resistant (alternative) pathway of respiration in axis tissue, were found to show this same difference in mature leaf tissue and in epicotyl mitochondria. The possible relationship between dwarf growth form and lack of alternative respiration in cv. Progress No. 9 was tested in two ways. When dwarfism was alleviated in Progress No. 9 by application of exogenous gibberellin A₁, no appearance of the alternative pathway was observed. In a survey of eight other dwarf pea cultivars, five were found to have an alternative pathway comparable to that shown by the tall cv. Alaska, while three lacked the pathway (cf. Progress No. 9). In reciprocal crosses between Alaska and Progress No. 9, the alternative pathway capacity of F₁ progeny resembled that of the maternal parent. This pattern was maintained in all the F₂ generation, indicating maternal inheritance of the trait. These data suggest that alternative respiration in pea is, to some extent, under the control of an organellar genome.     

The Oxidative Phosphorylation and ATPase Activity of Arum spadix Mitochondria in Relation to Heat Generation

The respiration of Arum spadix mitochondria is coupled to asub-maximal stoichiometry of ATP synthesis. The P/O ratios associatedwith the oxidation of succinate or malate are decreased by antimycinand increased by m-chlorobenzhydroxamic acid, an inhibitor ofthe alternative oxidase. The mitochondrial ATPase activity of20–40 nmol (mg protein)^–1 min^–1 is independentof the maturity of the spadix and is unlikely to provide themechanism for heat production during the odoriferous stage,which probably results from an increase in the rate of electrontransport via the non-phosphorylating, cyanide-insensitive oxidase.     

Photosynthesis, Respiration, and Carbon Assimilation in Water-Stressed Maize at Two Oxygen Concentrations

Photosynthesis decreased with decreasing leaf water potentialas a consequence of stomatal closure and possibly non-stimataleffects of severe stress. Assimilation ceased at c. 16x 10⁵Pa. Photo-respiration, in 21% O₂, was small in relation to assimilationin unstressed leaves and decreased as leaf water potential fellbut it was much larger in proportion to photosynthesis at severestress. Decreasing the O₂ content to 1.5% increased photosynthesisslightly and decreased photo-respiration but did not changethe stress at which assimilation stoped. Dark respiration wasinsensitive to both O₂ and stress. Less ¹⁴C accumulated in stressedleaves but in 21% O₂ a greater proportion of it was in aminoacids, particularly glycine and serine. 1.5% O₂ decreased the¹⁴C in glycine to 10% and in serine to 50% of their levels in21% O₂. In both O₂ concentrations the proportion of ¹⁴C in serineincreased only at the most severe stress. Gas exchange measurementsand changes in the ¹⁴C flux to glycine are interpreted as theresult of glycolate pathway metabolism increasing as a proportionof assimilation in stressed leaves in high O₂. The small absoluterate of photorespiration in high O₂ and at low leaf water potentialmay be due to slow rates of glycine decarbodylation as wellas efficient fixation of any CO₂ produced. Serine is synthesizedby an O₂-sensitive pathway and an O₂-insensitive pathway, whichis most active at severe stress. Synthesis of alanine competeswith that of glycine and serine for a common precursor suppliedby the photo-synthetic carbon reduction cycle. The relativespecific radioactivities of aspartate and alanine suggest thatthey are derived from a common precursor pool, probably pyruvatefrom 3-PGA. The amounts of 3-PGA, aspartate, malate, alanine,and sucrose decreased with increasing water stress as a consequenceof slower assimilation and pool filling. Other amino acids,glycine, serine, glutamate, and proline, accumulated at lowwater potential possibly due to increased synthesis and slowerrates of consumption. Changes in pool sizes, carbon fludes,and specific activities of metabolites are related to the mechanismof C₄ photosynthesis and current concepts of glycolate pathwaymetabolism.     

