Alicyclic acid metabolism in plants 3. Fate of 14C-shikimate and 14C-quinate in mung bean plants

Young mung bean plants (Phaseolus mungo) were exposed to ¹⁴C-shikimateor ¹⁴C-quinate in the light. After 8 or 23.5 hr of incubationat 25°C, radioactivities in free and bound amino acids,organic acids, soluble and insoluble carbohydrates, ether-solublefraction and lignin were determined. Shikimic and quinic acidswere separated by the combined use of paper-chromatography andcolumn chromatography. Specific activity of formed quinate orshikimate was only slightly lower than that of fed shikimateor quinate. Specific activities of phenylalanine, tyrosine andbound tryptophan were high as compared with those of non-aromaticamino acids. Discussion is focused upon the interconversionbetween shikimate and quinate, and their roles in the biosynthesisof aromatic amino acids. (Received November 15, 1968; )     

Pathways of Utilization of [1-14C] Glucose and [6-14C] Glucose in Slices of Peas

Slices of ripening seeds of the pea (Pisum sativum) were suppliedwith [1-¹⁴C] G and [6-¹⁴C] G, and the S.A. was determined ofthe respirod carbon dioxide, pyruvate, and the acids of theT.C.A.C. as well as that of the individual carbon atoms of citrateand malate. The possibility that there exist active and inactive pools ofthe T.C.A.C. acids in the pea is considered and, for most ofthe acids, rejected. The results cannot be explained on the bais of the T.C.A.C.because the S.A. of the carbon dioxide liberated was some tentimes higher than could have come from the malate via the T.C.A.C.,too much ¹⁴C accumulated in the cycle acids to have come frompyruvate by the operation of the T.C.A.C., and the patterrnof label in citrate and malate was different from that expected. An alternative explanation is put forward based on the oxidationof glucose by the P.P.P. and movement of ¹⁴C by a series ofrapid isotope exchange reactions.     

Turnover of Shikimate Pathway Metabolites during Shoot Initiation in Tobacco Callus Cultures

The turnover of shikimate pathway intermediates and end productswas examined in tobacco (Nicotiana tabacum L. Wisconsin 38)callus cultured under shoot-forming and non-shoot-forming conditions.In shoot-forming tissue there was a higher rate of net synthesisof quinic and shikimic acids than in proliferating callus. Post-incubation,there was a decrease in labeled quinate and an increase in shikimate.The changes in activity of quinate:NAD^$ oxidoreductase werein agreement with the above. The aromatic amino acids, tyrosine,phenylalanine and tryptophan, showed little turnover in theproliferating tissues. On the other hand, higher rates of netsynthesis and degradation, mainly of tyrosine, were observedin shoot-forming tissues. These findings are discussed in relationto the shoot-initiation process. (Received October 14, 1983; Accepted June 4, 1984)     

The Partitioning of Photosynthetically Assimilated 14C into Amino Acids in Wheat 1. Partitioning During Transport to the Grain

When ¹⁴CO₂ was fed to flag leaf laminae at 20 d post-anthesis,the transport organs between the leaf and the grains containedappreciable ¹⁴C in glutamine, glutamate, serine, alanine, threonineand glycine. Smaller amounts of ¹⁴C were present in gamma-aminobutyricacid (GABA), aspartate and cysteine. Other amino acids whichwere labelled in the source leaf were not labelled in the transportorgans. The export of labelled glutamine, serine, glycine andthreonine from the source leaf was favoured in comparison tothe other amino acids mentioned. Threonine accumulated, andwas subsequently metabolised, in the rachis. [¹⁴C]GABA alsoaccumulated in the rachis. In the grains, the relative amountof soluble [¹⁴C]alanine increased with chase time. This wasprobably due to de novo synthesis and reflected the specialrole of alanine in grain nitrogen metabolism. Wheat, Triticum aestivum, ¹⁴CO₂, amino acids, transport, carbon metabolism     

