Metabolic patterns of 14C incorporation by selected vascular plants following field incubations with acetate-2-14G in two plant successional stages in Glacier Bay, Alaska

Metabolic patterns of some vascular plants (Dryas sp., Vacciniumsp., Salix sp., Alnus sp., Epilobium sp.), occurring in successionalhabitats, following acetate-2-¹⁴C incubations in the field weredemonstrated for the first time. Relative radioactivity withinthe alcoholic soluble fraction of each species reflects itsdistribution in successional communities. A high level of ¹⁴C-sugarswas present in the plants of the pioneer community; on the otherhand a high level of ¹⁴C-organic acids was present in the plantsof the forest community. Three patterns, based on the relativeactivities of the sugar- and organic acid-pools were noted whichcorrespond to the range and the frequency of occurrence of eachspecies in the successional stages. Only two types of ¹⁴C-aminoacid levels were noted corresponding to the range of distribution.Plants having less than 10% relative radioactivity in aminoacid-pools had a limited range of distribution and reside inonly one habitat; plants having more than 10% radioactivityshowed wider ranges of distribution occurring in at least twohabitats. ¹ Contribution 292 of the Institute of Polar Studies, The OhioState University, Columbus, Ohio 43210. (Received April 16, 1975; )     

Ethylene-Enhanced Transport of 14C-Labeled Metabolites in Rice Seedlings in Relation to Ethylene-Stimulated Coleoptile Growth

To examine the effects of ethylene on sugar transport from endospermsto coleoptiles in rice (Oryza sativa L. cv. Sasanishiki) seedlings,the contents of free sugars in the coleoptiles of explants fedcold glucose and the distributions of ¹⁴C-activities after feedingof ¹⁴C-glucose to the scutella were determined at various timesafter ethylene application. Changes in sucrose, glucose andfructose in the cold glucose-fed explants exposed to ethylenewere similar to those in the ethylene-treated intact seedlingshaving endosperms. Ethylene enhanced the transport of ¹⁴C-labeledmetabolites from the scutella to the coleoptiles. Most of the¹⁴C accumulated in the ethylene-treated coleoptiles were presentas neutral substances in the ethanol-soluble fraction. Regardlessof the presence or absence of ethylene, the incorporation of¹⁴C into sucrose preceded that into glucose and fructose. Theglucose and fructose moieties of ¹⁴C-sucrose in the coleoptileswere almost equally labeled, and the specific activities of¹⁴C-sucrose were higher than those of ¹⁴C-glucose and ¹⁴C-fructose.These results suggested that sucrose synthesized in the scutellawas exported to the coleoptiles, and cleaved there into glucoseand fructose. Ethylene may accelerate the transport of ¹⁴C-labeledmetabolites by activating sucrose cleavage in the coleoptiles. (Received July 1, 1985; Accepted September 17, 1985)     

Action Mechanism of Ethylene in the Control of Sugar Translocation in Relation to Rice Coleoptile Growth I. Sucrose Metabolism

The fate of ¹⁴C-glucose fed through scutella of rice (Oryzasativa L. cv. Sasanishiki) seedling explants was investigatedin relation to ethylene action on sugar translocation to growingcoleoptiles and leaves. In the scutellum, sucrose, UDPglucoseand F6P were rapidly labeled, and sucrose-phosphate synthaseactivity was higher than sucrose synthase activity. Radioactivesucrose soon appeared in both coleoptiles and leaves, and increasedrapidly. Its specific activity in both tissues became almostequal to that in the scutella. The specific activities of ¹⁴C-glucosein both coleoptiles and leaves changed almost in parallel tothose of ¹⁴C-fructose. These results suggest that sucrose wassynthesized in the scutellum and exported to the coleoptileand leaf, where it was cleaved to glucose and fructose. Ethylene slightly increased the specific activities of ¹⁴C-sucrosein all tissues, but markedly increased those of ^l4C-glucoseand -fructose only in the coleoptile. We assume that the ethyleneenhancement of sucrose transport from scutellum to the coleoptileresults from the activation of sucrose unloading in the growingcoleoptile where imported sucrose is cleaved into glucose andfructose. (Received May 25, 1987; Accepted October 30, 1987)     

