Localization of absorbed aluminium in pea root and its binding to nucleic acids

Aluminium (Al³⁺) considerably inhibited the root elongationof Alaska pea at concentrations higher than 10^–4 M andpH 4.5. The absorbed Al³⁺ in roots was localized in the epidermisand regions where cells actively divided, such as root tip anddifferentiating lateral root. In cells, Al³⁺ accumulated mainlyin the nuclei and walls. Al³⁺ in nucleic acids increased upto 24 hr after treatment with 10^–3M AlCl₃, and did notdecrease markedly after transfer of 10-hr treated plants towater. Molecular sieving chromatography showed that Al³⁺ innucleic acids associated preferentially with DNA. However, invitro association of Al³⁺ with DNA and RNA was nearly the same.When Al³⁺ and nucleic acid were mixed in vitro, the moleculesof Al³⁺ being adjusted to be equal to those of phosphorus innucleic acid, only 25% of the Al³⁺ associated with nucleic acid.The presence of NaCl up to 0.4 M and MgCl₂ up to 0.05 M increasedthe association of Al³⁺ with DNA. When the phosphorus in DNAwas masked by histone, the association of Al³⁺ with DNA wasconsiderably reduced. (Received September 29, 1975; )     

The influence of salinity on the utilization of root anaplerotic carbon and nitrogen metabolism in tomato seedlings

In hydroponically grown Lycopersicon esculentum (L.) Mill. cv.F144 the site of NO₃^– reduction and assimilation withinthe plant was shifted from the shoot to the root by salinity.Uptake of NO₃^– from the root solution was strongly inhibitedby salinization. Consequently, NO₃^– concentrations inthe leaf, stem and root tissues as well as the nitrate reductaseactivities of the leaves were lower in salinized than in controlplants. Lower NO₃^–, but higher reduced-N, concentrationswere observed in the xylem sap as a result of the enhanced participationof the root in NO₃^– reduction in salinized plants. Lowerstem K⁺ concentrations and leaf malate concentrations were foundin salinized compared to control plants which indicates reducedfunctioning of the K⁺–shuttle in the salinized plants. Incorporation of inorganic carbon by the root was determinedby supplying a pulse of NaH¹⁴CO₃ followed by extraction andseparation of the labelled products on ion exchange resins.The rate of H¹⁴CO₃^– incorporation was c. 2-fold higherin control than in salinized plants. In salinized plants theproducts of H¹⁴CO₃^– incorporation within the roots werediverted into amino acids, while the control plants divertedrelatively more ¹⁴C into organic acids. Products of inorganiccarbon incorporation in the roots of salinized plants providean anaplerotic source of carbon for assimilation of reducedNO₃^– into amino acids, while in control plants the productswere predominantly organic acids as part of mechanisms to maintainionic balance in the cells and in the xylem sap. Key words: Tomato, nitrate, PEPc, respiration, salinity     

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     

Time sequence of the effect of ethylene on transport, uptake and decarboxylation of auxin

The effect of ethylene on the uptake, decarboxylation and basipetaltransport of IAA-1-¹⁴C, IAA-2-¹⁴C and NAA-1-¹⁴C in cotton stemsections (Gossypium hirsutum L., var. Stoneville 213) was studied.A reduction in the capacity of cotton stem sections to transportauxin basipetally appears in sections excised from plants exposedto ethylene for only 3 hr and increases with fumigation time. In addition to reducing transport, increasing ethylene pretreatmentperiods from 3 to 15 hr also progressively reduced the uptakeof ¹⁴C and increased the release of ¹⁴C as ¹⁴CO₂ from IAA-1-¹⁴C.The effect of ethylene on the decarboxylation of IAA-1-¹⁴C wassignificant when expressed as either the cpm of ¹⁴C releasedper hr per mg dry weight or the cpm released per hr per mm²in contact with the IAA donor. Comparative experiments usingIAA-1-¹⁴C and IAA-2-¹⁴C demonstrated that the effect of ethyleneon the decarboxylation of IAA was primarily a cut surface effectwhich apparently contributes to the reduction of IAA uptakeby ethylene. Although ethylene significantly reduced the transport of NAA-1-¹⁴C,uptake was significantly increased rather than decreased aswith IAA-1-¹⁴C while decarboxylation was unaffected. Ethylene pretreatment caused no significant changes in the dryweight or the cross-sectional area of the absorbing surfaceof the transport tissue. ¹A contribution of the Texas Agricultural Experiment Station.Supported in part by Grant GB-5640, National Science Foundationand grants from the Cotton Producers Institute and the NationalCotton Council of America. ²Present address: Central Research Department, E. I. Du PontDe Nemours and Company, Wilmington, Delaware 19898, U. S. A. (Received May 29, 1969; )     

