14CO2 Assimilation and 14C-photosynthate Translocation in Different Leaves of Sunflower

Chlorophyll and nitrogen contents were highest in leaves of middle position, similarly as photosynthetic efficiency represented by ¹⁴C fixation (maxima in leaf 5 from the top). All the leaves lost ¹⁴C after 2 weeks of ¹⁴CO₂ exposure. However, the reduction in radioactivity was less in young upper leaves than in the mature lower leaves. Leaves exported ¹⁴C-photosynthates to stem both above and below the exposed leaf. Very little radioactivity was recovered from the seeds of plants in which only first or second leaves were exposed to ¹⁴CO₂ implying thereby that the carbon contribution of first two leaves to seed filling was negligible. The contribution of leaves to seed filling increased with the leaf position up to the sixth leaf from the top and after the seventh leaf their contribution to seed filling declined gradually.     

Turnover of Carbohydrates in Relation to Growth in Apple Trees. II. Distribution of 14C Assimilates Labelled in Autumn, Spring and Summer

One-year-old plants of the apple rootstocks MM. 106 and M.7were allowed to assimilate ¹⁴CO₂ in autumn, spring and summerand the distribution of the tracer within the plant over a growingseason was followed. In MM.106 distribution of the tracer intwo fractions of extractable carbohydrate and the residues representingstructural material, was determined. The results of the radioactivityassay are discussed in relation to seasonal patterns of assimilatesupply and demand in the different regions of the plant. Malus sylvestris L, apple, ¹⁴C assimilates, distribution of carbohydrates     

Influence of Flooding on Net CO2Assimilation, Growth and Stem Anatomy of Annona Species

A series of experiments was conducted to assess net CO₂assimilationand growth responses to waterlogging of grafted and seedlingtrees in the genus Annona. Seedlings of A. glabra, A. muricataandA. squamosa L., and scions of ‘Gefner’ atemoya(A. squamosaxA. cherimola Mill.), ‘49-11’ (‘Gefner’atemoyaxA. reticulata L.), ‘4-5’ (‘Priestley’atemoyaxA. reticulata), A. reticulata grafted onto either A.glabra, A. reticulata orA. squamosa rootstocks were floodedfor up to 60 d. Soil anaerobiosis occurred on the third dayof flooding. Seedlings ofA. glabra and A. muricata, and thescions ‘49-11’, ‘Gefner’ atemoya, andA. reticulata grafted onto A. glabra rootstock were consideredflood tolerant based on their ability to survive and grow inflooded conditions. Scions of the normally flood-sensitive A.reticulata, ‘Gefner’ atemoya, and ‘49-11’tolerated root waterlogging when grafted onto the flood-tolerantspecies, A. glabra. In contrast, flooding of A. squamosa seedlingsand rootstocks, and A. reticulata rootstocks greatly reducedgrowth and net CO₂assimilation rates, and resulted in 20–80%tree mortality. Stem anatomical responses to long-term flooding(12 continuous months) were assessed in seedlings of A. glabraand A. muricata, and trees of ‘49-11’ grafted ontoA. glabra. Flooded trees developed hypertrophied stem lenticels,particularly in A. glabra, and enlarged xylem cells resultingin thicker stems with reduced xylem density. Flooding did notincrease air spaces in pre-existing xylem near the pith or inxylem tissue that was formed during flooding. Thus, flood tolerancedid not involve aerenchyma formation in the stem. Copyright1999 Annals of Botany Company Flood tolerance, net CO₂assimilation, photosynthesis, stem anatomy, shoot growth, anaerobiosis, Annonaceae.     

Xylem Sap Flux Affects Conventional Stem CO2 Efflux Measurements in Tropical Trees

The relationship between sap flux and stem CO₂ efflux was assessed for three mango trees. We observed higher than expected CO₂ effluxes at the place of measurement under intermediate sap flux velocities and lower fluxes under high sap flux velocity. This variation disappeared after removing the tree crown.     

