Studies on the Growth in Culture of Plant Cells: XV. UPTAKE AND UTILIZATION OF URIDINE DURING THE GROWTH OF ACER PSEUDOPLATANUS L. CELLS IN SUSPENSION CULTURE

[2-¹⁴C]-uridine is rapidly taken up by sycamore cells in suspensionculture. A proportion of the radioactivity enters RNA withoutmeasurable delay, whilst the remainder equilibrates with a largepool of phosphorylated compounds, the major radioactive componentof which is 5'-UMP. Both the uracil and cytosine residues ofRNA receive label from [¹⁴C]-uridine and, when the cells aresupplied with high concentrations of uridine, these bases arederived almost exclusively from the nucleoside. [¹⁴C]-uridine is incorporated into RNA at all stages of thegrowth cycle of batch cultures; its continuing incorporation,when the total RNA content of the cells is rapidly decreasing,indicates a high rate of turnover of the total RNA. Long-termlabelling experiments also indicate turnover of RNA during thephase of active cell division and suggest that a large proportionof the degradation products are not re-utilized for RNA synthesis. Sycamore cells degrade [2-¹⁴C]-uridine with release of ¹⁴CO₂.The proportion degraded increases from 25 per cent at an externaluridine concentration of 10^–6M to 75 per cent at 10^–3M. Despite this, nucleic acids are the only macromolecules thatreceive a significant amount of radioactivity from [2-¹⁴]C-uridine.     

Glucose and Pyruvate Metabolism in Daucus carota Cells: The Effect of the Ammonium Ion

In Daucus carota cells cultivated in vitro, the ammonium ionstimulates the incorporation of radioactivity from labelledglucose and labelled pyruvate into CO₂ and into the residueinsoluble in 60 per cent (v/v) ethanol. There is a higher ¹⁴CO₂production from [6-¹⁴C₂] glucose than from [6-¹⁴C] glucose.These results suggest a possible stimulation of glycolysis bythe ammonium ion.     

Metabolism of Glycollate by Lemna minor L. Grown on Nitrate or Ammonium as Nitrogen Source

Marques, I. A., Oberholzer, M. J. and Erismann, K. H. 1985.Metabolism of glycollate by Lemna minor L. grown on nitrateor ammonium as nitrogen source.—J. exp. Bot. 36: 1685–1697. Duckweed, Lemna minor L., grown on inorganic nutrient solutionscontaining either NH₄⁺ or NO₃^– as nitrogen source wasallowed to assimilate [1-¹⁴C]- or [2-¹⁴C]glycollate during a20 min period in darkness or in light. The incorporation ofradioactivity into water-soluble metabolites, the insolublefraction, and into the CO₂ released was measured. In additionthe extractable activity of phosphoenolpyruvate carboxylasewas determined. During the metabolism of [2-¹⁴C]glycollate in darkness, as wellas in the light, NH₄⁺ grown plants evolved more ¹⁴CO₂ than NO₃^–grown plants. Formate was labelled only from [2-¹⁴C]glycollateand in NH₄⁺ grown plants it was significantly less labelledin light than in darkness. In NO₃^– grown plants formateshowed similar radioactivity after dark and light labelling.The radioactivity in glycine was little influenced by the nitrogensource. Amounts of radioactivity in serine implied that thefurther metabolism of serine was reduced in darkness comparedwith its metabolism in the light under both nitrogen regimes.In illuminated NH₄⁺ plants, serine was labelled through a pathwaystarting from phosphoglycerate. After [1-¹⁴C]glycollate feedingNH₄⁺ grown plants contained markedly more radioactive aspartateand malate than NO₃^– plants indicating a stimulated phosphoenolpyruvatecarboxylation in plants grown on NH₄⁺. Key words: Photorespiration, glycollate, nitrogen, Lemna     