FORMATION OF LIGNIN IN TISSUE CULTURE OF PINUS STROBUS

The formation of shikimic acid and lignin from glucose in thecambium tissue was investigated. Glucose-1-¹⁴C, shikimic acid-G-¹⁴C, sodium acetate-1-¹⁴C and sodium acetate-2-¹⁴C were administeredto the tissue culture of strob pine. Glucose was well incorporatedinto shikimic acid, but acetic acid was less effective. Shikimicacid was very efficient as a precursor of aromatic nucleus andglucose was also converted efficiently to lignin. The extentof incorporation of acetic acid, however, was considerably low.A possibility was discussed that in the cultured tissue ligninand its precursor were synthesized from glucose via the shikimicacid pathway. (Received May 14, 1960; )     

Characteristics of Nectar Secretion by the Extrafloral Nectaries of Ricinus communis

The characteristics of nectar secretion by excised extrafloralnectaries of Ricinus have been examined. Secreted nectar wasfound to contain three sugars: sucrose, glucose and fructose,with glucose and fructose occurring in a 1: 1 ratio. All threesugars supported secretion when used in the culture medium andthe yield of nectar sugar was found to be concentration-dependent.Other sugar sources failed to support secretion. Experimentsusing ¹⁴C-sugars and ¹⁴CO₂ fed to intact plants allowed themovement of sugars through the nectary to be examined. Sucrosesynthesis occurs when excised glands are fed glucose and thisoccurs very early in the transport through the nectary. Themain sugar transported was sucrose, with little hydrolysis occurringuntil the final step of secretion. There was no evidence thatsucrose hydrolysis occurs either by invertase in the nectaror by a microbial flora. Inhibitors of respiration were foundto inhibit secretion as did anaerobiosis. Temperature also hada marked effect, with a temperature coefficient of 1.8. However,secretion of sucrose was not affected by anaerobic conditions,low temperatures or inhibitors of respiration as markedly asthat of glucose and fructose. Electron microscopy revealed the presence of a thickened andheavily stained wall at the inner border of the secretory epidermallayer. This wall contained numerous plasmodesmata at a frequencyof 14 per µm² and may represent an apoplastic barrier.Light microscope cytochemistry revealed that acid phosphataseis primarily located in the nectiferous tissue, while ATPaseis concentrated in the epidermis. The possibility that the nectarycontains two pathways for sucrose secretion, both apoplasticand symplastic, is discussed. Key words: Invertase, nectary, plasmodesmata, Ricinus communis, sucrose     

The Role of the Scutellum of Cereal Seedlings in the Synthesis and Transport of Sucrose

Experiments with carbon-labeled glucose and fructose and organsof wheat and barley seedlings suggest that glucose is absorbedfrom the endosperm by the scutellum in germinating grain, simultaneouslyconverted to sucrose, and transported in this form to the seedling.The main lines of evidence which support these conclusions are(1) the level of sucrose in the scutellum is high and that ofthe free hexose low; the reverse is true of the endosperm and,to a lesser extent, of the root and shoot,(2) both isolatedand attached scutella absorb hexose readily and convert it largelyto sucrose under a variety of condition; roots and shoots behavedifferently, (3) more ¹⁴C is accumulated into sucrose by isolatedscutella than by those attached to seedlings, (4) the presenceof enzymes which can effect conversion of hexose to sucrosehas been demonstrated in scutellum extracts. This last bodyof evidence has also supported the view that sucrose synthesisin plants occurs by the pathway mediated by uridine diphosphateglucose as all the relevant enzymes have been detected in asingle extract.     