Isotope Labeling and Microautoradiography of Active Heterotrophic Bacteria on the Basis of Assimilation of 14CO2

Most heterotrophic bacteria assimilate CO₂ in various carboxylation reactions during biosynthesis. In this study, assimilation of ¹⁴CO₂ by heterotrophic bacteria was used for isotope labeling of active microorganisms in pure cultures and environmental samples. Labeled cells were visualized by microautoradiography (MAR) combined with fluorescence in situ hybridization (FISH) to obtain simultaneous information about activity and identity. Cultures of Escherichia coli and Pseudomonas putida assimilated sufficient ¹⁴CO₂ during growth on various organic substrates to obtain positive MAR signals. The MAR signals were comparable with the traditional MAR approach based on uptake of ¹⁴C-labeled organic substrates. Experiments with E. coli showed that ¹⁴CO₂ was assimilated during both fermentation and aerobic and anaerobic respiration. The new MAR approach, HetCO₂-MAR, was evaluated by targeting metabolic active filamentous bacteria, including “Candidatus Microthrix parvicella” in activated sludge. “Ca. Microthrix parvicella” was able to take up oleic acid under anaerobic conditions, as shown by the traditional MAR approach with [¹⁴C]oleic acid. However, the new HetCO₂-MAR approach indicated that “Ca. Microthrix parvicella,” did not significantly grow on oleic acid under anaerobic conditions with or without addition of NO₂⁻, whereas the addition of O₂ or NO₃⁻ initiated growth, as indicated by detectable ¹⁴CO₂ assimilation. This is a metabolic feature that has not been described previously for filamentous bacteria. Such information could not have been derived by using the traditional MAR procedure, whereas the new HetCO₂-MAR approach differentiates better between substrate uptake and substrate metabolism that result in growth. The HetCO₂-MAR results were supported by stable isotope analysis of ¹³C-labeled phospholipid fatty acids from activated sludge incubated under aerobic and anaerobic conditions in the presence of ¹³CO₂. In conclusion, the novel HetCO₂-MAR approach expands the possibility for studies of the ecophysiology of uncultivated microorganisms.     

Turnover of Carbohydrates in Relation to Growth in Apple Trees. I. Seasonal Variation of Growth and Carbohydrate Reserves

Growth in young apple trees of the rootstocks MM. 106 and M.7 was estimated by changes in d. wt., and growth in the differentregions of the two rootstocks was compared. Changes in d. wtwere compared with changes in extractable carbohydrates in MM.106 trees. The seasonal variations in d. wt, extractable carbohydratesand residues, are discussed in relation to utilization of reserveand current assimilates in the different regions of plant duringwinter, autumn, spring and summer. Malus sylvestris L, apple, carbohydrate, growth     

Changes in specific radioactivity of sunflower leaf metabolites during photosynthesis in 14CO2 and 12CO2 at three concentrations of CO2

Summary Sunflower (Helianthus annuus L.) leaf discs were exposed to ¹⁴CO₂ or ¹⁴CO₂ followed by ¹²CO₂ at 21% O₂ and three different CO₂ concentrations. After intervals of up to 15 min, the specific activity of some photosynthetic intermediates was determined. At all CO₂ concentrations, the specific activity of 3-phosphoglyceric acid (3-PGA) increased most rapidly and after 15 min of ¹⁴CO₂ feeding was 92% (967 ppm CO₂), 87% (400 ppm CO₂) and 53% (115 ppm CO₂) of CO₂ supplied to the assimilation chamber. The specific activity of glycine, serine and the photorespiratory CO₂ was similar at all CO₂ concentrations, in aggreement with their proposed close metabolic relationship in the glycolate pathway. However, the kinetics of serine and glycine labelling suggested that serine was not totally derived from glycine. Because the specific activity of these glycolate-pathway intermediates was very differnet from that of 3-PGA at all CO₂ concentrations, not all of the carbon traversing this pathway came directly from the Calvin cycle. The non-equilibration of the 3-PGA with the feeding gas reflects the recycling of C from the glycolate pathway into the photosynthetic reduction cycle. Measurements of the rates of CO₂ evolution in the light and estimates of the C flux through the glycolate pathway suggest that the photorespiratory activity was high and similar at 115 ppm CO₂ and 400 ppm CO₂ but inhibited at 967 ppm CO₂.     

Assimilation of 14CO2 by the Inflorescence of Poa annua L. and Lolium perenne L.