Proline-14C metabolism in barley seedlings during vernalization

The metabolism of proline-¹⁴C was examined in vernalized (LT)and unvernalized (HT) barley shoots. The content of prolinein cytoplasmic and cell wall protein fractions was a littlehigher in HT, against the accumulation of free proline in LT.Proline-¹⁴C was more heavily incorporated into HT and the cytoplasmicprotein had a higher radioactivity than the cell wall protein.In LT, the activity in the cytoplasmic protein was lower thanthat in the cell wall. The time course of incorporated proline-¹⁴Cshowed no distinct changes in HT. but decreased remarkably inthe LT cell wall. The distribution of proline-¹⁴C in hydroxyproline and otheramino acids in the two proteins was examined. In the cytoplasmicproteins, the conversion pattern of proline-¹⁴C was very similarin both treatments. The highest hydroxyproline activity wasfound at the beginning of incubation and was maintained at acomparatively high level in the HT cell wall. The LT cell wallshowed a gradual increase in radioactivity due to hydroxyprolineand reached maximum conversion at the last incubation period.Distribution of radioactivity due to incorporated proline-¹⁴Cwas examined by separating barley shoot tissues into three sections. (Received December 5, 1972; )     

Distribution of Radioactivity from Exogenously Supplied [1-14C]Indol-3-yl-acetic Acid and [3, 4-3H (N)] Gibberellin A, in Geotropically-stimulated Picea abies (L.) Karst. Roots

The distribution of exogenously-supplied radioactive labelledindol-3-yl-acetic acid (IAA) and gibberellin A₁ (GA₁) in geotropicallystimulated roots of Norway spruce (Picea abies (L.) Karst.)has been demonstrated. Seedlings were positioned with theirroot tips in 2.1 x 10^–6 M [¹⁴C]IAA or 1.3 x 10^–8m ³H-GA₁ for 4 and 20 h, respectively. After geotropic stimulationfor 90 min in the horizontal position the root tips were cutlongitudinally in 50 µm thick sections, using a freeze-microtome.The radioactivity in the ¹⁴C-IAA treated roots occurred in higherconcentration in the lower than in the upper halves (ratio 1.25:1). A similar trend was observed in the [³H]GA₁-treated rootswhere the ratio lower: upper halves was 2.04: 1. The ratio ofradioactivity in right and left halves of vertical roots wasapproximately the same in roots supplied with [¹⁴C]IAA and [³H]GA₁(1.09: 1). The supplied radioactive compounds were analysed chromatographicallyafter extraction in methanol of 6 mm apical root segments. Onlya small fraction (7–8 per cent) of the supplied [¹⁴C]IAAwas revealed unchanged in the segments. The major part of thechromatographed, labelled compound has not been identified,but on basis of its R_F value it is suggested that it may beindol-3-acetyl-aspartic acid (IAAasp). The chromatographic analysis of the [³H]GA,-treated segmentsshowed that only small fractions of this gibberellin has beenconverted to other compounds. These results have been discussed and correlated with knowledgeof plant growth regulators and their participation in root geotropism. Picea abies, spruce, geotropism, gibberellin A₁, indol-3-yl-acetic acid, growth regulators, redistribution in roots     

Fruit Softening II. Precursor Incorporation into Pectin by Pear Tissue 6

The incorporation of radioactivity from precursors of methylester and galacturonosyl residues into pectin was investigatedusing tissue slices cut from ripening pear fruits. Incorporationfrom ¹⁴CH₃ methionine into methyl ester of water soluble pectinincreased 10 fold in 4 d at 18 °C and declined in laterstages of ripening. Activity from [³H]inositol could not bedetected in gaJacturonic acid released enzymically from solublepolysaccharides. When l³H]glucose was used as a precursor, activitycould be detected in galacturonic acid released from both thesoluble and insoluble polysaccharide fractions. Methionine wasa more efficient precursor of methyl ester groups than S-adenosylmethionine or S-methyl methionine; incorporation from all threeprecursors was inhibited under nitrogen. Radioactively labelledmethyl ester did not decline during a 225 min ‘chase’following a 15 min ‘pulse’ of [¹⁴CH₃]methionine;the total pectin content of slices increased by 20% during this4 h incubation.     