Metabolism of Inorganic Carbon Taken Up by Roots in Salix Plants

The metabolic products of inorganic carbon taken up throughthe roots from nutrient solution were studied in willow plants.Willow cuttings (Salix cv. Aquatica gigantea) were suppliedwith unlabelled or ¹⁴C-labelled NaHC0₃ for 1, 5, 10, and 24h in light or in darkness. After feeding, the plants were dividedinto six samples (upper and lower leaves and corresponding stems,cuttings and roots), which were frozen in liquid N₂. Freeze-driedground samples were extracted into water-soluble, chloroform-solubleand insoluble fractions. The water-soluble fraction was furtherseparated into basic, acidic, and neutral fractions by ion-exchangechromatography. In the light experiment pronase treatment wasused to separate the insoluble fraction into proteins and insolublecarbohydrates. After I h feeding time, most of the ¹⁴C was fixed into organicacids and amino acids both in light and in darkness in all partsof the plants. In the roots a large part of the ^l4C-carbon wasincorporated into the protein and insoluble fractions alreadyduring short feeding times, and the amounts incorporated increasedwith time. In the leaves, after 1 and 5 h the main labelledcompounds were the organic acids and amino acids, but after10 h about half of the total ¹⁴C was in protein and in the insolublefraction. A further analysis of amino acids and organic acidswith HPLC showed that C-4 acids were labelled initially andthat over time the proportion of different acids changed. These results indicate that the metabolism of carbon in rootsmight take place via ß-carboxylation of PEP. Partof the fixed ¹⁴C is transported from the roots, probably asamino acids and organic acids, to the shoot. In roots the C-4acids are metabolized further into structural compounds (proteinsand insoluble carbohydrates). Key words: DIC, Salix, roots, metabolism, HPLC     

Biosynthesis of Acyl Moieties of Capsaicin and its Analogues from Valine and Leucine in Capsicum Fruits

Biosynthetic pathways of acyl moieties of capsaicinoid in intactCapsicum fruits and spheroplasts prepared from placentas ofCapsicum fruits were examined using a radioisotopic technique.In intact Capsicum fruits, L-[U-¹⁴C] valine was incorporatedinto capsaicin and dihydrocapsaicin, the acyl constituents ofwhich are even-number branched chain fatty acids, while L-[U-¹⁴C]leucine was incorporated into nordihydrocapsaicin and homodihydrocapsaicin,which have odd-number branched chain facty acids as the acylmoieties. The intermediates of the odd- and even-number branchedchain fatty acids were identified with GLC/GPC after the spheroplastshad been incubated with L-[U-¹⁴C] valine or L-[U-¹⁴C] leucine.After incubation with L-[U-¹⁴C] valine, isobutyric acid and8-methyl nonanoic acid were detected, while isopentanoic acidand 9-methyl decanoic acid were found after incubation withL-[U-¹⁴C] leucine. The involvement of a-ketoisovalerate or a-ketoisocaproatein the biosynthesis of acyl moieties of capsaicinoid was alsodemonstrated in vitro using cell-free extracts of the placentasof Capsicum fruits. These findings suggest that the acyl moietiesof individual capsaicinoids in Capsicum fruits are synthesizedby pathways similar to those proposed for adipose tissue andbacteria. ¹Formation and Metabolism of Pungent Principle of Capsicum Fruits.Part IX. (Received September 2, 1980; Accepted November 17, 1980)     

Biosynthesis of alicyclic acids from 14C-labeled glucose and erythrose by isolated cells from Vigna angularis leaves

Mesophyll cells isolated enzymatically from Vigna angularisleaves were fed ¹⁴Cglucose or ¹⁴C-erythrose and the time-courseof ¹⁴C incorporation into shikimic and quinic acids was examined.When ¹⁴C-glucose was fed to the cells, the highest radioactivityin quinic acid was observed after 10 hr of incubation, whilethat in shikimic acid was after 14 hr. In the experiment with¹⁴C-erythrose, the radioactivity in shikimic acid rose strikinglyup to the 3rd hour, but ¹⁴C in quinic acid increased graduallyduring the incubation. The incorporation of ¹⁴C into shikimicacid was enhanced when unlabeled shikimic or quinic acid wassupplied to the cells simultaneously with either ¹⁴C-glucoseor ¹⁴G-erythrose, whereas that into quinic acid was not significantlyincreased by these alicyclic acids. The difference in incorporationrate of ¹⁴C into quinic acid from that into shikimic acid wasmore conspicuous in the isolated mesophyll cells than in theepicotyls of V. angularis seedlings. ¹ Present address: Department of Biology, Faculty of Science,Kumamoto University, Kumamoto 860, Japan. (Received September 22, 1978; )     