Dynamics of Carbon Photosynthetically Assimilated in Nodulated Soya Bean Plants under Steady-state Conditions 2. The Incorporation of 13C into Carbohydrates, Organic Acids, Amino Acids and some Storage Compounds

Nodulated soya bean (Glycine max L.) plants at the early floweringstage were allowed to assimilate ¹³CO₂ under steady-state conditions,with a constant ¹³C abundance, for 8 h in the light. The plantswere either harvested immediately or 2 d after the end of the¹³CO₂ feeding, divided into young leaves (including flower buds),mature leaves, stems+petioles, roots and nodules; the ¹³C abundancein soluble carbohydrates, organic acids, amino acids, starchand poly-ß-hydroxybutyric acid was determined witha gas chromatography-mass spectrometry. The rapid turnover of ¹³C in the sucrose pools observed in allorgans of the plants showed that sucrose was the principal materialin the translocation stream of primary products of photosynthesis.At the end of the ¹³CO₂ exposure, sucrose in the mature leavesas the major source organs and in the stems+petioles was labelledwith currently assimilated carbon to about 75 per cent, whereasa much higher labelling of sucrose was found in the roots andin the nodules. This suggests the existence of two or more compartmentedpools of sucrose in mature leaves and also in stems+petioles. The relative labelling patterns of individual organic acidsand amino acids were similar in various plant organs. However,the rapid turnover of succinate and glycine was characteristicof nodules. Treatment with a high concentration of nitrate inthe nutrient media increased the turnover rate of amino acidcarbon in shoot organs and roots, while it markedly decreasedthe labelling of amino acids in nodules. The cyclitols, exceptfor D-pinitol, were significantly labelled with assimilated¹³C in mature leaves, but in nodules, the labelling was verymuch less. In the nodules, which were actively fixing atmospheric nitrogen,a large proportion (80–90 per cent) of currently assimilatedcarbon was found as sucrose and starch at the end of the ¹³CO₂feeding. This was also true of the roots. On the other hand,in young growing leaves, the distribution of currently assimilatedcarbon into sucrose, starch and other soluble compounds wasmuch less. This suggests that a large amount of carbon assimilatedby and translocated to young leaves was used to make up structuralmaterials, mainly protein and cell wall polymers synthesis,during the light period. Glycine max L., soya bean, ¹³CO₂ assimilation, carbon metabolism in nodules     

The Distribution of 14C-labelled Assimilates in Young Apple Trees as Influenced by Doses of Supplementary Nitrogen: II. Soluble Carbohydrates and Amino Acids

Methanol extracts of young MM.104 apple trees fed ¹⁴CO₂ viaa single leaf were fractionated to compare ¹⁴C activity in totalsoluble sugar and amino acid components. ¹⁴C activity in aminoacids increased after the supply of ammonium nitrate to thesoil in plants where ¹⁴C labelled carbohydrates were presentin the roots. Estimates of specific carbon activity gave lowervalues for the amino acid carbon than the general value fortotal soluble carbohydrates. The fractionation of subsequentmethanol extracts of MM.104 roots has shown that sucrose hadlower specific activity than other components. Although thelevels of activity would accord with sucrose being a substratefor amino acid synthesis, an alternative explanation for theobserved results involving a cyclical system for transferringnitrogen is postulated.     