Modulation of Sucrose Content by Fructose 2,6-bisphosphate during Photosynthesis in Rice Leaves Growing at Different Light Intensities

Reddy, A. R. and Das, V. S. R. 1987. Modulation of sucrose contentby fructose 2,6-bisphosphate during photosynthesis in rice leavesgrowing at different light intensities.—J. exp. Bot. 38:828–833. The relationship between the rate of CO₂ fixation and sucroseconcentration in the leaves of rice (Oryza sativa L.) grownat different light intensities was investigated. Maximum sucrosecontent coincided with maximum rates of CO₂ fixation, achievedat a photon flux density of 1600 µmol m^–2 s^–1.The levels of sucrose and fructose 2,6-bisphosphate were alsocompared in the leaves under different light intensities. Fructose2,6-Msphosphate accumulated during growth at low light. Theactivity of fructose-6-phosphate 2-kinase was high in the leavesgrown at low light while that of fructose-2,6-bisphosphatasewas low. The activities of phosphoglucose isomerase and phospho-glucomutasewere slightly increased by growth at low light The activitiesof UDP glucose pyrophosphorylase were adversely affected invitro with increased concentrations of fructose 2,6-bisphosphatewhile those of sucrose phosphate synthase were moderately affected.Phosphoglucose isomerase and phosphoglucomutase were activatedby fructose 2,6-bisphosphate (8-0 mmol m^–3) by 12-15%.The results suggested that low light intensities during growthresult in an accumulation of fructose 2,6-bisphosphate whichmodulates the key enzymes of sucrose biosynthesis thus regulatingcarbon flow under conditions of limited photosynthesis. Key words: Oryza sativa, photosynthesis, sucrose synthesis, fructose 2,6-bisphosphate, light     

Biosynthesis of ethylene in sweet potato root tissue

The biosynthetic pathway of ethylene in freshly cut and blackrot-diseased tissues of sweet potato roots was investigated.Glucose-U-¹⁴C administration gave labeled ethylene in both freshand diseased tissues, but at the early stage of infection, therewas ethylene production which was not derived from the fed ¹⁴C-glucose.Acetate-1-¹⁴C and acetate-2-¹⁴C were equally incorporated intoethylene produced from fresh tissue, but acetate-2-¹⁴C was preferentiallyincorporated into ethylene from diseased tissue. Pyruvate-3-¹⁴Cwas more efficient as a precursor than was acetate or glucosein fresh tissue, while its efficiency was the same as that ofacetate in diseased tissue. Monofluoroacetate promoted pyruvate-3-¹⁴Cincorporation in fresh tissue but inhibited incorporation indiseased tissue. We concluded that the TCA cycle is involvedin the case of diseased tissue but not in fresh tissue; thus,showing different pathways for ethylene production in each tissue.In addition, in diseased tissue, ethylene is assumed to be producedfrom some cellular component(s), not easily synthesized fromglucose through fungus infection, but is degraded as soon asinfection commences. ¹This paper constitutes Part 85 of the Phytopathological Chemistryof Sweet Potato with Black Rot and Injury ²Present address: The Institute for Biochemical Regulation,Faculty of Agriculture, Nagoya University, Chikusa, Nagoya 464,Japan (Received April 20, 1970; )     

Formation of putrescine from ornithine and arginine in tobacco plants

Putrescine was formed when both DL-ornithine-2-¹⁴C and L-arginine-U-¹⁴Cwere injected into tobacco plants. The incorporation rate ofthese amino acids into putrescine was higher in potassium orsulfur deficient plants than in normal plants. Degradation ofputrescine-1,4-¹⁴C injected into tobacco plants was inhibitedby a potassium or sulfur deficiency. Increased accumulationof putrescine in potassium or sulfur deficient plants may bepartly dependent upon this inhibition in the degradation ofputrescine. Detached leaves and roots were also able to formputrescine from DL-ornithine-2-¹⁴C and L-arginine-U-¹⁴C. (Received December 13, 1968; )     

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.     

Uptake and Metabolism of Sugars by Suspension Cultured Catharanthus roseus Cells

The uptake and metabolism of sugars by suspension-cultured Catharanthusroseus cells were investigated. Substantially all the sucrosein the culture medium was hydrolyzed to glucose and fructosebefore being taken up by the cells. The activity of invertasebound to cell walls, determined in situ, was high at the earlystage of culture. Glucose was more easily taken up by the cellsthan was fructose. Tracer experiments using [U-¹⁴C]glucose and[U-¹⁴C]fructose indicated that glucose is a better precursorfor respiration than fructose, while fructose is preferentiallyutilized for the synthesis of sucrose, especially in the earlyphase of cell growth. Possible metabolic routes of sugar insuspension-cultured Catharanthus roseus cells are discussedin the context of these results. Catharanthus roseus, Madagascar periwinkle, suspension culture, sucrose, glucose, fructose, metabolism, glycolysis     

