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Thus far all attempts to isolate CO2 fixing chloroplasts from pine have failed. In this paper it is proposed that resin acids present in pine needles partition into membranes during chloroplast isolation and interfere with specific reactions of the Calvin cycle. CO2 fixation by isolated spinach chloroplasts was strongly inhibited by the introduction of a suspension of chloroplasts isolated from Pinus sylvestris L. A partially purified organic extract obtained from chloroplasts of this pine species also strongly inhibited CO2 fixation by the spinach chloroplasts. The major inhibitory compounds from the organic extract were identified as a mixture of resin acids by gas-liquid chromatography and mass spectrometry. Two resin acids, abietic acid and dehydroabietic acid, were tested for inhibitory activity. Both resin acids were potent inhibitors of photosynthetic CO2 fixation, with dehydroabietic acid being about three times more potent than abietic acid. [ABSTRACT FROM AUTHOR]

The after-effect of wind on photosynthesis and transpiration of Festuca arundinacea Schreb., was determined. Following a period of exposure in a controlled environment wind tunnel the wind-treated plants showed reduced rates of photo-synthesis when compared with the controls under standard conditions. Evaporation from paper model tillers was measured and the boundary layer resistance was shown to be low in all but very low wind speeds. Analysis of CO2 and H2O diffusion pathways indicated that mesophyll resistance in wind-treated plants was higher whilst leaf surface resistance was lower than in the controls. The high mesophyll resistance in the wind-treated plants was attributed to reduced water content. [ABSTRACT FROM AUTHOR]

Rice (Oryza sativa L.) callus cultures modified the atmosphere of the headspace of the vessel used for culture maintenance by producing carbon dioxide, ethanol and ethylene, while utilizing oxygen. Small quantities of acetaldehyde and ethane were also measured in one cultivar. Under these conditions of culture maintenance, callus from some cultivars were much more difficult to keep alive than callus from others. The largest proportion of necrotic callus was produced from cultures growing under conditions of high ethylene production and low oxygen utilization. When callus was exposed to a controlled flowing gas mixture similar to that accumulated above necrotic callus, growth of 2 necrosis-susceptible cultivars was more strongly inhibited than growth of 2 necrosis-tolerant cultivars. The poor callus growth was associated with higher ethylene production and a lower rate of oxygen utilization. [ABSTRACT FROM AUTHOR]

Current-year shoots of Sitka spruce (Picea Sitchensis (Bong.) Carr.) were removed from the forest canopy. After steady-state rates of net photosynthesis were obtained in a leaf chamber, the shoots were excised in air and removed at different times to establish a relationship between net photosynthesis and xylem water potential, The experiment was repeated at five ambient carbon dioxide concentrations. Net photosynthesis remained constant over a wide range of xylem water potential and increased linearly with ambient carbon dioxide concentration between 20 and 300 cm3 m-3. At low water potential net photosynthesis declined at each ambient carbon dioxide concentration and there was little difference in the potential (± 0.05 MPa) at which zero photosynthesis was observed. There was a small increase in the CO2 compensation concentration at low xylem water potential, but calculated mesophyll conductance still declined at low water potential after correction for this change in compensation concentration. Mesophyll conductance reached zero within the same range of water potential as net photosynthesis. The results suggested that the non-stomatal contribution to the decline of photosynthesis was approximately 30% until almost complete stomatal closure occurred. [ABSTRACT FROM AUTHOR]

The extent and manner of ethylene involvement in germination of lettuce (Lactuca sativa L. cv. Mesa 659) seed at a moderate temperature (20°C) were investigated. Inhibition of germination at low pressure of 150 mmHg in an oxygen flow-through system was alleviated to a marked extent by ethylene. Carbon dioxide was ineffective by itself but caused further alleviation of inhibition in presence of ethylene and oxygen. Other seed treatments which partially alleviated the inhibition caused by low pressure included soaking in 10μM of fusicoccin and a prior treatment with acetone. Of the two ethylene adsorbents used, Purafil was more effective in inhibiting germination in a closed container. Although the ethylene biosynthesis inhibitor, 8-hydroxyquinoline (1.0 mM), showed no effect on ethylene production, it markedly inhibited germination and the effect was partially reversed by ethylene and GA3. An ethoxy analog of rhizobitoxine, on the other hand, had little or no effect on germination but strongly inhibited the ethylene production. Although no causal relation of ethylene to germination was established, the evidence presented here implicates ethylene, together with other gases, in the regulation of germination. [ABSTRACT FROM AUTHOR]