CO2 Assimilation and Partitioning of Carbon in Maize Plants Deprived of Orthophosphate

In order to study the effects of inorganic phosphate (P1) starvationon C₄plants, 3-week-old maize plants (Zea maysL cv. Brulouis)were grown in a growth chamber on a nutrient solution withoutP1 over 22 d During the first 2 weeks, Pi-starved plants grewas well as control plants The Pi concentration in the planttissue decreased rapidly with time, which suggests that normalbiomass production can be maintained at the expense of internalP1 In addition, photosynthetic CO2 assimilation measured 4-6h after dawn was not affected, but the concentration of glucose,sucrose, and starch in leaves was much higher than in the controls¹⁴CO₂ pulse-chase experiments earned out on the ninth day oftreatment showed that ¹⁴CO₂ assimilation was perturbed duringthis initial period, resulting in a larger flow of carbon toboth starch and sucrose At the beginning of the third week ofP1 starvation (15 d after treatment) ¹⁴C incorporation intosucrose stayed high relative to controls but this was not thecase for starch At the end of the third week of P1-deficiency,shoot growth was considerably reduced and fresh weight was onlyone-third of that of the control plants. The P1 concentrationof both the leaf and root tissues was less than 1.0 µmolg^–1 FW compared to 20-25µmol g¹ FW in the controls.Photosynthetic CO₂ assimilation was reduced and the leaf concentrationof sucrose and starch, which had begun to decrease after theend of the second week of P1 limitation, became lower than inthe controls. These results obtained on maize plants show thatphotosynthesis and carbon partitioning between sucrose and starchwere strongly affected by P1 deficiency, similar to C₃ species. Key words: CO₂ assimilation, corn, orthophosphate deficiency, starch, sucrose     

Essential oils enhanced by ultra-high carbon dioxide levels from Lamiaceae species grown in vitro and in vivo

The growth (fresh weight), morphogenesis (leaves, roots and shoots) and essential oil composition of mint (Mentha sp. L.) and thyme (Thymus vulgaris L.) plants were determined after 8 weeks under 350, 1,500, 3,000, 10,000 and 30,000 µmol mol^-1 CO₂. Plants were grown in vitro on basal medium (BM) consisting of Murashige and Skoog salts and 0.8% agar that contained either 0 or 3% sucrose under a 16-h (day)/8-h (night) photoperiod at a light intensity of 180 µmol s^-1 m^-2 or in soil in a greenhouse under conditions of natural sunlight. Ultra-high CO₂ levels (i.e. ́,000 µmol mol^-1 CO₂) substantially increased fresh weights, leaves, shoots and roots for all plants compared to plants grown under ambient air (350 µmol mol^-1 CO₂) both in vivo and in vitro. For both species, 10,000 µmol mol^-1 CO₂ was the optimum concentration to obtain the largest growth and morphogenesis responses under in vitro conditions, while the 3,000- to 10,000-µmol mol^-1 CO₂ range provided the largest yields for soil-grown plants. Essential oil composition (i.e. monoterpenes, piperitonone oxide and limonene from mint and aromatic phenol and thymol from thyme) from the shoot portion of plants grown at all CO₂ levels was analyzed in CH₂Cl₂ extracts via gas chromatography. Higher levels of secondary compounds occurred in vitro when cultures were grown under ultra-high CO₂ levels than in ambient air. The concentration of thymol, a major secondary compound in thyme plants grown on BM containing sucrose, was 317-fold higher at 10,000 µmol mol^-1 CO₂ than in plants grown under ambient air conditions with the same BM. The levels of secondary compound in in-vitro-grown plantlets exposed to ultra-high CO₂ concentrations exceeded those occurring in plants grown in the greenhouse under the same CO₂ levels. Substantially higher levels of secondary compound occurred in plants under ultra-high CO₂ levels on BM containing sucrose than on BM lacking sucrose or in soil. Thymol levels in thyme plants grown on BM containing sucrose were 3.9-fold higher at 10,000 µmol mol^-1 CO₂ than in shoots grown on BM without sucrose under the same CO₂ levels. High positive correlations occurred between thymol concentrations and CO₂ levels, fresh weights, shoots, roots and leaves when thyme shoots were grown on BM with sucrose. High positive correlations for thyme shoots grown on BM without sucrose only occurred between thymol concentrations and CO₂ levels, fresh weights, shoots and leaves. No positive correlations between thymol concentrations and CO₂ levels or any growth or morphogenesis responses occurred for thyme shoots when grown in soil.     