Short-term Products of 14C-acetate Assimilation by Chlorella pyrenoidosa in the Light

The kinetics of ¹⁴C-2-acetate assimilation by Chlorella pyrenoidosain the light were examined. Under aerobic conditions the primaryproduct of acetate assimilation was succinic acid which, afterten seconds, contained over 60 per cent of the ¹⁴C incorporatedby the cells. The percentage of the total ¹⁴C in succinate fellwith time, while that in citrate and glutamate increased. After1800 sec over 60 per cent of ¹⁴C was present in two compounds,glutamic acid and an unknown compound (X). Glucose-6-phosphate,fructose-6-phosphate, phosphoglyceric acid and phosphoenolpyruvicacid became labelled after 60 sec but together never containedmore than one per cent of the total ¹⁴C incorporated. Underanaerobic conditions succinate was still the primary productof acetate assimilation, and the absence of carbon dioxide resultedin a decrease in ¹⁴C incorporation into compound X. The patternof acetate assimilation in acetate grown and acetate adaptedChlorella was very similar to that in photo-autotrophicallygrown Chlorella. In the presence of 10^–6M DCMU, succinicacid was the primary product of acetate assimilation, but therewas an early Incorporation of ¹⁴C into glutamate, aspartate,and malate. 4 x10^–3M MFA did not effect the early incorporationof ¹⁴C into succinic acid, but resulted in accumulation of ¹⁴Cin citrate and a decreased amount in glutamate and in compound X.     

Formation of L-(+)-Tartaric Acid in Leaves of the Bean, Phaseolus vulgaris L.: Radioisotopic Studies with Putative Precursors

The biosynthetic pathway from D-glucose to L-(+)-tartaric acid(TA) in detached leaves of the bean, Phaseolus vulgaris L.,was studied in three cultivars, two of which were known to containTA and one of which lacked TA, with the aid of several putativeradiolabeled intermediates, namely D-[l-¹⁴C]glucose, D-[6-¹⁴C]glucose,D-[U-¹⁴C]glucose, D-[U-¹⁴C]gluconate, L-[U-¹⁴C]-ascorbic acid,L-[l-^l4C]idonate, D-xylo-5-[U-¹⁴C]hexulosonate, D-xylo-5-[l-¹⁴C]hexulosonate,D-xylo-5-[6-^l4C]hexulosonate and L-[U-^l4C]threonate. D-[U-¹⁴C]Glucoseand D-[U-^l4C]gluconate were converted to TA with low isotopicyield but this yield was further reduced when leaf tissues weresupplied with unlabeled D-gluconate or D-xylo-5-hexulosonate.D-xylo-5-[U-¹⁴C]Hexulosonate and D-xylo-5-[l-¹⁴C]hexulosonatewere good precursors of TA. D-xylo-5-[6-¹⁴C]Hexulosonate didnot furnish ¹⁴C to TA. Addition of a metabolic product of D-xylo-5-hexulosonate(which was labeled by D-xylo-5-[l-¹⁴C]hexulosonate but not byD-xylo-5-[6-¹⁴C]hexulosonate) to leaves labeled with D-xylo-5-[l-¹⁴C]hexulosonatedoubled the incorporation of ¹⁴C into TA. L-[U-¹⁴C]Ascorbicacid, L-[l-¹⁴C]idonate and L-[U-¹⁴C]threonate failed to producelabeled TA. A metabolic scheme to accommodate these observationsis presented. (Received October 21, 1988; Accepted March 29, 1989)     

