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)     

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)     

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)     

Biointeraction between precarthamin and cell components in florets ofCarthamus tinctorius L.

The relative rate of precarthamin extractability and floret protein inactivation by organic solvents were compared. Upon trituration of the floral tissues ofCarthamus tinctorius L., usually less extractable precarthamin is released at a markedly high level, while the releasability rate is changed conspicuously by macerating the florets in the test solvents of increased concentrations; the amount of releasable precarthamin also varies according to the solvents used. 30% (v/v) acetone promotes the pigment solubility about twice, whereas, its capacity decreases abruptly in reverse proportion to the increment of acetone content. Methanol accelerates the precarthamin release, but the rate is very low. Ethanol acts in far lesser extent. The data indicate that these varied aspects are more or less attributed to the inactivation of possible factors dissociating precarthamin from cellular components in freezed safflower florets.     

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     

Comparison of the Respiratory Metabolism of Plantago lanceolata L. and Plantago major L.

Bryce, J. H. and ap Rees, T. 1985. Comparison of the respiratorymetabolism of Plantago lanceolata L. and Plantago major L.—J.exp. Bot. 36 1559–1565. The aim of this work was to discover if the respiratory metabolismof the roots of Plantago lanceolata L. differed from that ofthe roots of Plantago major L. Measurements of oxygen uptakeand dry weight of excised root systems during growth of seedlingsprovided evidence that the two species differed in the amountof respiration needed to support a given increase in dry weight.Excised root systems were given a 6-h pulse in [U-¹⁴C]sucrosefollowed by a 16.5-h chase in sucrose. The detailed distributionof ¹⁴C amongst the major components of the roots at the endof the pulse and the chase revealed no significant differencebetween the two species. Patterns of ¹⁴CO₂ production from [1-¹⁴C],[2-¹⁴C], [3,4-¹⁴C], and [6-¹⁴C]glucose of excised root systemsfrom plants of three ages were similar for the two species.It is suggested that there is no conclusive evidence for anysignificant inherent difference in the respiratory metabolismof the roots of the two species. Key words: ¹⁴C sugar metabolism, respiration, roots, Plantago     

Relationship between photosynthetic carbon metabolism and essential oil biogenesis in peppermint under Mn-stress

Changes in growth and yield parameters, and ¹⁴CO₂ and (U-¹⁴C)sucrose incorporation into the primary metabolic pool, and essentialoil have been investigated under Mn-deficiency and subsequentrecovery in Mentha piperita, grown in solution culture. UnderMn-deficiency, CO₂ exchange rate, total chlorophyll, total assimilatoryarea, plant dry weight, and essential oil yield were significantlyreduced, whereas chlorophyll a/b ratio, leaf area ratio andleaf stem ratio significantly increased. In leaves of Mn-deficientplants, ¹⁴CO₂ incorporation into the primary metabolic pool(ethanol-soluble and -insoluble) and essential oil were significantlylower, whereas (U-¹⁴C) sucrose incorporation into these componentswas significantly higher as compared to the control. Among theprimary metabolites, the label was maximum in sugars, followedby organic acids and amino acids. A higher label in these metaboliteswas, in general, observed in stems of Mn-deficient plants ascompared to the control. Mn-deficient plants supplied with completenutrient medium for 3 weeks exhibited partial recovery in growthand yield parameters, and essential oil biogenesis. Thus, underMn-deficiency and subsequent recovery, the levels of primaryphotosynthetic metabolites and their partitioning between leafand stem significantly influence essential oil biogenesis. Key words: Mentha piperita, Mn-stress, ¹⁴CO₂ and [U-¹⁴C] sucrose incorporation, oil accumulation, primary photosynthetic metabolites     

Effects of ABA on Synthesis of Cell-Wall Polysaccharides in Segments of Etiolated Squash Hypocotyl I. Changes in Incorporation of Glucose and myo-Inositol into Cell-Wall Components

Externally supplied [³H]myo-inositol and [¹⁴C]glucose were incorporatedin cell-wall fractions of segments of etiolated squash hypocotyl.The extent of incorporation of [¹⁴C]glucose into cell-wall fractionswas very much greater than that of [³H]myo-inositol. Radioactivityfrom [¹⁴C]-glucose was effectively incorporated into hemicelluloseB and cellulose fractions and was incorporated uniformly intohexose, pentose and uronic acid residues, but radioactivityfrom [³H]myo-inositol was incorporated predominantly into uronicacid and pentose residues in the pectin and hemicellulose Bfractions. Exogenously applied ABA significantly suppressed the elongationof segments of squash hypocotyl and the incorporation of radioactivityfrom [^l4C]glucose and [³H]myo-inositol into the segments. Furthermore,ABA significantly inhibited the distribution of incorporatedradioactivity from [¹⁴C]glucose into the cellulose fraction,but did not affect distribution into the pectic fraction. Bycontrast, ABA only slightly inhibited the distribution of theincorporated radioactivity from [³H]myo-inositol into the pecticfraction. These results suggest that most of the cell-wall polysaccharidesin segments of squash hypocotyl are synthesized via the UDP-sugarpathway, and that ABA significantly inhibits the synthesis ofcellulose but not the synthesis of pectic polysaccharides whenABA suppresses the elongation of the segments. (Received March 25, 1988; Accepted November 15, 1988)     