Dynamics of Carbon Photosynthetically Assimilated in Nodulated Soya Bean Plants under Steady-state Conditions 3. Time-course Study on 13C Incorporation into Soluble Metabolites and Respiratory Evolution of 13CO2 from Roots and Nodules

Well-nodulated soya bean (Glycine max L.) plants were allowedto assimilate ¹³CO₂ for 10 h in the light, under steady-stateconditions in which CO₂ concentration and ¹³C abundance wereboth strictly controlled at constant levels. The respiratoryevolution of ¹³CO₂ from roots and nodules and ¹³C incorporationinto various metabolic fractions were measured during the ¹³CO₂feeding and subsequent 48 h chase period. CO₂ respired from nodules was much more rapidly labelled with¹³C than that from roots. The level of labelling (percentageof carbon currently assimilated during the ¹³COM₂ feeding period)of CO₂ respired from nodules reached a maximum of about 87 percent after 4 h of steady-state ^l3CO₂ assimilation and thereafterremained fairly constant. The absolute amount of labelled carbonevolved by the respiration of the nodules during the 10 h ¹³CO₂feeding period was 1·5-fold that of root respiration.These results demonstrated that the currently assimilated (labelled)carbon was preferentially used to support nodule respiration,while root respiration relied considerably on earlier (non-labelled)carbon reserved in the roots. Sucrose pools were mostly composed of currently assimilatedcarbon in all tissues of the plants, since the levels of labellingaccounted for 86–91 per cent at the end of the ¹³CO₂ feeding.In the nodules, the kinetics and levels of sucrose labellingwere in fairly good agreement with those of respired CO₂, whilein the roots, the level of labelling of respired CO₂ was significantlylower than that of sucrose. Succinate and malate were highly labelled in both roots andnodules but they were labelled much more slowly than sucroseand respired CO₂. The kinetics and levels of labelling of theseKrebs cycle intermediates resembled those of major amino acidswhich are derived directly from Krebs cycle intermediates. Itis suggested that large fractions of organic acids in noduleswere physically separate from the respiration site. Glycine max L., Soya bean, ¹³CO₂ assimilation, respiratory evolution of ¹³CO₂, carbon metabolism in root nodules     

The Growth and Physiology of Pinus strobus L. Seedlings as Affected by Various Nutritional Levels of Nitrogen and Phosphorus

Potted white pine (Pinus strobus L.) seedlings were grown ingravel either in outdoor cold frames or in growth chambers.They were watered every second day with a salt solution containingdifferent amounts of nitrogen and phosphorus. After 13 weeksof growth individual seedlings were illuminated separately for8 h in the presence of ¹⁴CO₂ and the rates of their apparentphotosynthesis, respiration, and translocation of recent ¹⁴C-photosynthateto their roots were observed. Roots were extracted with 80 percent ethanol and the nature of various ¹⁴C compounds in theextract was determined by paper chromatography. The best over-all growth of plants, mycorrhizal development,apparent photosynthesis, and translocation of recent photosynthateto the roots were observed in plants grown at the intermediatelevels of N and P nutrition. Sucrose was always the dominant form in which recently translocated¹⁴C occurred in the roots, although with increased nitrogensupply there was increased hydrolysis of sucrose to hexosesand appearance of ¹⁴C in the amino- and organic acids.     