Stimulation of Malate Synthesis by Glycolate in Tomato Leaves in Relation to CO2 Concentration

The mechanism by which malate synthesis from CO2 is increasedunder low concentrations of CO₂ was investigated in C₃ plants.A number of metabolites were administered to illuminated tomatoleaves, and their effects on the incorporation of ¹⁴CO₂ intomalate were determined. Compared with water as a control, glycolate,glyoxylate, D,L-glycerate, glycine, phosphoglycolate and L-serineincreased malate synthesis by factors of 6.8, 3.8, 3.3, 2.5,2.3 and 2.2, respectively. The effect of exogenous glycolateon malate synthesis from CO₂ was dependent on its concentrationup to 100 mu, but was independent of ambient CO₂ concentration.The feeding of l-¹⁴C-glycolate in the light indicated that glycolatestimulated the carbon flow from CO₂ to malate. The analysis of the products of ¹⁴CO₂ fixation in illuminatedleaves supplied with glycolate showed increases in malate andsugar and decreases in serine and phosphate esters. However,this stimulated malate synthesis ceased when malonate was suppliedsimultaneously with glycolate. Treatment with glycolate didnot affect the dark ¹⁴CO₂-fixation, but increased the ¹⁴C-malatesynthesis, with a corresponding decrease in ¹⁴C-aspartate and14^C-glutamate. These results suggest that exogenous glycolateactivates malate dehydrogenase in leaves, and that the increasedglycolate formation at low CO₂ concentrations is associatedwith the increased malate synthesis from CO₂. (Received January 12, 1981; Accepted May 20, 1981)     

PHOTOSYNTHESIS OF GLYCINE AND SERINE IN GREEN PLANTS

1. The effects of "carbonyl" reagents on the photosyntheticin-corporation of ¹⁴CO₂ into the assimilation products of tobaccoand spinach leaves were studied. The presence of "carbonyl"reagents causes an increase in the ratio of ¹⁴CO₂ incorporatedin glycine and a decrease in serine. The incorporation of ¹⁴Cfrom glycolate-1-¹⁴C and glycolaldehyde-2-¹⁴C into glycine andserine was also affected by "carbonyl" reagents, as in the caseof ¹⁴CO₂-experiment. 2. The feeding experiments of glycine-1-¹⁴C and serine-1-¹⁴Cin the presence and in the absence of "carbonyl" reagents revealedthat these reagents inhibit the conversion of glycine to serine. 3. The results obtained above, together with the effects ofthiols on ¹⁴CO₂ incorporation presented in this paper, supportthe assumption that glycine and serine are formed via glycolateand glyoxylate during photosynthesis in green plants. 4. Comparison of ¹⁴C incorporation in malate from ¹⁴CO₂, glycolate-1-¹⁴C,glycine-1-¹⁴C and serine-1-¹⁴C in the presence and in the absenceof "carbonyl" reagents suggested the occurrence of the pathwayof the malate formation via glycolate and glyoxylate, not passingthrough glycine and serine, during photosynthesis. ¹ A part of this paper was presented at the Symposium on "Nitrogenand Plant" by the Japanese Society of Plant Physiologists, inOctober, 1963 ² Present address: Radiation Center of Osaka Prefecture, Sakai,Osaka     

The Effect of Subjecting Peas to Air Enriched with Carbon Dioxide: II. RESPIRATION AND THE METABOLISM OF THE MAJOR ACIDS