Biosynthesis of Caffeine in Flower Buds of Camellia sinensis

The biosynthesis of purine alkaloids in flower buds of tea plantswas investigated. More than 25% of total radioactivity of [8-¹⁴C]adeninetaken up by stamens isolated from tea flower buds was foundto have been incorporated into purine alkaloids, namely, theobromineand caffeine, 24 h after administration of the labelled compound.Pulse-chase experiments indicated that [8-¹⁴C]adenine takenup by the stamens was converted to adenine nucleotides and subsequentlyincorporated into theobromine and caffeine. Since 5 µMcoformycin, an inhibitor of AMP deaminase, inhibited the incorporationof radioactivity into the purine alkaloids, synthesis of caffeinefrom adenine nucleotides seems to be initiated by the reactionof AMP deaminase. Although most of the radioactivity from [8-¹⁴C]inosinewas recovered as CO₂ and ureides, considerable amounts of radioactivitywere recovered as purine alkaloids. The incorporation of radioactivityfrom [8-¹⁴C]inosine into the purine alkaloids was not affectedby coformycin. The five enzymes involved in synthesis of 5-phosphoribosyl-1-pyrophosphatefrom glucose were present in the stamens and petals of tea flowerbuds. From present and previous results, the pathway for thebiosynthesis of caffeine from adenine nucleotides in flowerbuds of tea is discussed.Copyright 1993, 1999 Academic Press Camellia sinensis, tea, stamen, flower, biosynthesis, purine alkaloids, caffeine, theobromine, adenine nucleotides, nucleotide biosynthesis     

Evidence for Several Galactan Synthases in Flax (Linum usitassimum L.) Suspension-Cultured Cells

A membrane fraction from flax cells was able to incorporate[¹⁴C]galactose from UDP-D-[¹⁴C]galactose in vitro. The productsof the reaction, characterized by methylation analysis, consistedof a rß-1,4-galactan (solubilized mainly in water)and a rß-1,3- rß-1,6-galactan (solubilizedmainly in alkali). These results indicated the presence of severalgalactan synthase complexes, as did a profile of the relationshipbetween pH and activity which revealed both a maximum at pH6.5 and a shoulder at pH 8. Moreover, galactan synthase activitieswere found at two densities: 1.125 g cm^–3 (Golgi membranes)and 1.07–1.08 g cm^–3 (corresponding to low-densityvesicles). Partial characterization of one enzymatic system (maximaly activeat pH 8 in the presence of 5 mM MgCl₂) was achieved. The K_mfor UDP-galactose and V_max were 38 µM and 4.5 nmol h^–1(mg protein)^–1, respectively. (Received June 6, 1993; Accepted September 22, 1993)     

Azetidine-2-carboxylic Acid and Lily Pollen Tube Elongation

Azetidine-2-carboxylic acid (AZC), which occurs naturally inLiliaceous plants, is reported to be a proline (pro) analoguePlant cell walls contain ‘extensin’, which is richin hydroxyproline (hyp). Peptidyl hyp arises through hydroxylationof peptidyl pro followed by glycosylation (arabinose attachment)of hyp Because AZC replaces peptidyl prolyl residues, it maybe a useful tool for evaluating the significance of hyp-o-arabinoselinkages in cell elongation. Therefore, we determined the effectof AZC on [¹⁴C]pro uptake, incorporation and conversion to wall-bound[¹⁴C]hyp in relation to elongation of lily pollen tubes whosewalls consist, in part, of hyp-containing glycopeptides TheAZC suppressed pollen germination 9–42 per cent (1–10mM) and subsequent tube elongation 40–54 per cent (0·1–1mM without affecting respiration In contrast, similar hyp concentrationswere without effect on tube elongation Whereas uptake of [¹⁴C]prowas 16·5–6·2 per cent of the control at0·1–1 mM AZC, [¹⁴C]leucine uptake was 85–25per cent of the control. Light microscope radioautography revealedfewer silver grains over tubes elongated in 0·1–1mM AZC than in its absence. Incorporation of [¹⁴C]pro into tnchloroaceticacid (TCA)-precipitable cytoplasm was reduced by only 10 percent at 0·01–1 mM but 43 per cent at 10 mM AZCGel filtration of cytoplasm from pollen germinated without AZCbut with [¹⁴C]pro resulted in labelled void volume (V) and threeretarded peaks (RI–III) Incorporation into V and RI wasinhibited at both 0·01 and 1 mM AZC These AZC concentrationsreduced conversion of [¹⁴C]pro to wall-bound hyp by 20 percent However, total incorporation of [¹⁴C]pro into salt-water-purifiedwall fractions was suppressed 47–53 per cent (0·1–1mM AZC). Lilium longiflorum, lily, hydroxyproline, proline, azetidine-2-carboxylic acid, pollen, pollen tube elongation     