Effect of shade treatment on biosynthesis of catechins in tea plants

When tea plants were shaded with black lawn cloth for severaldays in the field, the accumulations of (—)-epicatechin,(—)-epicatechin-3-gallate, (—)-epigallocatechinand (—)-epigallocatechin-3-gallate decreased in newlydeveloping tea shoots. Radioactive tracer studies showed thatthe conversions of glucose-U-¹⁴C, shikimic acid-G-¹⁴C and phenylalanine-U-¹⁴Cinto (—)-epicatechin and (—)-epigallocatechin moietieswere depressed by the shade treatment for tea plants but theincorporation of trans-cinnamic acid-3-¹⁴C was not affected.The treatment was found to have no significant effect on theactivities of phospho-2-keto-3-deoxy-heptonate. aldolase (EC.4.1.2.15 [EC] ), 3-dehydroquinate synthase (EC. 4.6.1.3 [EC] ), 3-dehydroquinatedehydratase (EC. 4.2.1.10 [EC] ), shikimate dehydrogenase (EC. 1.1.1.25 [EC] )and trans-cinnamate 4-monooxygenase (EC. 1.14.13.11 [EC] ) in theshoots, whereas the activity of phenylalanine ammonia-lyase(EC. 4.3.1.5 [EC] ) clearly decreased. (Received March 17, 1980; )     

Mobilization of Reserves and Synthesis of Sterols and Triterpenes in Seedlings of Two Canarian Euphorbia Species

Seedlings from Euphorbia canariensis and Euphorbia lambii weregrown in the dark at 25 °C. Protein and triglyceride contentas well as levels of sugars and amino acids in the endospermwere determined during endosperm depletion. In the endospermof Euphorbia canariensis, relatively low levels of amino acids(up to 1 µmol.endosperm^–1) were found of which glutamine/glutamateaccounted for 40% at the stage of radicle emergence. High levelsof amino acids (up to 4 µmol.endosperm^–1) comparedwith sugars (up to 2 µmol sucrose.endosperm^–1) weredetected in the endosperm of Euphorbia lambii. Arginine wasthe main component (28 µmol%) of the amino acids in thistissue. In both species amino acid composition changed graduallyduring endosperm depletion. Cotyledons retained their ability to absorb a variety of watersoluble substrates after removal of the endosperm. ¹⁴C from[U-¹⁴C]sucrose was effectively incorporated into the triterpenesof the laticifers and to a lesser extent into the sterols ofthe seedling. The highest incorporation values were found inyoung seedlings about 2 d after the emergence of the radicle.Seedlings of this age also showed high incorporation rates of¹⁴C from labelled alanine, serine, threonine, valine, leucineand isoleucine into both triterpenols and sterols, but no generalconclusions about metabolic channelling in lipid synthesis couldbe made. Endosperm, Euphorbia canariensis L. Euphorbia lambii Svent., sterols, triterpenols, amino acids, laticifer, biosynthesis     

Radiolabelling Studies of Lipids in the Marine Cryptomonad Chroomonas salina in Relation to Fatty Acid Desaturation

Cells of Chroomonas salina were exposed to [¹⁴C]acetate, [^l4C]16:0,[¹⁴C]18:0, [¹⁴C]18:1(n-9), [¹⁴C]18:2(n–6) or [¹⁴C]18:3(n–3)for 1 h and then incubated for 24 h in non-radioactive medium.At the end of the pulse period, non-glycolipid polar lipidscontained the highest proportions of radioactivity incorporatedfrom [¹⁴C]acetate and [¹⁴C]18:3(n–3) whereas with [¹⁴C]16:0,[¹⁴C]18:1 and [¹⁴C]18:2(n–6), triacylglycerols were mosthighly labelled. ¹⁴C-18:0 was recovered mainly as non-esterifiedfatty acid. Monogalactosyldiacylglycerol initially contained17% of label incorporated from [¹⁴C]acetate but less than 3%of that from [¹⁴C]fatty acids. With all substrates, excluding[¹⁴C]18:0, a gradual transfer of label from polar lipids totriacylglycerols was observed during the chase period. Saturatesand monoenes synthesised from [¹⁴C]acetate were mostly transferedfrom phospholipids and glycolipids to neutral lipid withoutfurther desaturation. Most of the incorporated ¹⁴C-fatty acidsremained unchanged and only with [¹⁴C]18:3(n–3) was substantialamounts of label recovered in penta- and hexaenoic fatty acids.The results indicate that, under the conditions of the study,lipid synthesis in the algae was heavily dominated by triacylglycerolformation and that the mechanisms of fatty acid desaturationin this species may differ from those in higher plants. (Received December 10, 1991; Accepted March 6, 1992)     