Pinitol occurrence in soybean plants as affected by temperature and plant growth regulators

Unsuitable temperatures are frequently encountered by soybean(Glycine max L. Merr.) plants grown in the field. Certain polyolshave been reported to protect plants from high temperature orfrost damage. Controlled environment studies were conductedto investigate the effect of stressful temperature regimes onthe content of pinitol (3-O-methyl-D-chiro-inositol) in soybeanplants. Hydroponically-grown soybean plants were subjected tohigh (35/30 C) or low (15/10 C) day/night temperature stresses,and pinitol content in different plant parts was determinedusing high performance liquid chromatography (HPLC). A syntheticplant growth regulator, PGR-IV, was foliarly applied to theplants to evaluate its effect on pinitol content in differentplant components. Uniformly-labelled ¹⁴C-glucose was fed intothe leaves via the transpiration stream, and the effects ofhigh temperature and EXP-S1089, another synthetic plant growthregulator, on the incorporation of ¹⁴C-glucose into pinitolwas evaluated using HPLC separation and scintillation spectrometry.High-temperature stress significantly increased plant pinitolcontent and the incorporation of ¹⁴C-glucose into pinitol, butdecreased the content of sucrose, glucose and fructose. Underlow-temperature stress, there was hardly any change in pinitolcontent, but a drastic increase in soluble sugars. PGR-IV enhancedpinitol translocation from leaves to stems and roots, whileEXP-S1089 increased pinitol/sucrose ratio. Accumulation of pinitolmay be an adjustment mechanism of the plant to reduce high-temperaturedamage, but not low-temperature injuries. Key words: Pinitol, soybean, temperature, plant growth regulator     

The Sugars Concerned in the Tangential Movement of 14C-labelled Assimilates in Willow

Analysis of bark sectors through which tangential movement hadoccurred showed that sucrose was present in greater quantitiesthan glucose or fructose. No evidence could be gained from suchanalyses, however, as to which of these three sugars was themobile species. The use of ¹⁴CO₂ supplied to the leaves, revealed that after24 hours of tangential movement, the greatest proportion ofthe activity in the bark sectors was present in sucrose. Byprogressively reducing the time during which tangential movementwas allowed to occur in these tracer experiments, a patternof results was obtained which completely supports the assumptionthat ¹⁴C-labelled assimilates are transported in a tangentialmanner round the stem as sucrose. The presence of activity inglucose and fructose is merely due to their production fromlabelled sucrose.     

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; )     

Synthesis of L(+) Tartaric Acid from 5-Keto-D-gluconic Acid in Pelargonium

5-Keto-D-[1-¹⁴C]gluconic acid, the most effective precursorof L(+)tartaric acid among all labeled compounds which haveever been tested in grapes, was found to be a good precursorof L(+)tartaric acid in a species of Pelargonium. The synthesisof labeled L(+)tartaric acid from D-[1-¹⁴C]glucose in Pelargoniumwas remarkably depressed when a 0.5% solution of D-gluconateor 5-keto-D-gluconate was administered continuously to leavestogether with D-[1-¹⁴C]glucose. Our results provide strong evidence that D-[1-¹⁴C]glucose ismetabolized in Pelargonium to give labeled L(+)tartaric acidvia (probably D-gluconic acid and) 5-keto-D-gluconic acid withoutpassing through L-ascorbic acid. Labeled L-idonic acid was found in young leaves of Pelargoniumwhich had been labeled with L-[U-¹⁴C]ascorbic acid. The synthesisof the labeled L-idonic acid increased when a 0.1% solutionof L-threonate was administered continuously to leaves togetherwith L-[U-¹⁴C]ascorbic acid. Specifically labeled compounds, recognized as the members ofthe synthetic pathway for L(+)tartaric acid from L-ascorbicacid via L-idonic acid in grapes, were administered to youngleaves of Pelargonium. Each compound (2-keto-L-[U-¹⁴C]idonicacid, L-[U-¹⁴C]idonic acid, 5-keto-D-[1-¹⁴C]gluconic acid and5-keto-D-[6-¹⁴C]gluconic acid) was partly metabolized, as ingrapes. The metabolic pathway starting from L-ascorbic acidto L(+)tartaric acid via L-idonic acid, however, did not actuallycontribute to the synthesis of L(+)tartaric acid in Pelargoniumprobably because the activity of each metabolic step was muchlower than that observed in grapes. (Received May 28, 1984; Accepted July 30, 1984)     