The role of malate decarboxylation as a source of CO2 and NADPH for the evolution of photosynthesis of isolated maize bundle-sheath strands has been investigated. The bundle-sheath cells were supplied with malate plus NADP, in the presence of intermediates of the Calvin cycle to increase the rate of CO2 fixation. The effects of malate addition on the rate of 3 phosphogly- cerate synthesis, with non-saturating concentrations of bicarbonate., can be explained by an increase of the cellular pool of CO2 in the cells due to malate decarboxylation. The CO2 reacting with RuDP to give phosphoglycerate corresponds effectively to carbon atom 4 of malate. Malate addition produces an enhancement of the rate of CO2 incorporation which is much more important when the reducing power is the limiting process for the evolution of the Calvin cycle (with phosphoglycerate as added substrate and/or in the presence of DCMU). These results demonstrate the utilization of NADPH produced by malate decarboxylation for the regeneration of RuDP. NADPH can also reverse the reaction of malate decarboxylation and gives rise to a synthesis of malate by carboxylation of pyruvate. In contrast, the pattern of 14C distribution among compounds is not strongly modified by malate addition. This result suggests that PGA reduction in the whole. leaf must occur also in mesophyll cells to allow correctregeneration of the reduced compounds of the photosynthetic cycle. [ABSTRACT FROM AUTHOR]

Isolated bundle-sheath (ES) strands from leaves of mature maize plants show enhanced rates of CO2 fixation in the presence of reduced intermediates of the photosynthetic cycle (R5P, DHAP, FruDP …). 3PGA is the major labelled product of 14CO2 fixation whatever the substrate added. CO2 fixation is much lower with PGA than with reduced intermediates, suggesting a limited capacity of the cells to regenerate RuDP (the CO2-acceptor) from PGA. These two experimental facts, which are characteristic features of bundle-sheath photosynthesis for maize (a species with agranal bundle-sheath chloroplasts) indicate that photosystem II activity is a limiting factor for the evolution of the bundle-sheath photosynthetic process. Nevertheless, a reducing capacity arises as proved by sensitivity of CO2 fixation to DCMU, particularly when PGA is added to the bundle-sheath. PGA synthesis occurs, in the presence of non-limiting amounts of CO2, according to the equation: RuDP + CO2→2 PGA; the oxygen effect on 14CO2 fixation, at lower CO2 concentration, is interpreted as a dilution effect of the internal pool of 14CO2 by unlabelled CO2 generated by photorespiration. [ABSTRACT FROM AUTHOR]

Cucumber (Cucumis sativus L. cv. Poinsett 76) seeds were chilled at 2.5°C in a study of the chilling sensitivity and recovery of radicle tissue. The effect of chilling on radicle growth and the production of carbon dioxide and ethylene was measured. Chilling sensitivity of radicles increased as they grew from 1 to 7 mm in length. The length not the age of the radicles, determined the level of chilling sensitivity. Apical tissue was most sensitivity to chilling and slowest to recover from chilling, followed by subapical and basal tissue. Our data demonstrate that the chilling sensitivity of young seedling radicles differs along their length and that the rapid chilling-induced inhibition of elongation is probably due to an inability of meristematic cells to remain viable and active when chilled. [ABSTRACT FROM AUTHOR]

The labeling of intermediate compounds and photosynthetic cofactors during photosynthesis and periods of darkness by Chlorella pyrenoidosa in the presence of 32P-labeled phosphate and 14CO2 have been investigated. Algae adapted to photo- synthesis in air were used, and the level of carbon dioxide was maintained at approximately 0.04% and at constant specific radioactivity during the course of the experiments. The transient changes which occur in the levels of labeled fructose-1,6-diphosphate and in sedoheptulose-1,7-diphosphate, and in the corresponding monophosphates when the light is turned off suggest a light activation of the diphosphatase enzymes which decays after about 2 minutes of darkness. It is suggested that a light-dark switch in enzymic activities permits photosynthesis and glycotysis to occur in light and dark respectively with the same enzymic apparatus. The greatly diminished rate of disappearance ot the carboxylation substrate, ribulose-1,5-diphosphate, after about 2 minutes suggests that there is also a light activation of the carboxylation reaction in vivo. Large transient changes in the level of pyrophosphate between light and dark indicate that there may be an unstable co-factor which decomposes to give pyrophosphate during or after killing of the algal cells. The possibility that this cofactor is involved in an activation of carbon dioxide for the carboxylation reaction in vivo is suggested. Light-dark transient changes in labeling of other compounds of the photosynthetic carbon reduction cycle and related compounds were determined, and possible significance of these changes is discussed. [ABSTRACT FROM AUTHOR]