Further studies on the metabolism of glucose in the process of "glucose-bleaching" of Chlorella protothecoides

Previous studies have demonstrated that when cells of Chlorellaprotothecoides are incubated in a medium containing glucosebut no nitrogen source, they are profoundly bleached with degenerationof chloroplast structure and photosynthetic activity. When anitrogen source (urea) is added to the glucose medium, bleachingof algal cells is greatly suppressed. In this work the metabolismof glucose in the process of glucose-induced bleaching was studiedusing ¹⁴C-glucose as tracer. Changes in algal cell activityfor ¹⁴CO₂-evolution and ¹⁴C-incorporation into various cellularsubstances from ¹⁴C-glucose were followed. Most conspicuouswere increases in cellular activities for assimilating ¹⁴C-glucoseinto lipids (fatty acids) and glucose polymer. When urea wasadded to the glucose medium, the incorporation of ¹⁴C by algalcells into fatty acids was greatly reduced, while the assimilationof ¹⁴C into glucose polymer was increased. These and previous observations suggest that the formation oflarge amounts of lipids (fatty acids) probably is causally relatedto the induction of algal cell bleaching. (Received March 5, 1969; )     

Alicyclic acid metabolism in plants V. Biosynthesis of alicyclic acids from 14C-labeled glucose and erythrose in some plant tissues

Etiolated seedlings of Phaseolus mungo were fed with ¹⁴C-glucoseand the incorporation of ¹⁴C into shikimic and quinic acidswas determined. The incorporation of ¹⁴C into shikimic acidwas enhanced when non-labeled shikimic, quinic or 5-dehydroquinicacid was not significantly affected by these alicyclic acids.To examine whether the difference in biosynthetic patterns betweenshikimic and quinic acids is common in higher plants, flowersand leaves of several plants were fed with ¹⁴C-glucose or ¹⁴C-erythroseand the effciencies of these labeled sugars as precursors ofshikimic and quinic acids were compared. In seven of eight plantsamples, erythrose was superior to glucose as the precursorof shikimic acid, while there was no great difference in theefficiency of either sugar as the precursor of quinic acid.The possibility that the biosynthetic mechanism for quinic aciddiffers from that for shikimic acid is discussed. (Received September 12, 1973; )     

Metabolism of C1 unit precursors in Neurospora: Effects of media supplements on labelling of nucleic acids and protein

Mycclia of Neurospora crassa wild type (FE SC no. 853), harvestedduring the exponential phase of growth on defined minimal mediaincorporated glycine-2-¹⁴C, serine-3-¹⁴C and formate-¹⁴C intoproteins, DNA and RNA. Supplementing the growth medium with1 mM glycine increased the flow of glycine and formate carboninto these products. In contrast, this supplement decreasedthe incorporation of serine-¹⁴C. When such cultures were preincubatedfor 30 min with adenine, formaldehyde, formate or L-methionine,labelling of the nucleic acids and protein fractions by glycine-2-¹⁴Cwas altered. It is concluded that glycine increases the turnoverof C₁ units in Neurospora, resulting in greater contributionsof the C-2 in nucleic acid and protein synthesis. (Received May 14, 1977; )     

The Oxidation of 14C-labelled Glucose by Chlorella vulgaris: 1. The Time Course of 14CO2 Production

Glucose, either uniformly labelled with¹⁴C, or specificallylabelled in the I, 2, or 6 position, was added to C. vulgaris.Radio-active carbon dioxide was produced initially ten timesfaster from glucose-I-¹⁴C than from glucose-6-¹⁴C. This differencewas found with carbohydrate-starved cultures, exponentiallygrowing cultures, and cultures assimilating ammonia or nitraterapidly. A similar difference was also found with C. pyrenoidosaand Ankistrodesmus. 37 per cent. of the ¹⁴C added as glucose-¹-¹⁴Cto exponentially growing cells was recovered as carbon dioxidebut generally the recovery was less than this. Only 5 per cent.of ¹⁴C added as glucose-6-¹⁴C was recovered as carbon dioxide.The specific activity of the carbon dioxide produced was considerablylower than that of the carbon in the added glucose.     