Whole peas at about 75 per cent of their maximum fresh weightwere subjected to 5–30 per cent CO₂ in air for periodsof from 1–6 d, then returned to air for a further 1 d.Samples were withdrawn at intervals and organic acids, ^TCO₂and ethanol estimated as well as the rate of respiration. Slicesof cotyledons suspended in water were also subjected to highconcentrations of CO₂ in air for 3 h. The rate of respiration was inhibited progressively by increasein CO₂ content of the tissue. The high internal CO₂ contentof the intact pea causes an inhibition of its rate of respirationby about 25 per cent. Alcohol production commenced at between10 and 15 per cent CO₂ in the ambient gas and slowly increasedin rate up to 37 per cent. The CO₂-air mixtures reduced the content of malate, pyruvateand -oxoglutarate, increased that of succinate and left citrateunaffected. On return to air malate rose rapidly and succinatefell slowly to their original concentrations. During the sameperiod the concentration of PEP fell sharply and after about1 h rose again, whereas oxalacetate showed a reverse response.It is argued that the rapid re-synthesis of malate was by carboxylationof PEP to oxalacetate and that this reaction was stimulatedby a change in pH rather than by the direct effect of the changein concentration of CO₂. In one experiment ¹⁴CO₂ was supplied for 2 h before return toair and the movement of ¹⁴C followed for 6 h. The results supportthe method of re-synthesis of malate proposed.     

Effect of the oxidation of glycine and Krebs cycle substrates on cytochrome activity and alternative pathways of mitochondria from leaves of Pisum sativum L

Isolated mitochondria from adult leaves of Pisum sativum had the capacity to oxidize simultaneously glycine and several substrates of the Krebs cycle (e.g. malate, succinate, citrate, 2-oxo-glutarate), either in the presence of ADP (state three) or in the absence of ADP (state four). The sensitivity of the mitochondrial respiration to inhibitors of the cytochrome (e.g. antimycin A) and the alternative (e.g. salicylhydroxamic acid, SHAM, and tetraethylthiuram disulfide, disulfiram) pathways varied depending on the substrate(s) being used. For instance, the rate of oxygen uptake resistant to antimycin A, which is an estimate of the capacity of the alternative pathway, varied depending on whether glycine was added or not to a medium with malate and succinate. The state four rate of oxygen consumption in the presence of malate or succinate was greatly stimulated by the addition of glycine, and vice versa. This stimulation was apparently mediated by the alternative pathway. The results suggest that part of the electron transport capacity (including the alternative pathway) of these mitochondria is specifically associated with glycine oxidation, and therefore with photo-respiration.     

Oxidations of various substrates and effects of the inhibitors on purified mitochondria isolated from <Emphasis Type="Italic">Kalanchoë pinnata</Emphasis>

Kalanchoë pinnata mitochondria readily oxidized succinate, malate, NADH, and NADPH at high rates and coupling. The highest respiration rates usually were observed in the presence of succinate. The high rate of malate oxidation was observed at pH 6.8 with thiamine pyrophosphate where both malic enzyme (ME) and pyruvate dehydrogenase were activated. In CAM phase III of K. pinnata mitochondria, both ME and malate dehydrogenase (MDH) simultaneously contributed to metabolism of malate. However, ME played a main function: malate was oxidized via ME to produce pyruvate and CO₂ rather than via MDH to produce oxalacetate (OAA). Cooperative oxidation of two or three substrates was accompanied with the dramatic increase in the total respiration rates. Our results showed that the alternative (Alt) pathway was more active in malate oxidation at pH 6.8 with CoA and NAD⁺ where ME operated and was stimulated, indicating that both ME and Alt pathway were related to malate decarboxylation during the light. In K. pinnata mitochondria, NADH and NADPH oxidations were more sensitive with KCN than that with succinate and malate oxidations, suggesting that these oxidations were engaged to cytochrome pathway rather than to Alt pathway and these capacities would be desirable to supply enough energy for cytosol pyruvate orthophosphate dikinase activity.     