Cellular constituents(chloroplasts,sap and mitochondrial), separated from spinach leaves, were allowed to photosynthesize in the presence of radio active bicarbonate. The radiocarbon fixed by the chloroplasts was distributed mainly in the phosphate ester while the radiocarbon fixed by the sap was located mostly in the amino acids. the mitochondrial fraction fixed very little radioactive carbon dioxide. the rate of carbon dioxide fixation by the recombined mixture of sap and chloroplasts was greater than the sum of the separate components. the distribution pattern of the fixed radiocarbon of the recombined mixture, however, was qualitatively similar to a combination of the radiocarbon distribution of the separated chloroplasts and sap. The results of experiments carried out with these cellular constituents in the dark and in the presence of other substrates, labelled and unlabelled, are discussed. [ABSTRACT FROM AUTHOR]

1. The impression is conveyed through the literature that studies of the root respiration of intact plants usually constitute a minor and necessary part of more comprehensive works. This fact naturally influences the methods used, and it must be stated that these do not fulfil satisfactorily the conditions that can be reasonably expected for methods intended to elucidate the problem of the course of respiration in intact plants. 2. The method described in this paper (The Tonometer Method) allows frequent and simultaneous determinations of oxygen and carbon dioxide during measurements of root respiration in plants which have their roots in a closed system surrounded by circulating nutrient solution. 3. The tonometer method provides wide possibilities for carrying out arbitrary and rapid changes of the environmental factors of the roots as well as those of other parts of the plant, and for studying the influence of such changes on root respiration. 4. Carbon dioxide and oxygen determinations may be carried out with mean errors of 3.5 and 1.9 per cent, respectively. [ABSTRACT FROM AUTHOR]

The rapid assimilation of small quantities of ammonium, nitrite and nitrate-N by nitrogen-starved cells of Chlorella vulgaris is accompanied by high rates of gas exchange. When all the added nitrogen has been assimilated the rates of gas exchange return to the control values. The total volume of oxygen taken up during the period of nitrogen assimilation is about the same whichever nitrogen source is added but the rate is highest with ammonium-N and lowest with nitrate-N. On the other hand, the rate of carbon dioxide production is much the same whichever salt is added but the total volume of carbon dioxide produced is greatest when nitrate-N is added and least with ammonium-N. The quantities of oxygen absorbed and carbon dioxide produced agree with those expected if ammonium, nitrite and nitrate-N are all assimilated to the same final products and if carbohydrate is the carbon source in the cells. A high respiration rate also follows the addition of hydroxylamine but the gas exchange differs markedly from that expected if hydroxylamine were assimilated to the same products as the other nitrogen sources. [ABSTRACT FROM AUTHOR]

This article studies the evidence for the participation of cytochrome oxidase in photosynthetic fixation of carbon dioxide. A researcher measured the utilization of carbon dioxide by cut leaves with a continous recording method, and found that if leaves were exposed to carbon dioxide mixed with pure nitrogen, the rate of photosytithetic assimilation of carbon dioxide was slowed down after short pt-riods of darkness under these anaerobic conditions. The inhibition was not reversed by exposure to light in the carbon dioxide-nitrogen mixture, but it was reversed by a short exposure to air in darkness.

1. The oxygen uptake and carbon dioxide production of intact and dissected buds has been measured, and the effect of oxygen percentage and seasonal changes on these determined. 2. Oxygen partial pressure curves show the oxygen uptake of intact buds to be normally limited by the rate of oxygen diffusion to the respiring cells. 3. The oxygen uptake of dissected bud parts has been found to be limited at much lower oxygen percentages than in the case of intact buds. 4. Although lowering the temperature lowers the rate of oxygen uptake at any given oxygen percentage, it does not greatly change the overall shape of the oxygen partial pressure curve. 5. Observations on seasonal changes in the respiratory behavior of intact buds show that the oxygen limitation is most severe during late summer, is lessened during the autumn when the respiratory capacity of the buds is depressed, and then is largely removed in late winter and early spring as the respiratory capacity of the buds increases.. (6). Dissected bud parts show a strong »Pasteur» effect; theN2>Qco2/Qo2 air ratio for the bud scales is near 1.0, and for the growing region near 1.4. 7. The limitation of oxygen uptake is reflected by a high aerobic carbon dioxide production resulting in a respiratory quotient greater than unity. 8. The high respiratory quotients have been observed during the months of August and September when the limitation of oxygen uptake is most severe; the H.Q. differs very little from unity when the limitation is not so severe. 9. Lowering the temperature lowers aerobic carbon dioxide production more rapidly than oxygen uptake. 10. These observations are discussed with reference to a growth inhibitor in buds, and a working hypothesis of the nature of rest in these structures is presented. [ABSTRACT FROM AUTHOR]