Gibberellic-Acid-Promoted Transport of Assimilates in Stems of Phaseolus vulgaris. Effects on Assimilate Accumulation by the Sink

Under conditions of apoplastic unloading from the sieve element-companioncell (se-cc) complexes in fully-elongated stems of Phaseolusvulgaris plants, gjbberellic acid (GA₃ stimulated in vitro uptakeof [¹⁴C]sucrose by the stem tissues. The GA₃, response dependedupon the incubate containing calcium ions and being bufferedat pH 6. The GA₃ action could be accounted for by a reductionin the Michaelis-Menten constant of the uptake process. Promotedtransport by GA₃ in the decapitated stems resulted in all thetissues accumulating higher levels of [¹⁴C]photosynthates. Comparisonof this response with that for in vitro uptake of [¹⁴C]sucroseindicated that GA₃ stimulation of the sucrose uptake processcontributed significantly to the accumulation of photosynthatesby the pith alone. The bulk of enhanced photosynthate accumulationby the remaining stem tissues can be accounted for by a GA,-inducedelevation of the apoplast sucrose concentration. In terms ofonset and change in rate, the time-course kinetics of GA₃ stimulationof [¹⁴C]photosynthate transport and of in vitro [¹⁴CJsucroseuptake were found to be similar. It is proposed that GA₃ promotionof photosynthate accumulation by the pith tissues is a minorcontributing factor to GA₃ regulation of phloem translocation Phaseolus vulgaris L., french bean, stem, assimilate transport, gibberellic acid, rink accumulation     

Carbon Loss from the Roots of Forage Rape (Brassica napus L.) Seedlings Following Pulse-labelling with 14CO2

The loss of organic material from the roots of forage rape (Brassicanapus L.,) was studied by pulse-labelling 25-d-old non-sterilesand-grown plants with ¹⁴CO₂. The distribution of ¹⁴C withinthe plant was measured at 0, 6 and 13 d after labelling whilst¹⁴ C accumulating in the root-zone was measured at more frequentintervals. The rates of ¹⁴C release into the rhizosphere, andloss of ¹⁴CO₂ from the rhizosphere were also determined. Thesedata were used to estimate the accumulative loss of ¹⁴C fromroots and loss respiratory ¹⁴CO₂ from both roots and associatedmicro-organisms. Approximately 17-19% of fixed ¹⁴CO₂ was translocatedto the roots over 2 weeks, of which 30-34% was released intothe rhizosphere, and 23-24% was respired by the roots as ¹⁴CO₂. Of the ¹⁴C released into the rhizosphere, between 35-51%was assimilated and respired by rhizosphere micro-organisms.Copyright1993, 1999 Academic Press Brassica napus L., carbon loss, carbon partitioning, microbial nutrition, microbial respiration, forage rape, pulse-labelling, rhizodeposition, root respiration, sand culture     

Specific Increase in Phosphatase Isozymes in Cucumber Roots Caused by Calcium Deficiency

Phosphatases in cucumber roots, whose production was inducedby Ca^2$ deficiency, were characterized chromatographically usingATP, 2'(3')-AMP and p-nitrophenyl-phosphate (PNPP) as substrates.Ca^2$ deficiency stimulated greater than 10-fold increases inthe activities with these substrates of the non-adsorbed fractionfrom a DEAE-cellulose column. Several fractions associated withthese phosphatase activities were eluted from the column withNaCl solution; their levels increased less with Ca^2$ starvation.When the non-adsorbed fraction from Ca^2$-straved roots was appliedto a Sephadex G-200 column, fractions associated with 2'(3')-AMPase(phosphatase I) and with both ATPase and PNPPase (phosphataseII) were separated. In the control roots, very weak activitiesof phosphatases I and II were observed at the same positionon the gel filtration. The phosphatase I isolated from boththe control and Ca^2$-starved roots was extremely specific tonucleoside 2'(3')-monophosphates, whereas phosphatase II fromboth types of roots had a relatively broad substrate specificity.When phosphatase I from Ca^2$-starved roots was stained with2'(3')-AMP in CaCl₂ after polyacrylamide gel electrophoresis,a single band was obtained. Phosphatase I from control rootsalso showed a single band, with the same Rf value. PhosphataseII from both types of roots contained two isozyme bands whenthe activities were stained with either ATP or PNPP. These resultsindicate that Ca^2$ starvation causes specific increases in thelevel of phosphatases I and II in cucumber roots. (Received October 28, 1981; Accepted January 19, 1982)     