Respiratory Loss of Recently Assimilated Carbon in Wheat

A series of experiments was undertaken to assess the amountof respiration associated with the growth of wheat at differentstages. Plants (or in some cases just the flag leaf) were labelledwith ¹⁴CO₂ and the amount of ¹⁴CO₂ respired during the subsequent48 or 72 h was measured. The evolution of ¹⁴C, expressed asa percentage of the amount initially assimilated (referred toas the R/A value) was used as a measure of the overall efficiencyof dry matter production. Respiratory ¹⁴CO₂ evolution from labelledplants was most rapid in the first 12 h after labelling, thereafterdeclining rapidly. Evolution was also more rapid following labellingsat the end of the light period (dusk) than at the beginningof it (dawn). The R/A values were greatest (42 and 50 per centrespectively for dawn- and dusk-labelled plants) for young plantsand least (13 and 28 per cent respectively) for plants duringmid grain filling. When flag leaves, as distinct from wholeplants, were labelled, R/A values were lower still (9 and 21per cent respectively), indicating that flag leaf assimilatewas used efficiently in grain production. The calculated minimum R/A for the formation of grain material(10 per cent protein, 90 per cent starch) was 6.2 per cent.That the experimentally determined values were greater thanthis is attributed to the turnover of carbon in enzymes, toother maintenance processes, and possibly to the operation ofthe pentose phosphate pathway of glucose oxidation. R/A valueswere lower in those plants labelled at the beginning than thoseat the end of the photoperiod. This was considered to be a consequenceof refixation of respiratory ¹⁴CO₂ during the light. The higherR/A values found for young plants were considered to be a consequenceof the greater percentage of ¹⁴C translocated to the roots (rootsbeing unable to refix respired CO₂) and of greater turnoverof enzymes associated with more active metabolism. Triticum, wheat, respiration, carbon assimilation, carbon loss, grain-filling     

Electron Transport and Oxidative Phosphorylation in Arum Spadix Mitochondria

Arum spadix mitochondria exhibited a rapid cyanide-resistantoxygen uptake when oxidizing malate, NADH₂ or succinate, anda slower, cyanide-sensitive oxygen uptake when oxidizing ascorbate+tetramethylphenylenediamine(TMPD). Cytochrome oxidase does not therefore appear to functionas the terminal oxidase in the presence of cyanide, and therather low cytochrome c oxidase activity obtained using ascorbate+TMPDmay exclude it from possessing a major role even in the absenceof cyanide. ATP synthesis has been shown to accompany substrateoxidation. In the presence of antimycin A the P: O ratio accompanyingmalate oxidation was reduced by half, while phosphorylationaccompanying NADH₂ or succinate oxidation was almost completelyabolished. It is proposed that electrons from exogenous NADH₂enter the electron transport chain at a site after that whereendogenous NADH2 donates electrons and that electrons from exogenousNADH₂ are not coupled to ATP synthesis at site 1. The cyanide-resistant,non-phosphorylating electron-transport pathway may functionin the absence of cyanide and account for the low efficiencyof energy conservation observed in this tissue.     

The Inhibition of the Activity of Apple Mitochondria by Oxaloacetate

The inhibitory effect of oxaloacetate (OAA) on the activityof mitochondria isolated from the peel of Cox's Orange Pippinapples has been investigated. A given concentration of OAA causesa longer inhibition of succinate than of malate oxidation andthe rate of disappearance of OAA is faster in the presence ofmalate than in that of succinate. Mg⁺⁺⁺, Al⁺⁺⁺, ATP, and glutamateaccelerate the disappearance of inhibition by OAA; Ca⁺⁺ reinforcesthe inhibition. It is established, by estimation of the oxoacids in the reaction mixtures, that the relief from inhibitionis directly due to removal of OAA. The fall in rate of O₂ uptakewith time, using succinate or malate as substrate, is accompaniedby an accumulation of OAA, and the inhibition of succinate oxidationby malate is due to the increased OAA production when malateis oxidized. Some OAA is broken down non-enzymically to formpyruvate and the rate of breakdown is enhanced by Mg⁺⁺; someis metabolized via the Krebs cycle; some disappear in a coupledreaction between pyruvic and malic dehydrogenases to form citrateand malate, and some can be removed by transamination. It issuggested that all these may be factors in a regulatory actionof OAA on the operation of the Krebs cycle. It is relevant inthis connexion that very small amounts of OAA inhibit the activityof the Krebs cycle when they are produced at the active siteswithin the mitochondrion.     