Rhamnogalacturonan-II--a biologically active fragment

Rhamnogalacturonan-II inhibited the uptake of [¹⁴C]leucine and,consequently, the incorporation of [¹⁴C]leucine into acid-precipitableproteins by suspension-cultured tomato cells. Fractionationof rhamnogalacturonan-II showed that the lower molecular componentswere the most effective. KDO and apiose, both constituents ofrhamnogalacturonan-II, also inhibited [¹⁴C]leucine incorporationweakly, suggesting that these sugar residues may be an integralrequirement for the biological activity of rhamnogalacturonan-II.The incorporation of [¹⁴C]glutamate and [¹⁴C]histidine, andto a lesser extent [¹⁴C]proline and [¹⁴C]arginine, was alsoinhibited by rhamnogalacturonan-II; the incorporation of [¹⁴C]tyrosineand [¹⁴C]phenylalanine was little affected. This suggests thatrhamnogalacturonan-II exerts its effect by acting on certainmembrane transport systems. Key words: Rhamnogalacturonan-II, inhibition, protein synthesis, amino acid incorporation     

Tunicamycin inhibits protein glycosylation in suspension cultured soybean cells

Soybean cells in suspension culture incorporate [³H]mannose into dolichyl-phosphoryl-mannose and into lipid-linked oligosaccharides as well as into extracellular and cell wall macromolecules. Tunicamycin completely inhibited the formation of lipid-linked oligosaccharides at a concentration of 5 to 10 micrograms per milliliter, but it had no effect on the formation of dolichyl-phosphoryl-mannose. Tunicamycin did inhibit the incorporation of [³H]mannose into cell wall components and extracellular macromolecules, but even at 20 micrograms per milliliter of antibiotic there was still about 30% incorporation of mannose. The radioactivity in these macromolecules was localized in mannose (70%), rhamnose (20%), galactose (8%), and fucose (2%) in the absence of antibiotic. But when tunicamycin was added, very little radioactive mannose was found in cell wall or extracellular components. The incorporation of [³H]leucine into membrane components and [¹⁴C]proline into cell wall components by these suspension cultures was unaffected by tunicamycin. However, tunicamycin did inhibit the appearance of leucine-labeled extracellular macromolecules, probably because it prevented their secretion.     

Long chain fatty acid synthesis in developing castor bean seeds IV. The synthetic system in proplastids

The proplastid fraction containing no cytosol and mitochondrionwas isolated from developing castor bean endosperm by stepwisesucrose density centrifugation. This fraction possesses thecapacity to synthesize LFAs from [u-14C]sucrose, [u-¹⁴C]-glucose,[u-¹⁴C]G-1-P, [u-¹⁴C]G-6-P, [2-¹⁴C]pyruvate and [1-¹⁴C]acetate.Little was incorporated from [1-¹⁴C]pyruvate into LFAs, butmuch into ¹⁴CO_a. Addition of cytosol to the proplastid fractiondid not enhance the LFA synthesis. From these data, the wholepath from sucrose to LFAs through glycolytic path and pyruvatedecarboxylation seems to be located within the proplastid indeveloping castor bean endosperm. The difference in utilizationof substrates indicates that the rate of LFA synthesis in castorbean proplastids is limited at a step between sucrose and hexosephosphate. In addition, experiments with CO₂ output and LFAsynthesis from [1-¹⁴C]glucose, [6-¹⁴C]glucose and [u-¹⁴C]G-6-Pstrongly suggest that the path flow branches actively throughG-6-P to the pentose phosphate path and little through acetylCoAto the TCA cycle. (Received May 12, 1975; )     

H(+)-linked transport of salicylic acid, an NSAID, in the human trophoblast cell line BeWo

We investigated thetransport of salicylic acid and L-lactic acid across theplacenta using the human trophoblast cell line BeWo. We performeduptake experiments and measured the change in intracellular pH(pH_i). The uptakes of [¹⁴C]salicylic acid andL-[¹⁴C]lactic acid were temperature- andextracellular pH-dependent and saturable at higher concentrations. Bothuptakes were also reduced by FCCP, nigericin, and NaN₃.Various nonsteroidal anti-inflammatory drugs (NSAIDs) stronglyinhibited the uptake of L-[¹⁴C]lactic acid.Salicylic acid and ibuprofen noncompetitively inhibited the uptake ofL-[¹⁴C]lactic acid.-Cyano-4-hydroxycinnamate (CHC), a monocarboxylate transporterinhibitor, suppressed the uptake ofL-[¹⁴C]lactic acid but not that of[¹⁴C]salicylic acid. CHC also suppressed the decrease ofpH_i induced by L-lactic acid but had littleeffect on that induced by salicylic acid or diclofenac. These resultssuggest that NSAIDs are potent inhibitors of lactate transporters,although they are transported mainly by a transport system distinctfrom that for L-lactic acid.