Root Development and Source-Sink Relations in Carrot, Daucus carota L: II. EFFECTS OF ROOT PRUNING ON CARBON ASSIMILATION AND THE PARTITIONING OF ASSIMILATES

Physiological responses to root pruning were investigated bycomparing ¹⁴CO₂ fixation rates, the partitioning of ¹⁴C-labelledassimilate, and soluble and insoluble carbohydrate levels inthe leaves of carrot plants following the removal of some ofthe fibrous roots, or fibrous roots and part of the tap root.Root pruning reduced ¹⁴CO₂ fixation by 28–45% but leafspecific activity (¹⁴C assimilation g-¹ leaf fresh weight) wasunchanged. The proportion of total assimilate exported to theroot system increased following root pruning and this was atthe expense of the developing leaves. In younger plants (wherethe tap root received 10% of the assimilate) the supply of ¹⁴Cto the tap root was maintained in spite of root pruning. However,shortening the tap root to 3 cm in older plants (in which 30%of the fixed 14C was normally exported to the developing storageorgan), reduced its sink capacity and resulted in slightly greaterretention of ¹⁴C in the mature leaves. Greater concentrationsof insoluble carbohydrate were found in the mature leaves followingroot pruning but soluble sugar content was unaffected. Onlysmall differences were observed in the distribution of ¹⁴C betweensoluble and insoluble carbohydrate fractions when plants werefed ¹⁴CO₂ several days after the root pruning operations. Thesephysiological responses were mainly associated with the removalof fibrous roots and support the view that the fibrous rootsystem is more important than the developing storage organ inregulating growth in young carrot plants.     

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 effect of salinity on glucose absorption and incorporation by pea roots

Osmotic adaptation was observed in pea plants grown in Na₂SO₄salinized media but no complete adaptation was observed in plantsgrown in NaCl salinized media. The absorption of externally supplied glucose was depressedin pea root tips from plants grown in media salinized with eitherNaCl or Na₂SO₄. Under NaCl salinity this depression increasedwith increasing salinity. Under Na₂SO₄ salinity, no significantinhibition of absorption was observed in roots exposed to waterpotentials higher than –5 atmosphere. The amount of ¹⁴Creleased as CO₂, expressed as the percent of absorbed ¹⁴C, increasedwith increasing salinity of both types. In roots grown underNaCl salinity, the incorporation of ¹⁴C into ethanol non-soluble,acid hydrolyzable substances was markedly inhibited. This inhibitionwas increased by increasing the external salinity. The effectof Na₂SO₄ salinity was similar but not so pronounced. The incorporation of ¹⁴C from externally supplied glucose intothe alkali-soluble fraction was practically uneffected by salinity.Non-extractable ¹⁴C was decreased in roots exposed to NaCl butwas not, apparently, effected by Na₂SO₄). Because of the smallnessof this fraction no clear cut conclusion can be made. Possiblemechanisms for the events are discussed. (Received October 26, 1972; )     

Source--sink Relationships and Carbon Metabolism in Tomato Leaves 1. 14C Assimilate Compartmentation