Tricarboxylic Acid Cycle Activity in Mitochondria from Soybean Nodules and Cotyledons

Infected cells of soybean (Glycine max) nodules require NADH,ATP, and 2-oxoglutarate for ammonia assimilation. The role ofmitochondria in nodule metabolism was investigated by determiningtheir respiratory properties and comparing them with cotyledonmitochondria. Nodule mitochondria oxidized malate at a ratetwice that of any other NAD-linked substrate although theirmalic enzyme activity was very low, accounting for only 12%of malate oxidation at pH 6.4 compared to 56% for cotyledonmitochondria. The reduction of NAD⁺ in mitochondria of noduleson adding malate (determined by fluorescence) was rapid andreached a stable level, whereas in cotyledon mitochondria theNADH level declined rapidly as oxaloacetate accumulated. Anoxaloacetate scavenging system in the mitochondrial reactionmedium increased malate oxidation by cotyledon mitochondria4-fold, but increased that of nodule mitochondria by less than50%. This demonstrates that the efflux of oxaloacetate by theoxaloacetate carrier is highly regulated by the extra-mitochondrialoxaloacetate concentration in cotyledon mitochondria comparedto nodule mitochondria. The activity of TCA cycle enzymes, exceptmalate and succinate dehydrogenases, was low in nodule mitochondria.Their oxaloacetate export during malate oxidation was rapid.The aspartate amino transferase activity associated with nodulemitochondria was sufficient to account for significant formationof 2-oxoglutarate from oxaloacetate and glutamate. These resultssuggest that nodule mitochondria operate a truncated form ofthe TCA cycle and primarily oxidize malate to provide oxaloacetateand ATP for NH₃ assimilation. Key words: Glycine max (L.), nitrogen fixation, gluconeogenesis, respiration     

Stimulation of the Alternative Pathway by Succinate and Malate

Stimulation of the cyanide-resistant oxidation of exogenous NADH in potato (Solanum tuberosum L. cv Bintje) tuber callus mitochondria was obtained with succinate, malate, and pyruvate. Half-maximal stimulation was observed at a succinate or malate concentration of 3 to 4 mM, which is considerably higher than that found for pyruvate (0.128 mM). No effect of succinate or malate addition was found when duroquinone was the electron acceptor. Duroquinol oxidation via the alternative pathway was poor and not stimulated by organic acids. Under stimulating conditions, no swelling or contraction of the mitochondria could be observed. Conversely, variation of the osmolarity did not affect the extent of stimulation. However, the assay temperature had a significant effect: no stimulation occurred at temperatures below 16 to 20[deg]C. Membrane fluidity measurements showed a phase transition at about 17[deg]C. Ubiquinone reduction levels were not significantly higher in the presence of succinate and malate, but the kinetics of the alternative oxidase were changed in a way comparable to that found for stimulation by pyruvate. At low temperatures the alternative oxidase displayed "activated" kinetics, and a role for membrane fluidity in the stimulation of the alternative pathway by carboxylic acids is suggested.     

Malate Decarboxylation by Mitochondria of the Inducible Crassulacean Acid Metabolism Plant Mesembryanthemum crystallinum