Import of Sucrose and its Partitioning in the Synthesis of Galactomannan and Raffinose-oligosaccharides in the Developing Guar (Cyamopsis tetragonolobus) Seed

Import of sucrose and its transformation to galactomannan andraffinose-oligosaccharides have been studied in the developingguar seed. The amount of galactomannan gradually increased withthe ageing of the seed. During the entire period of pod development,sucrose constituted the major portion of the free sugars inthe seed (both endosperm and cotyledons) as well as in the podwall. Besides myo-inositol, the free sugars detected in thedeveloping endosperm and cotyledons were glucose, fructose,raffinose and stachyose. Some compounds, possibly glycosides(RG values higher than that of fructose), were also detectedin the endosperm. In the later stages of seed development, therelative proportion of raffinose in the free sugars increased,reaching 50% of the total free sugars in 77-d-old cotyledons.With pod maturity, the activities of soluble acid and boundacid invertases in the pod wall increased manifold with a concomitantdecline in the non-reducing sugar content. These enzymes seemto be involved in the mobilization of sucrose from this fruitingstructure into the seed. An increased synthesis of raffinose-oligosaccharidesboth in the endosperm and cotyledons was associated with highactivities of soluble acid invertase (pH 4.8) and sucrose-UDPglucosyl transferase in these tissues. Feeding uniformly labelled¹⁴C-sugars to the detached intact pods as well as to the isolatedendosperm and cotyledons resulted in labelling of all endogenousfree sugars and galactomannan. The uptake and incorporationinto galactomannan of ¹⁴C was stimulated by Co²⁺, Mn²⁺ and Mg²⁺.Except for mannose, a major proportion of the ¹⁴C from glucose,fructose and sucrose appeared in sucrose in both endosperm andcotyledons indicating a fast reconstitution of sucrose in situ.Based on the present results, a possible mode of transformationof sucrose to galactomannan and raffinose-oligosaccharides hasbeen proposed. Key words: Sucrose, galactomannan, raffinose-oligosaccharides, invertase, sucrose-UDP glucosyl transferase, ¹⁴C-incorporation, guar seed     

Some factors affecting the concentrations of sugars in leaves of inbred sugar-beet lines

In the glasshouse, large differences in concentrations of glucose and sucrose were observed between leaves of inbred sugar-beet lines that are known to differ from each other in resistance to pests and diseases. Differences between these lines in concentrations of fructose, glucose and sucrose were more pronounced in the petiole than in the lamina. The concentrations of glucose and fructose were lower in the first two leaves (primary leaves) than in those produced subsequently (secondary leaves); both types of leaf contained similar concentrations of sucrose. Secondary leaves from plants that had been kept in darkness for 17 h contained less fructose, glucose and sucrose than those of plants kept in sunlight for 5 h. Longer period of darkness lowered the concentrations of monosaccharides in the leaves further but did not affect the sucrose content. Primary and secondary leaves from the same sugar-beet plant often differ in non-race-specific resistance to pests and diseases; and darkness can affect suscetibility of beet to downy mildew and to the aphid Myzus persicae. The results of the sugar determinations therefore support the hypothesis that the concentrations of certain carbohydrates in sugar-beet leaves are important in non-race-specific resistance to pests and diseases.     