The relative assimilatory activity of the inflorescence, itsindividual components, and the leaves of flowering tillers ofPoa annua L. and Lolium perenneL. was determined over the periodfrom inflorescence emergence to seed shedding. The pattern of¹⁴CO₂ fixation was similar for both species and the inflorescencewas by far the most important assimilatory organ of the reproductivetiller, particularly over the latter period of seed developmentas leaf senescence progressed. With the exception of the seedsall parts of the inflorescence showed significant assimilatoryactivity and the lemmas and paleas accounted for 40–50per cent of the total ¹⁴C fixed by the inflorescence in bothspecies. The importance of the grass inflorescence as a photosyntheticstructure is discussed in relation to similar studies on cereals. Poa annua, Lolium perenne, carbon dioxide assimilation, inflorescence     

Effect of High Temperature on Photosynthesis in Beans (II. CO2 Assimilation and Metabolite Contents)

The effect of high temperatures on CO2 assimilation, metabolite content, and capacity for reducing power production in non-photorespiratory conditions has been assessed in two different bean (Phaseolus vulgarus L.) varieties, Blue Lake (commercially available in the United Kingdom) and Barbucho (a noncommercially bred Chilean variety), which are known to differ in their resistance to extreme high temperatures. Barbucho maintains its photosynthetic functions for a longer period of time under extreme heat compared with Blue Lake. The CO2 assimilation rate was increased by increases in temperature, with a decrease in ratio of rates of temperatures differing by 10[deg]C. It is suggested that limitations to CO2 assimilation are caused by metabolic restrictions that can be differentiated between those occurring in the range of 20 to 30[deg]C and 30 to 35[deg]C. It is likely that changes in the capacity for Calvin cycle regeneration and starch synthesis affect photosynthesis in the range of 20 to 30[deg]C. But following an increase in temperature from 30 to 35[deg]C, the supply of reducing power becomes limiting. From analysis of adenylate concentration, transthylakoid energization, and, indirectly, NADPH/NADP+ ratio, it was concluded that the limitation in the assimilatory power was due to an oxidation of the NADPH/NADP+ pool. In the range of 30 to 35[deg]C, the photosystem I quantum yield increased and photosystem II maintained its value. We conclude that the reorganization of thylakoids observed at 30 to 35[deg]C increased the excitation of photosystem I, inducing an increase in cyclic electron transport and a decrease in the supply of NADPH, limiting carbon assimilation.     

Effect of Photorespiratory C2 Acids on CO2 Assimilation,PS II Photochemistry and the Xanthophyll Cycle in Maize

The photorespiration cycle plays an important role in avoiding carbon drainage from the Calvin cycle and in protecting plants from photoinhibition. The role of photorespiration is frequently underestimated in C(4) plants, since these are characterized by low photorespiration rates. The aim of this work was to study the relationship between CO(2) assimilation, PS II photochemistry and the xanthophyll cycle when the photorespiratory cycle is disrupted in Zea mays L. To this end, the photorespiration inhibitor phosphinothricin (PPT) was applied individually or together with the photorespiratory C(2) acids, glycolate and glyoxylate to maize leaves. Application of PPT alone led to the inhibition of CO(2) assimilation. Moreover, feeding with glycolate or glyoxylate enhanced the effect of PPT on CO(2) assimilation. Our results confirm that the avoidance of the accumulation of the photorespiratory metabolites glycolate, glyoxylate or phosphoglycolate, is of vital importance for coordinated functioning between the glycolate pathway and CO(2) assimilation. Relatively early changes in PS II photochemistry also took place when the photorespiratory cycle was interrupted. Thus, fluorescence photochemical quenching (qP) was slightly reduced (10%) due to the application of PPT together with glycolate or glyoxylate. A decrease in the efficiency of excitation-energy capture by open PS II reaction centres (F'v/F'm) and an increase in thermal energy dissipation (non-photochemical quenching, NPQ) were also measured. These observations are consistent with a limitation of activity of the Calvin cycle and a subsequent lower demand for reduction equivalents. The increase in NPQ is discussed on the basis of changes in the xanthophyll cycle in maize, which seem to provide a limited protective role to avoid photoinhibition when the glycolate pathway is blocked. We conclude that C(2) photorespiratory acids can act as physiological regulators between the photorespiratory pathway and the Calvin cycle in maize.     