Xylan Synthase Activity in Isolated Mesophyll Cells of Zinnia elegans during Differentiation to Tracheary Elements

A paniculate fraction obtained from mesophyll cells of Zinniaelegans that were differentiating into tracheary elements exhibitedxylan synthase activity, catalyzing the transfer of ^MC-xylosefrom UDP-D-[U-¹⁴C]-xylose into 1,4-linked xylan. The activityincreased transiently at the same time as thickening of secondarycell walls occurred, a process that is accompanied by the depositionof cellulose, xylan and lignin. (Received August 3, 1990; Accepted December 6, 1990)     

Isolation of 1-O-trans-p-Coumaroyl-r{beta}-D-glucopyranose from Sweet Potato Roots and Examination of Its Role in Chlorogenic Acid Biosynthesis

1-O-trans-p-Coumaroyl-rß-D-glucopyranose (p-coumaroyl-D-glucose)was isolated from slices of sweet potato root which had beenincubated with trans-cinnamic acid. Pre-loaded trans-cinnamicacid efficiently trapped the radioactivity from L-[U-¹⁴C]-phenylalanineand reduced its incorporation into chlorogenic acid by 75% ofcontrol values in disks of sweet potato root. In the root diskssupplied with trans-[3-¹⁴C]-cinnamic acid, the radioactivitywas transferred first to trans-cinnamoyl- D-glucose, then top-coumaroyl-D-glucose, and subsequently to chlorogenic acidand isochlorogenic acid. These results support our earlier propositionthat p-coumaroyl-D-glucose is involved in the biosynthesis ofchlorogenic acid as an intermediate adjacent in the pathwayto trans-cinnamoyl-D-glucose in sweet potato roots. (Received April 11, 1988; Accepted August 9, 1988)     

Compensatory Aspects of the Biosynthesis of Spermidine in Tobacco Cells in Suspension Culture

The relationship between the biosynthesis of polyamines andethylene was examined in suspension cultures of Nicotiana tabacumL. cells. Aminooxyacetic acid (AOA), an inhibitor of 1-aminocyclopropane-1-carboxylicacid synthase, inhibited the production of ethylene and raisedlevels of spermidine by increasing the availability of S-adenosylmethionine(SAM) for the synthesis of polyamines. In contrast, methylglyoxalbis (guanylhydrazone) (MGBG), an inhibitor of S-adenosylmethioninedecarboxylase (SAMDC), an enzyme involved in the biosynthesisof polyamines, caused a slight increase in the rate of biosynthesisof ethylene. However MGBG did not decrease the rate of biosynthesisof polyamines in 10-day-old senescing cells. Although MGBG inhibitedthe conversion of L-[U-^l4C]methionine into labeled spermidinevia SAM both in 4-day-and in 10-day-cultured cells, it stimulatedthe conversion of L-[U-^l4C]aspartic acid into labeled spermidinein 10-day-cultured cells. In actively dividing 4-day-culturedcells, L-[U-¹⁴C]homo-serine was also converted into polyamines.In senescing cells, which produce large amounts of ethylene,the biosynthesis of spermidine from aspartic acid coincidedwith that from methionine. In actively growing cells, whichproduce large amounts of polyamines, the biosynthesis of spermidinefrom homoserine coincided with that from methionine. These resultsindicate that homoserine and aspartic acid can be both usedas precursors in the biosynthesis of polyamines and help tomaintain appropriate titers of polyamines, when SAMDC is inhibitedand the level of decarboxylated SAM becomes limiting. (Received May 14, 1990; Accepted March 11, 1991)     

Acyl Lipid Metabolism in Germinating Hazel Seeds (Corylus avellana L.)