Mitochondria isolated from leaves of Mesembryanthemum crystallinumoxidized malate by both NAD malic enzyme and NAD malate dehydrogenase.Rates of malate oxidation were higher in mitochondria from plantsgrown at 400 mil NaCl in the rooting medium and performing Crassulaceanacid metabolism (CAM) than in mitochondria from plants grownat 20 mM NaCl and exhibiting C₃-photosynthetic CO₂ fixation.The mitochondria isolated from plants both in the CAM and C₃modes were tightly coupled and gave high respiratory control.At optimum pH for malate oxidation (pH 7.0), pyruvate was themajor product in mitochondria from CAM-M. crystallinum, whereasmitochondria from C₃-M. crystallinum produced predominantlyoxaloacetate. Both the extracted NAD malic enzyme in the presenceof CoA and the oxidation of malate to pyruvate by the mitochondriafrom plants in the CAM mode had a pH optimum around 7.0 withactivity declining markedly above this pH. The activity of NAD-malicenzyme, expressed on a cytochrome c oxidase activity basis,was much higher in mitochondria from the CAM mode than the C₃mode. The results indicate that mitochondria of this speciesare adapted to decarboxylate malate at high rates during CAM. ¹Current address: Lehrstuhl für Botanik II, UniversitätWurzburg, Mittlerer Dallenbergweg 64, 8700 Würzburg, WestGermany. ²Current address: KD 120, Chemical Research Division, OntarioHydro, 800 Kipling Avenue, Toronto, Ontario M8Z5S4, Canada. ³Current address: Department of Botany, Washington State University,Pullman, Washington 99164-4230, U.S.A. (Received March 13, 1986; Accepted September 18, 1986)     

Biosynthetic mechanism of glycolate in Chromatium I. Glycolate pathway

The pattern of radioactivity distribution in several amino acidsof Chromatium cells exposed to ¹⁴CO₂ was determined. By transferringthe bacterial cells from an atmosphere of nitrogen to oxygenthere occurred a transient decrease of ¹⁴CO₂ incorporation intoaspartate and glutamate, whereas that into glycine showed aprominent increase. The labeling of both serine and alaninedid not show a marked change under such conditions. The, activitiesof glycolate oxidase and glycolate dehydrogenase in crude extractsof the bacterial cells were very low. The formation of glycolic acid only occurred during the oxidativemetabolism of Chromatium cells grown on bicarbonate as a C source,being negligibly small in bacteria under nitrogen or after growthon malate or acetate. The activities of both ribulose- 1,5-bisphosphateoxygenase and phosphoglycolate phosphatase in the extract preparedfrom the bicarbonate-grown bacterial cells were very low andapparently could not account for the glycolic acid formationthrough these enzymic reactions. Metabolic patterns of glycolicacid in Chromatium are discussed in relation to the photorespiratoryphenomenon. (Received February 24, 1975; )     

Cyanide-and rotenone-resistant respiration in mitochondria of sugar beet taproots during plant growth and development

Effects of cyanide and rotenone were examined on respiration (oxygen uptake) in mitochondria isolated from sugar beet (Beta vulgaris L.) taproots at various stages of plant growth and development. In mitochondria from growing and cool-stored taproots, the ability of cyanide-resistant, salicylhydroxamic acid-sensitive alternative oxidase (AO) to oxidize malate, succinate, and other substrates of tricarboxylic acid cycle (TCA) was low and constituted less than 10% compared to predominant activity of the cytochrome oxidase pathway during State 3 respiration. Artificial aging of storage tissue (2-day incubation of tissue sections under high humidity at 20°C) substantially activated AO, but the highest capacity (V _alt) of this pathway of mitochondrial oxidation was only observed in the presence of pyruvate and a reducing agent dithiothreitol. At the same time, mitochondria from growing taproots exhibited high rates of rotenone-resistant respiration, and these rates gradually declined during plant growth and development. The slowest rates of this respiration were observed during oxidation of NAD-dependent TCA substrates in mitochondria from dormant storage organ. The results are discussed in relation to significance of alternative electron transport pathways during growth and storage of sugar beet taproots.     