Effects of the interaction between assimilate availability andsink demand on the metabolism of ¹⁴C assimilates in tomato leaveshave been examined in plants where the source—sink relationshipof assimilates was simplified to one leaf and one fruit truss. During experimentation the source leaf was exposed to either80 or 20 W m^–2 (PAR), while the truss was either retainedor removed. Under these four source-sink conditions, a timecourse study was made on ¹⁴C assimilate distribution in thesource leaf over a period of 23 h after pulse feeding with ¹⁴CO₂. While truss removal caused a temporary increase of ¹⁴C sucrosein leaves under both irradiances, the principal assimilatesaccumulated were starch and hexoses. Decreased ¹⁴C export followingtruss removal was observed within a day in well-illuminatedleaves but after 3 days in leaves under low light. The accumulationof ¹⁴C sucrose at the end of the light period was affected bytruss removal in high light leaves only 3 days later. These observations suggest that while the compartmentation ofnewly fixed assimilate was affected rapidly by the change ofsource—sink relationship, carbon export, as measured by¹⁴C loss, was affected only gradually. The possible effect of sucrose accumulation on photosynthesisis discussed.     

Changes in the Morphology of Roots and Leaves of Carob Seedlings Induced by Nitrogen Source and Atmospheric Carbon Dioxide

Carob seedlings were grown hydroponically for 9 weeks under360 and 800 µl l^-1CO₂. One of two nitrogen sources, nitrateor ammonium, was added to the nutrient medium at concentrationsof 3 mol m^-3. Root systems of the developing plants suppliedwith nitrate compared to those supplied with ammonium were characterizedby:(a)more biomass on the lower part of the root;(b)fewer lateralroots of first and second order;(c)longer roots;(d)higher specificroot length;(e)a smaller root diameter. The morphology of theroot systems of nitrate-fed plants changed in the presence ofelevated carbon dioxide concentrations, resembling, more closely,that of ammonium-fed plants. Total leaf area was higher in ammonium-than in nitrate-fed plants. Nitrate-fed plants had greater totalleaf area in the presence of high carbon dioxide than in normalCO₂, due to an increase in epidermal cell size that led to developmentof larger leaflets with lower stomatal frequency. The observedchanges in the morphology of roots and shoots agreed with theresults observed for total biomass production. Nitrate-fed plantsincreased their biomass production by 100% in the presence ofelevated CO₂compared to 15% in ammonium-fed plants, indicatingthat the response of carob to high CO₂concentrations is verydependent on the nitrogen source. Under elevated CO₂, nitrate-grownplants had a larger content of sucrose in both roots and shoots,while no significant difference was observed in the contentof sucrose in ammonium-grown plants, whether in ambient or enrichedcarbon dioxide. Hence, the differences in soluble carbohydratecontents can, at least partly, account for differences in rootand shoot morphology.Copyright 1997 Annals of Botany Company Ceratonia siliquaL.; carob; ammonium; carbohydrate; carbon dioxide; nitrate; morphology; sucrose     

14CO2 Pulse-Chase Labelling in Clusia minor L.

Conditions and maintenance of growth were chosen so that plantsof Clusia minor L. were obtained which showed the C₃- and CAM-modes of CO₂-exchange, respectively. C. minor is known to accumulateconsiderable amounts of citric acid in addition to malic acidduring the dark-phase of CAM. ¹⁴CO₂-pulse-chase experiments were performed with these plants.Patterns of labelling during the pulse and redistribution oflabel during the chase in the C₃-mode were as expected for C₃-photosynthesis.Pulse-labelling in the CAM-mode during the last hour of thelight period, during the first part of the dark period and duringthe last hour of the dark period always led to an almost exclusiveincorporation of label into malate. Redistribution of labelfrom malate after the pulse at the end of the dark period duringthe chase in the subsequent light period followed the patternexpected for light-dependent reassimilation of CO₂ remobilizedfrom malate in CAM during the light period. During the chasesin the dark period, label was transferred from ^l4C-malate tocitrate. This suggests that during accumulation of citric acidin the dark period of CAM in C. minor, citrate is synthesizedin the mitochondria from malate or oxaloacetate after formationof malate via phosphoenolpyruvate carboxylase. The experiment also showed that no labelled compounds are exportedfrom leaves in the CAM-mode during the dark period. In plantsof the C₃-mode the roots proved to be strong sinks. Key words: Clusia minor, labelling, pulse-chase, ¹⁴CO₂     

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