Effect of Osmotic Stabilizers on 14CO2 Production by Bacteria and Blood

Evolution of (14)CO(2) by whole blood as well as by Diplococcus pneumoniae, Haemophilus sp., Pseudomonas aeruginosa, Pseudomonas diminuta, and Streptococcus pyogenes was examined by using the BACTEC system. The control medium was JLI no. 6A culture vial containing 30 ml of enriched tryptic soy broth and 1.5 muCi of (14)C-substrate. Hypertonic media consisted of control medium with either 1 or 3% NaCl, 10% sucrose, and 5%, 10%, or 15% dextran. The most deleterious treatment to bacteria was 3% NaCl since it not only retarded (14)CO(2) production, but also prevented growth of D. pneumoniae, Haemophilus, and P. diminuta. The 10% sucrose treatment diminished (14)CO(2) output, although it did not retard growth of test organisms. This effect was probably due to (14)C-substrate dilution rather than to osmotic effects. Dextran had slight effect on (14)CO(2) production and slightly acidified the medium. Of the treatments tested, only 10% sucrose reduced normal output of (14)CO(2) by whole blood. This also is probably due to (14)C-substrate dilution. It appears that 10% sucrose is potentially the most useful osmotic agent for radiometric techniques since, although bacterial (14)CO(2) production is lowered, blood (14)CO(2) is lowered also.     

Carbon-14 Distribution in Carbohydrates of Immature Zea mays. Kernels Following CO(2) Treatment of Intact Plants

Shortly after Zea mays L. plants were exposed to ¹⁴CO₂, most of the radioactivity in the kernel occurred in the free monosaccharides, glucose and fructose. Later the proportion of ¹⁴C in sucrose increased and that in the monosaccharides declined. These data have been interpreted as showing that the translocated sugar is hydrolyzed prior to or during its movement into the storage cells of the endosperm. This hydrolysis appears to occur in the “pedicel region” of the kernel. After entry into the endosperm tissue, sucrose was rapidly resynthesized from the monosaccharides prior to its utilization in starch synthesis.     

Photosynthetic Assimilation of 14CO2 by Waterstressed Sunflower Leaves at Two O2 Concentrations and the Specific Activity of Products

Attached leaves of sunflower (Helianthus annuus L. var. Mennonite)with water potentials of –5 to –18 ? 10⁵ Pa, wereexposed for different times to 300 vpm CO₂ containing ¹⁴CO₂and 21 or 1.5% O₂. ¹⁴C accumulated linearly with time in bothO₂ concentrations and at all stresses. 3-Phosphoglyceric acidwas saturated with ¹⁴C after 10 min in unstressed plants atboth O₂ concentrations but with increasing stress the rate ofaccumulation and the specific activity decreased. With decreasingleaf water potential there was accumulation of radioactivityin the glycolate pathway intermediates glycine and serine. Otheramino acids contained a slightly larger proportion of assimilatedcarbon as water potential decreased. The specific activitiesof all compounds were smaller with stress. In contrast to theamino acids less radioactivity accumulated in sugars, organicacids, and sugar phosphates and their specific activities decreasedwith stress. The radioactive labelling patterns and specificactivity measurements are interpreted as showing increased carbonflux in the glycolate pathway and inhibition of the metabolismof serine to sucrose. These changes are related to previousresults showing that with stress photo respiration increasesas a proportion of photosynthesis. Lowering the O₂ concentrationto 1.5% decreased the accumulation of radioactivity in glycineand stopped photorespiration. It increased the amount of radioactivityin serine and sucrose but did not greatly change specific activities.Oxygen effects were independent of water stress. Glycolate pathwaymetabolism is discussed in relation to photorespiration andthe effects of water stress.     

Effect of CO2 Concentration During Growth on a CO2 Concentrating Mechanism in White Clover as Predicted from Differential 14CO2/12CO2Uptake