Glycine as a substrate for photorespiration

Substrates for photorespiration were examined by feeding ¹⁴Clabeled compounds to tobacco and corn leaf segments and by measuring¹⁴CO₂ evolution in light and darkness. CO₂ release in the darkwas rapid, but in light CO₂ release was slow due to refixationby photosynthesis. Carboxyl labeled glycine was more rapidlydecarboxylated than were glyoxylate, glycolate or serine. Hydroxypyridinemethanesulfonate, an inhibitor of glycolate oxidase, blocked CO₂ releasefrom glycolate but not from glycine. Isonicotynyl hydrazideblocked CO₂ release from both glycine and glycolate. DCMU blockedphotosynthetic refixation of the released CO₂, consequentlythe rates of CO₂ release in light and dark were about equal.It was concluded that CO₂ release during photo-respiration camefrom the conversion of 2 molecules of glycine to one serineand one CO₂. ¹⁴CO₂ release from glycine-l-¹⁴C in the dark or with DCMU inlight can be used as an assay for photorespiration ability. CO₂ release from glycine and glycolate by corn leaf segmentsin the dark proceeded at the rate of that in normal tobaccoleaf. This result, together with other work on O₂ exchange andenzymatic analysis, indicates that corn and other plants docarry on photorespiration, but it is not manifested by CO₂ releasein light. A yellow tobacco mutant, Consolation 402, had high rates ofphotorespiration by the ¹⁴CO₂ assay, nearly half (or more) asmany peroxisomes as chloroplasts, and high rates of CO₂ releasefrom glycine-l-¹⁴C or glycolate-l-¹⁴C. A common tobacco, BrightYellow, had lower rates of photorespiration, fewer visible peroxisomes,and slower decarboxylation of glycine and glycolate. The amount of ¹⁴CO₂ release from glycine-l-¹⁴C or glycolate-l-¹⁴Cincreased only slightly when the temperature was raised from25 to 35°C. ¹Parts of this work were abstracted at the Annual Meeting (April,1969) of Japanese Society of Plant Physiologists, Kanazawa ²Department of Biochemistry, Michigan State University, EastLansing, Michigan, U.S.A. (Received September 3, 1969; )     

The Transport of Photosynthetic Products from the Chloroplasts of Tobacco Leaves

Tobacco leaves were fractionated by the non-aqueous method afterphotesynthesis for short periods in ¹⁴CO₂ and with or withoutsubsequent photosynthesis in ¹²CO₂ or respiration in the dark.Phosphate esters became labelled only slowly in the non-chloroplastparts of the leaf; glycine and serine which became rapidly labelledin the non-chloroplast leaf fraction appear to be concernedin the transport of newly assimilated carbon from the chloroplast.     

Biosynthetic mechanism of glycolate in Chromatium IV. Glycolate-glycine transformation

The metabolic transformation of glycolate to glycine occurringin photosynthesizing cells of Chromatium was investigated bythe radioisotopic technique and by amino acid analysis. By analyzingthe distribution of radiocarbon upon feeding [1-¹⁴C] glycolate,[2-¹⁴C] glyoxylate and [1-¹⁴C] glycine to bacterial cells, itwas demonstrated that glycolate is converted to glycinc viaglyoxylate, and both glycolate and glycine are excreted extracellularly.Although the formation of serine was barely detected by theabove two techniques in both N₂ and O₂ atmospheres, it was foundthat ¹⁴CO₂ is evolved quite markedly from both [1-¹⁴C] glycolateand [1-¹⁴C] glycine fed to the Chromatium cells. Analyticalresults of transient changes in amino acid compositions underatmospheric changes of N₂O₂ and by the addition of exogenousglycolate in N₂ confirm the notion that glycolate is convertedto glycine. Acidic amino acids (glutamic acid and aspartic acid)appear to take part in glycine formation as amino donors. Theformation of glycine from glycolate in a N₂ atmosphere suggeststhat an unknown glycolate dehydrogenation reaction may operatein the overall process. ¹ This is paper XXXVII in the series ‘Structure and Functionof Chloroplast Proteins’. Paper XXXVI is ref. (5). Theresearch was supported in part by grants from the Ministry ofEducation of Japan (No. 111912), the Toray Science Foundation(Tokyo) and the Naito Science Foundation (Tokyo). (Received July 14, 1976; )