     

Growth of Ryegrass (Lolium perenne L.) Exposed to SO2: II. CHANGES IN THE DISTRIBUTION OF PHOTO ASSIMILATED 14C

Perennial ryegrass (Lolium perenne L.) cv. S23 was exposed to0, 50, and400 µg m– ³ SO₂ for a 29 d period, harvested,and then exposed under the same regime for a further 22 d periodof regrowth. Leaves from plants representing each exposure concentrationwere photosynthetically fed ¹⁴CO₂ for 5 min at the end of eachperiod. A significant increase in photoassimilation of ¹⁴CO₂and retention of ^I4C, concomitant with significant decreasesin [¹⁴C]glycine and [¹⁴C]serine with increasing SO₂ concentration,implied that there was an inhibition of the photorespiratorypathway. At the second harvest, leaves from plants exposed to400 µg m– ³ SO₂ also exhibited significant increasesin [¹⁴C]sucrose and [¹⁴C]fructose.     

The metabolism of proline in cotyledons of pumpkin (Cucurbita moschata)

Exogenous proline-U-₁₄C is readily metabolized to glutamate,ornithine, sugars, CO₂, and organic acids, and is incorporatedinto protein by etiolated and green pumpkin cotyledons. As littletranslocation of proline from the cotyledons occur, it was proposedthat in young tissue proline is converted to glutamate, ornithineor sugar which are then readily translocated from the cotyledons.In older tissue some glutamate carbon derived from proline isalso used as an energy source and metabolized to CO₂. As proteinsynthesis is occurring rapidly in these cotyledons, considerableproline is incorporated into new protein. After 10-hr, 15% ofthe absorbed radioactivity still remained as free proline. ¹Present address: Instituto de Ciencias Biologicas, UniversidadeFederal de Vicosa, Vicosa, Minas Gerais, Brasil. (Received February 1, 1974; )     

The Effects of Leaf Age and Senescence on the Distribution of Carbon in Lolium temulentum

Assimilate distribution in leaves of Lolium temulentum was establishedby root absorption of [¹⁴C]sucrose and after exposure to ¹⁴CO₂.Age determined the amount of carbon assimilated, with more labelbeing incorporated during expansion than at maturity. Duringsenescence ¹⁴C assimilation was much lower. Ethanol-solubleextracts from various tissues of root-labelled plants containedmost of the radioactivity chiefly in basic and acidic compounds.The neutral fraction was composed predominantly of sucrose. Sucrose was comparably labelled in leaves from plants fed equalamounts of either [¹⁴C]sucrose, glucose, or fructose and onlytraces of labelled monosaccharides appeared in extracts. Radioactive sucrose was translocated rapidly from mature leaveswhereas, in the expanding leaf, carbon incorporation was directedtowards growth and the greater proportion of label present atligule formation was in ethanol-insoluble material. Induced senescence, of a mature leaf fed during expansion, produceda rapid loss from the pool of insoluble ¹⁴C. This was accompaniedby a reduction in the contents of chlorophyll and soluble proteinand an accumulation of amino acids. The onset of senescencecaused changes in leaf sugar levels which were correlated withincreased rates of respiration.     

Trimming and solubilization of xyloglucan after deposition in the walls of cultured rose cells