Lehnherr, B. M?chler, F. and N?sberger, J. 1985. Effect of CO₂concentration during growth on a CO₂ concentrating mechanismin white clover as predicted from differential ¹⁴CO₂/¹²CO² uptake.-J. exp. Bot. 36: 1835-1841. White clover was grown at 20 and100 Pa p(CO₂). The CO₂ response of net photosynthesis and differentialuptake of ¹⁴CO₂ and ¹²CO₂ by leaves were measured at varioustemperatures and at various O₂ and CO₂ partial pressures andcompared with predictions from ribulose bisphosphate carboxylase/oxygenasekinetics. Discrepancies between the observed gas exchange characteristicsfor the leaves and those predicted from the enzyme kineticswere interpreted as being due to a CO₂ concentrating mechanism.Plants grown at 20 Pa p(CO₂) showed a higher affinity for CO₂than plants grown at 100 Pa p(CO₂) when measured at 10 ?C. Nodifference in affinity was found at 30 ?C. The postulated CO₂concentrating effect was greater in plants grown at low CO₂than in plants grown at high CO₂ concentration and occurredonly at low temperature and low CO₂ partial pressure. It issuggested that plants grown at the lower CO₂ partial pressurehave a higher affinity for CO₂ due to a more efficient CO₂ concentratingsystem than plants grown at the higher CO₂ partial pressure. Key words: Photosynthesis, CO₂, concentration, RuBP carboxylase/oxygenase     

Effect of Triacontanol on Chlamydomonas: I. Stimulation of Growth and Photosynthetic CO(2) Assimilation

Treatment of Chlamydomonas reinhardtii cells, cultured at 5% CO₂, with 1 to 1000 micrograms triacontanol (TRIA) per liter resulted in 21 to 35% increases in cell density, 7 to 31% increases in total chlorophyll, and 20 to 100% increases in photosynthetic CO₂ assimilation. The increase in CO₂ fixation with TRIA treatment occurred before, and was independent of, increases in total chlorophyll or cell number. Chlamydomonas cells responded to a broad range of TRIA concentrations that were at least one order of magnitude above the optimum concentration established for higher plants. The necessity for larger concentrations of TRIA may be due to destabilizing effects of Ca²⁺ and K⁺ present in the Chlamydomonas growth medium. These ions caused flocculation of the colloidally dispersed TRIA in apparent competition with binding of [¹⁴C]TRIA to Chlamydomonas cells. Octacosanol inhibited the effect of TRIA on photosynthetic CO₂ assimilation. TRIA treatment did not alter the distribution of ¹⁴C-label among photosynthetic products. The effect of TRIA on photosynthetic CO₂ assimilation increased with time after treatment up to 3 days. Chlamydomonas cells that had been grown at low-CO₂ (air) did not respond to TRIA, and transfer of high-CO₂ (5%) grown cells that had responded to TRIA to a low-CO₂ atmosphere resulted in a loss of the effect of TRIA. The effect of pH on photosynthetic CO₂ assimilation indicated that CO₂ is probably the species of inorganic carbon utilized by control and TRIA-treated Chlamydomonas cells.     

Effect of Bursaphelenchus xylophilus on the Assimilation and Translocation of 14 C in Pinus sylvestris

The effect of wound, wound + water, wound + Bursaphelenchus xylophilus culture filtrate, or wound + lethal B. xylophilus doses on the assimilation and translocation of ¹⁴C by 8-month-old Pinus sylvestris seedlings was tested. In two separate experiments, pine seedlings were exposed to 28.35 μCi of ¹⁴CO₂ for 20 minutes below or above (to the pine shoot leader) the point of nematode inoculation. After 2 and 4 hours of dark adaptation, 80% ethanol soluble ¹⁴C tissue extracts were determined by liquid scintillation counting. Nematode infection significantly (P = 0.05) decreased ¹⁴C assimilation. Treatments translocated less than 6% of the total amount of the fixed ¹⁴C and translocation generally decreased with increasing size of nematode inoculum. However, infected pines translocated a greater proportion of the amount of ¹⁴C fixed per gram of exposed nematode-plant tissue than did the control pines. The lower levels of photoassimilate entering the plant system probably resulted in a reduced metabolic capacity in B. xylophilus-infected pine seedlings. The effect on photosynthesis could be one of the key factors leading to death of pines through starvation, and it is possible that it was preceded by an effect on related physiological processes such as water uptake.     

CO(2) Assimilation by Etiolated Hordeum vulgare Seedlings during the Onset of Photosynthesis

The assimilation of CO₂ by etiolated Hordeum vulgare seedlings during an illumination period indicates a conversion of the organisms to autotrophy.

After 1 hour illumination, increases in the photo-assimilation of CO₂ are observed and the distribution of C¹⁴ in the soluble fraction of the plants is predominantly in intermediates of the Calvin cycle.