The Relationship between Sucrose Supply, Sucrose-cleaving Enzymes and Flower Abortion in Pepper

Abortion of pepper flowers depends on the light intensity perceivedby the plant and on the amounts of sucrose taken up by the flower(Aloni B, Karni L, Zaidman Z, Schaffer AA. 1996.Annals of Botany78: 163–168). We hypothesize that changes in the activityof sucrose-cleaving enzymes within the flower ovary might beresponsible for the changes in flower abortion under differentlight conditions. In the present study we report that the activityof sucrose synthase, but not of cytosolic acid invertase, increasesin flowers of pepper plants which were exposed, for 2 d, toincreasing photosynthetically active radiation (PAR) in therange of 85–400 µmol m^-2s^-1at midday. Sucrose synthaseactivity increased in parallel with the increasing concentrationsof starch in the flower ovary. Feeding flower explants, preparedfrom 3-d-predarkened plants, with 100 mM sucrose for 24 h, causeda 23% increase in reducing sugars and a 2.5-fold increase instarch concentration, compared with explants fed with buffer.Likewise, feeding explants of pepper flowers with sucrose, glucose,fructose and also mannitol increased the sucrose synthase activityin the ovaries. Concomitantly, sucrose, glucose and fructose,but not mannitol, reduced the abortion of flower explants. Itis suggested that sucrose entry into the flower increases theflower sink activity by inhibiting abscission and inducing metabolicchanges, thus enhancing flower set. Pepper; Capsicum annuum L.; abscission; light; pepper flowers; sucrose; glucose; fructose; starch; acid invertase; sucrose synthase     

BIOGENESIS OF ETHYLENE IN APPLE TISSUE: I. FORMATION OF ETHYLENE FROM GLUCOSE, ACETATE, PYRUVATE, AND ACETALDEHYDE IN APPLE TISSUE

1. With the aim of elucidating the path of carbon in the formationof ethylene in plants, studies were made on the incorporationof ¹⁴C into ethylene evolved from apple slices, using several¹⁴C- labeled compounds as substrates. The effects of inhibitorswere also investigated. 2. The formation of ethylene-¹⁴C from glucose-¹⁴C was inhibitedby fluoride, but unaffected by arsenite, thus suggesting thatglucose is converted to ethylene via pyruvate. 3. Acetate is converted to ethylene after cleavage of C-l andC-2. Only a small portion of the latter (C-2) enters the moleculeof ethylene, the former (C-l) is detected in carbon dioxide.On the other hand, 2, and 3-carbons of pyruvate are converted,without splitting, to ethylene. 4. On removal of air, the incorporation of ¹⁴C into ethylenefrom acetate-2-¹⁴C was depressed, while that from pyruvate-¹⁴Cwas unaffected. 5. Acetaldehyde-l,2-¹⁴C is converted to ethylene without conversioninto ethanol. 6. These results are interpreted to suggest the occurrence ofthe pathway in which pyruvate and acetaldehyde may serve asprecursors of ethylene. ¹ A part of this paper was read at the regular Meeting of KansaiBranch of the Agricultural Chemical Society of Japan in Kyoto,October, 1964, and at the Annual Meeting of the Japanese Societyof Plant Physiologists in Tokyo, April, 1965 and presented ina preliminary form elsewhere (10).     

Long-term Metabolism of [14C]Sugars in Stored Potatoes

[¹⁴C]Sucrose, [¹⁴C]glucose and [¹⁴C]fructose were introducedinto potato tubers held at 10 °C and the redistributionof label chased over a 65 d period in storage. Respiratory losseswere identical in all treatments, as was the partitioning of¹⁴C between soluble and insoluble forms. Sucrose was the predominantlabelled sugar in the tubers after 20 h, regardless of the original[¹⁴C]sugar introduced, and was loaded and distributed throughoutthe tubers by the internal phloem system. After 20 h the proportionsof labelled sugars bore no relationship to those of the unlabelledendogenous sugars. However, with time the percentage of ¹⁴Cin sucrose fell while that in glucose increased and by 65 dthe proportions of the labelled sugars more closely resembledthe endogenous pools. Fructose represented a consistently lowproportion of both the labelled and unlabelled sugars. By 21d a considerable proportion of the soluble ¹⁴C had been convertedto starch (approx. 25% of the total tuber 14C), this value remainingrelatively constant for the remainder of the storage period.Sprouts which formed on the tubers contained up to 6% of thetotal tuber ¹⁴C but less than 0.2% of the tuber dry matter.It is suggested that the bulk of the translocated [¹⁴C]sucroseentered the symplast and exchanged slowly with the bulk of thesugars in the storage cell vacuoles. [¹⁴C]sugars, phloem loading, starch, potato tuber, Solunum tuberosum, cold storage