A decreasing percentage of radioactivity from [U-¹⁴C]-oleateand [U-¹⁴C]-palmitate was recovered in the lipid fractions ofgerminating hazel cotyledons. The pattern of incorporation ofthe acids into the cotyledon glycerides was consistent withtheir degree of saturation. The relative incorporation intothe cotyledon phospholipids changed during germination. Radioactivityfrom both acids was recovered in increasingly unsaturated fattyacids in the cotyledon hpids. Diversion of both [U-¹⁴C]-fatty acids into acyl lipid synthesisoccurred in the germinating embryonic axes. Both were increasinglyrecovered in mixed glyceride groups which contained diglyceridesand highly unsaturated triglycerides. The two acids gave differentpatterns of incorporation in the axis phospholipids. Desaturationof the acids occurred to a lesser extent than in the germinatingcotyledons.     

Intramuscular fatty acid metabolism evaluated with stable isotopic tracers

We evaluated the applicability of stableisotopic tracers to the study of intramuscular fatty acid metabolism byinfusing both[U-¹³C]palmitateand [1-¹³C]oleateintravenously for 4 h into fasted conscious rats. Skeletal muscles weresequentially biopsied, and the concentration and ¹³C enrichment of fatty acids weremeasured by gas chromatography/combustion/isotope ratio massspectrometry. Throughout the study, the¹³C enrichment of plasma palmitateand oleate remained substantially greater than intramuscularnonesterified palmitate and oleate enrichment, which in turn wasgreater than intramuscular triglyceride palmitate and oleateenrichment. Fractional synthesis rates of intramuscular triglyceridesin gastrocnemius and soleus were 0.267 ± 0.075 and 0.100 ± 0.030/h (P = 0.04), respectively, asdetermined by using[U-¹³C]palmitate, andwere 0.278 ± 0.049 and 0.075 ± 0.013/h(P = 0.02), respectively, by using[1-¹³C]oleate. Weconclude that plasma free fatty acids are a source for intramusculartriglycerides and nonesterified fatty acids; the latter are likely thesynthetic precursors of the former. Uniformly and singly labeled[¹³C]fatty acidtracers will provide an important tool to study intramuscular fattyacid and triglyceride metabolism.

     

ERRATA

Page 678, line 3, for [4-¹⁴C] read [I-¹⁴C] Page 678, line 4, for [I-¹⁴C] read [4-¹⁴C] Page 679, line 17, for C-I of malate read C-4 of malate Page 679, line 18, for C-4 of malate read C-I of malate     

Metabolic Alterations Associated With Abscisic Acid-Induced Frost Hardiness in Bromegrass Suspension Culture Cells

Metabolic alterations associated with the induction of freezingtolerance by abscisic acid (ABA) were characterized by chemicalanalysis and by [U-^l4C]sucrose partitioning into cellular constituentsin bromegrass (Bromus inermis Leyss cv. Manchar) cell suspensioncultures. ABA caused a significant elevation in dry matter,particularly in the fraction insoluble in 85% ethanol, thatwas highly correlated with enhanced frost tolerance. Cell walls,the largest component of the insoluble fraction, increased significantlyas frost tolerance increased throughout the ABA treatment period.ABA stimulated total [¹⁴C]sucrose uptake by cells from 7% onday 1 to 97% on day 7 compared to control cells. Partitioningstudies detected a significant increase in ¹⁴CO₂ evolution at3, 5 and 7 days after ABA treatment and a significantly higherincorporation of [¹⁴C]sucrose into the ethanol insoluble fractionafter 5 and 7 days of treatment. Organic acid depletion in ABA-treatedcells was also highly correlated with the increase in hardiness.The concentration of total sugars was higher in ABA-treatedcells. The results indicate that most of the metabolic changesduring ABA-induced acclimation were similar to changes reportedfor cells acclimated in response to low temperature. ¹Oregon Agricultural Experiment Station Technical Paper No.9052 ²Present address: Department of Horticulture, University ofSaskatchewan, Saskatoon, Sask. Canada S7N 0W0 (Received November 1, 1989; Accepted March 13, 1990)     

Chloroplast Development in 4-Thiouridine-Cultured Radish Seedlings VI. Anabolic Pathway of 4-Thiouridine

In germinating radish seeds, [U-¹⁴C]-4-thiouridine was convertedto 4-thio-UMP, 4-thio-UDP, 4-thio-UTP, 4-thio-UDP glucose and4-thiouracil, of which 4-thiouracil accounted for 60–85%.4-Thio-UTP is incorporated into RNAs of radish seedlings [Shibataet al. (1980) FEBS Lett. 119: 85]. These same metabolites werelabeled following germination of radish seeds with [2-¹⁴C]-4-thiouracil.4-Thiouridine was hydrolyzed by the uridine nucleosidase (EC3.2.2.3 [EC] ) of radish seedlings as effectively as was uridine.The activity of uridine nucleosidase was increased by germinationwith 4-thiouridine. These results are a strong indication that4-thiouridine is converted to 4-thiouracil, then to 4-thio-UMPby uracil phosphoribosyltransferase (EC 2.4.2.9 [EC] ). The alternativeformation of 4-thio-UMP from 4-thiouridine by uridine kinase(EC 2.7.1.48 [EC] ) also was suggested. A possible mechanism whichmay cause inhibition of chloroplast biogenesis in 4-thiouridine-culturedseedlings is discussed. (Received October 12, 1981; Accepted January 14, 1982)     