A pulse-chase technique involving the in vivo feeding of L-[1-³H]arabinoseto suspension-cultured rose (Rosa) cells at 4 d and 9 d aftersubculture (fast- and slow-growing, respectively) was used tocreate a population of [³H]xyloglucan molecules and to followtheir subsequent fate. The weight-average relative molecu larmass (M_w) of [³H]xyloglucan freshly deposited in the cell wallwas 160 000 and 240 000 in the fast- and slow-growing cells,respectively. The wall-bound [³H]xyloglucan of both culturesunderwent a decrease in M_w of 40 000 during the first 2 d afterthe pulse-labelling. At the same time, 20–30% of the initially-deposited[³H]xyloglucan disappeared from the cell wall, and a similaramount appeared in solution in the culture medium. Its failureto remain bound to the cell wall and its low M_w (39 000) indicatedthat this soluble extracellular ( was derived from partial degradationof segments of wall-bound xyloglucan that were not directlyhydrogen-bonded to microfibrils (‘loose ends’ and‘tethers’). The possible enzymic basis and biologicalroles of the degradation are discussed. Key words: Cell expansion, cell wall, hemicellulose, sloughing, xyloglucan     

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; )     

Effects of Certain Inhibitors on Photorespiration by Wheat Leaf Segments

The effect on the carbon metabolism of wheat leaf segments ofcertain inhibitors of photorespiration was studied. Sodium 2-hydroxy-3-butynoatesupplied for 40 min resulted in accumulation of ¹⁴C in glycolicacid with only a 7% inhibition of photosynthesis; when suppliedfor 90 min, photosynthesis was inhibited by 47%. When ¹⁴CO₂was replaced by 1000 vpm ¹²CO₂, radioactivity in glycine decreasedbut increased more rapidly in sucrose with less release of ¹⁴CO₂.Isonicotinyl hydrazide (INH) inhibited photosynthesis from ¹⁴CO₂by 50% and glycine replaced sucrose as the main product. When,after 15 min, ¹⁴CO₂ was replaced by 150 vpm ¹²CO₂, in the presenceof INH less ¹⁴CO₂ was released, ¹⁴CO in glycine decreased moreslowly, and less [¹⁴CO]sucrose accumulated. Glycidate (potassium2,3-epoxypropionate) at 2 mM had no effect on photosyntheticrate and little effect on carbon metabolism; 20 mM glycidateinhibited photosynthesis by 64% and resulted in less radioactivityin glycine, more in phosphate esters, and less ¹⁴CO₂ released.When photosynthesis was measured in 1000 vpm CO₂ the inhibitorsgave smaller effects on metabolism than during photosynthesisfrom 150 vpm ¹⁴CO₂ but 20 mM glycidate still resulted in a 42%inhibition of photosynthesis. When U- [¹⁴CO]glycerate was appliedto leaf segments in air with 320 vpm ¹⁴CO₂ the total uptakeof glycerate was not changed by the inhibitors. INH and glycidateboth decreased the amount of glycerate metabolised. More ¹⁴COaccumulated in glycine in the presence of INH and in phosphateesters and serine in the presence of glycidate. Hydroxybutynoateincreased the production of glycolate from glycerate but didnot affect the total amount of glycerate metabolised. Although all three inhibitors affected photorespiratory metabolismnone stimulated photosynthesis. The results are consistent withthe main release of CO₂ in photorespiration arising from theconversion of glycine to serine.     

Involvement of cellulose synthesis in actions of gibberellin and kinetin on cell expansion. Gibberellin-coumarin and kinetin-coumarin interactions on stem elongation

In azuki bean (Azukia angularis = Vignia angularis) epicotylsections, 5 ? 10^–4 M coumarin inhibited the incorporationof radioactivity from [U^–14C]glucose into the cellulosefraction by 35% in the absence of indole-3-acetic acid (IAA)and by 40% in the presence of 1 ? 10^–4 M IAA. There wasno inhibitory effect on the incorporation of radioactivity intothe other fractions. Coumarin at 5 ? 10^–4 M reversed thepromoting effect of 1 ? 10^–5 M gibberellin A₃ (GA) andthe inhibitory effect of 1 ? 10^–5 M kinetin on IAA-inducedelongation of sections with no significant effects on IAA-inducedelongation. Neither GA nor kinetin had any appreciable effectson cellulose synthesis. No inhibition of cellulose syntheiswas observed with 1 ? 10^–3 M colchichine, which has beenreported to have effects similar to those of coumarin on GA-or kinetin-affected stem elongation. Coumarin at 5 ? 10^–4M was ineffectual in breaking up wall microtubules, while adisrupting effect on wall microtubules was clearly demonstratedwith 3 ? 10^–4M colchicine. From these results, the possible involvement of cellulose synthesisin cell expansion controlled by GA or kinetin was suggested. (Received August 3, 1973; )