Effect of leaf age on light and dark 14CO2 fixation in a CAM plant, Bryophyllum calycinum

Leaves of different ages from B. calycinum were exposed to ¹⁴CO₂in light during day and night. The labelling pattern on thechromatogram differed with leaf age. Young leaves had similarpatterns to those of C3 plants during both day and night. Matureleaves showed high incorporation of ¹⁴C into C4 acids, especiallyat night. In contrast, no significant difference with leaf agewas observed in the pattern of dark ¹⁴CO₂ fixation products.Study of the enzyme activity and the content of titratable acidat each leaf age suggested that high incorporation of ¹⁴C inC4 acids during the night was due to the simultaneous absorptionof CO₂ by both enzymes RuDPcarboxylase and PEPcarboxylase. (Received November 24, 1977; )     

The Partitioning of Photosynthetically Assimilated 14C into Amino Acids in Wheat: 2. Distribution in Amino Acids of Wheat Grain Fractions

Changes in the distribution of ¹⁴C between free and bound aminoacids in wheat grains (Triticum aestivum L. cv. Arkas) at 10and 20 d post-anthesis are described. After ¹⁴CO₂, labellingof the flag leaf, ¹⁴C was initially more rapidly transferredto the grains of 20 d post-anthesis plants than for 10 d post-anthesisplants. However, after a 460 min chase period in the light theamount of ¹⁴C in the grains of the younger and older plantswere similar. In the younger, more rapidly growing grains, agreater proportion of the ¹⁴C was incorporated into structuraltissue and starch. ¹⁴C accumulation in the grains continuedduring the dark in the younger grains but not in the older grains. Although the overall ¹⁴C distribution between the free aminoacid and protein pools of the grain was similar for both treatments,the distribution within the albumin, prolamin and globulin fractionsand between the individual non-bound amino acids differed. Ofthe protein fractions, the albumins were initially the mostheavily labelled but after 460 min chase the prolamins containedmore ¹⁴C. The majority of the ¹⁴C in the albumin and globulinfractions after 280 min chase was in hydrolysable, non-aminoacid compounds. In both tissues, the free amino acid pools lostradioactivity in the dark but the solid residues and proteinscontinued to function as ¹⁴C sinks. Daily fluctuations in the radioactivity in free and bound alanineare consistent with the role of free alanine as a diurnal metabolicnitrogen pool. Wheat, Triticum aestivum¹⁴CO₂, amino acids, proteins, carbon metabolism     

Metabolism of Pyrimidines in Protoplasts from Cultured Catharanthus roseus Cells

The metabolism of [2-¹⁴C]thymine, [2-¹⁴C]thymidine, [2-¹⁴C]uraciland [¹⁴C]uridine was investigated in protoplasts obtained fromsuspension cultures of Catharanthus roseus. Most of the exogenouslysupplied thymine, thymidine and uracil was degraded, and salvageof these pyrimidines accounted for 5–36 per cent of thetotal amount of ¹⁴C-labelled precursors which was metabolized.However, more than 80 per cent of the labelled uridine was utilizedfor the biosynthesis of nucleotides and nucleic acids, and therest was degraded. In contrast to the results from protoplastsof sugar cane cells in suspension culture, the data indicatethat protoplasts possess a pathway for the degradation of pyrimidines,and that the overall metabolism of these pyrimidines in protoplastsis very similar to the metabolism in the intact cells. Catharanthus roseus, madagascar periwinkle, protoplasts, pyrimidine metabolism     

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)