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     

N-Acetylglucosamine Transfer Reactions and Glycoprotein Biosynthesis in Castor Bean Endosperm

N-Acetyl-[³H]glucosamine supplied to intact 3 d old castor beanendosperm tissue was incorporated into TCA-insoluble productpresumed to be glycoprotein. After an incubation time of 2 hthe major paniculate location of this product within the cellwas the endoplasmic reticulum. Cell-free preparations containingparticulate enzymes transferred N-acetyl-[¹⁴C]glucosamine fromUDP-N-acetyl-[¹⁴C]glucosamine into a fraction soluble in chloroform/methanol(2: 1, by vol), a fraction soluble in chloroform/methanol/water(10: 10: 3, by vol.), and an insoluble residue. Mild acid hydrolysisreleased the saccharide moieties from the lipids. Paper chromatographicanalysis of the released saccharides established that the C/M-solubleproducts contained both N-acetyl-[¹⁴C]glucosamine and N, N'-diacetyl-[¹⁴C]chitobiose.In contrast, N-acetyl-[¹⁴C]glucosamine released from the C/M/W-solubleproduct was contained in an oligosaccharide, probably in associationwith unlabelled mannose residues. The stimulatory effect ofdolichol monophosphate and the inhibitory effect of tunicamycinon saccharide-lipid synthesis indicated that N-acetyl-glucosamineis transferred to a glycopolymer by the established reactionsof the dolichol monophosphate pathway. The enzymes catalysingthe constituent reactions of this pathway were exclusively locatedin the ER.     

The Resolution by HPLC of RS-[2-14C]Me 1', 4'-cis-Diol of Abscisic acid and the Metabolism of (-)-R- and (+)-S-Abscisic Acid

The R- and S-enantiomers of racemic [2-¹⁴C]Me 1', 4'-cis-diolof abscisic acid have been separated by high performance liquidchromatography on an optically-active Pirkle column. R-[2-¹⁴C]-and S-[2-¹⁴C]abscisic acids, formed from the Me 1', 4'-cis-diolby oxidation and alkyline hydrolysis were fed to tomato shootsand the extracts analysed by reversed phase high performanceliquid chromatography. R-[2-¹⁴C]abscisic acid formed mainlythe abscisic acid glucose ester (ABAGE), abscisic acid l'-glucoside(ABAGS) and an uncharacterized conjugate. Dihydrophaseic acid4'-B-D-glucoside, the major metabolite of RS-abscisic acid intomato shoots, was found to be derived virtually exclusivelyfrom the natural, S-abscisic acid. Phaseic acid and conjugatesof abscisic acid were also found as products of the naturallyoccurring enantiomer. The resolution method was used to measurethe relative proportions of R and S enantiomers in the freeacid liberated from conjugates formed from RS-[2-¹⁴C]ABA fedto shoots. The ratios show an excess of the R-enantiomer: 5.8:1, ABAGE; 29.4: 1, ABAGE; 8.3: 1 for an uncharacterized conjugateand 6.1: 1 for the residual free [2-¹⁴C]ABA. Key words: ABA, HPLC, Tomato     

Unsaponifiable Lipid Biosynthesis in the Seedling of Euphorbia lathyris L.: A Bypass via Alcoholic Fermentation

[1-¹⁴C]-ethanol supplied to the cotyledons of 9-d-old Euphorbialathyris seedlings was rapidly incorporated into unsaponifiablelipids, particularly into sterols, latex triterpenols and intothe triterpene ketones of the epicuticular wax. The [¹⁴C]-triterpenoidproduction from ethanol was hardly affected by sucrose in theexternal medium when sucrose uptake rates were low, but whenthe uptake rate was higher the [¹⁴C]-triterpenoid productionfrom [¹⁴C]-ethanol was greatly reduced. This observation isconsistent with the proposition that at high sucrose uptakerates, some sucrose is converted into ethanol, so that the incorporationof [¹⁴C]-ethanol into triterpenoids is reduced by competitionwith endogenously formed ethanol. A calculation based on theputative daily ethanol production in the cotyledons and thedaily triterpenoid production of seedlings indicates that about10 % of the triterpenoid synthesis in vivo may be from ethanol. Ethanol, Euphorbia lathyris, fermentation, seedling, triterpenoid biosynthesis