Predicted increases in atmospheric concentration of carbon dioxide (CO2) coupled with increased temperatures and drought are expected to strongly influence the development of most of the plant species in the world, especially in areas with high risk of desertification like the Mediterranean basin. Helianthemum almeriense is an ecologically important Mediterranean shrub with an added interest because it serves as the host for the Terfezia claveryi mycorrhizal fungus, which is a desert truffle with increasingly commercial interest. Although both plant and fungi are known to be well adapted to dry conditions, it is still uncertain how the increase in atmospheric CO2 will influence them. In this article we have addressed the physiological responses of H. almeriense × T. claveryi mycorrhizal plants to increases in atmospheric CO2 coupled with drought and high vapor pressure deficit. This work reports one of the few estimations of mesophyll conductance in a drought deciduous Mediterranean shrub and evaluates its role in photosynthesis limitation. High atmospheric CO2 concentrations help desert truffle mycorrhizal plants to cope with the adverse effects of progressive drought during Mediterranean springs by improving carbon net assimilation, intrinsic water use efficiency and dispersal of the species through increased flowering events. [ABSTRACT FROM AUTHOR]

Global warming and the consequent climate change is one of the major environmental challenges we are facing today. The driving force behind the rise in temperature is our fossil‐based economy, which releases massive amounts of the greenhouse gas carbon dioxide into the atmosphere. In order to reduce greenhouse gas emission, we need to scale down our dependency on fossil resources, implying that we need other sources for energy and chemicals to feed our economy. Here, plants have an important role to play; by means of photosynthesis, plants capture solar energy to split water and fix carbon derived from atmospheric carbon dioxide. A significant fraction of the fixed carbon ends up as polysaccharides in the plant cell wall. Fermentable sugars derived from cell wall polysaccharides form an ideal carbon source for the production of bio‐platform molecules. However, a major limiting factor in the use of plant biomass as feedstock for the bio‐based economy is the complexity of the plant cell wall and its recalcitrance towards deconstruction. To facilitate the release of fermentable sugars during downstream biomass processing, the composition and structure of the cell wall can be engineered. Different strategies to reduce cell wall recalcitrance will be described in this review. The ultimate goal is to obtain a tailor‐made biomass, derived from plants with a cell wall optimized for particular industrial or agricultural applications, without affecting plant growth and development. [ABSTRACT FROM AUTHOR]

Three different species of Brassica, with differential salt sensitivity were used to understand physiological mechanisms of salt tolerance operating in these species and to evaluate the relative contribution of different strategies to cope with salt load. Brassica napus was the most tolerant species in terms of the overall performance, with Brassica juncea and Brassica oleracea being much more sensitive to salt stress with no obvious difference between them. While prominent reduction in net CO2 assimilation was observed in both sensitive species, physiological mechanisms beyond this reduction differed strongly. Brassica juncea plants possessed high osmotolerance and were able to maintain high transpiration rate but showed a significant reduction in leaf chlorophyll content and efficiency of leaf photochemistry. On the contrary, B. oleracea plants possessed the highest (among the three species) tissue tolerance but showed a very significant stomatal limitation of photosynthesis. Electrophysiological experiments revealed that the high tissue tolerance in B. oleracea was related to the ability of leaf mesophyll cells to maintain highly negative membrane potential in the presence of high apoplastic Na+. In addition to high osmotolerance, the most tolerant B. napus showed also lesser accumulation of toxic Na+ and Cl− in the leaf, possessed moderate tissue tolerance and had a superior K+ retention ability. Taken together, the results from this study indicate that the three Brassica species employ very different mechanisms to cope with salinity and, despite its overall sensitivity to salinity, B. oleracea could be recommended as a valuable 'donor' of tissue tolerance genes to confer this trait for marker-assisted breeding programs. [ABSTRACT FROM AUTHOR]

Jatropha (Jatropha curcas) is a non-edible oil producing plant which is being advocated as an alternative biofuel energy resource. Its ability to grow in diverse soil conditions and minimal requirements of essential agronomical inputs compared with other oilseed crops makes it viable for cost-effective advanced biofuel production. We designed a study to investigate the effects of elevated carbon dioxide concentration ([CO2]) (550 ppm) on the growth, reproductive development, source-sink relationships, fruit and seed yield of J. curcas. We report, for the first time that elevated CO2 significantly influences reproductive characteristics of Jatropha and improve its fruit and seed yields. Net photosynthetic rate of Jatropha was 50% higher in plants grown in elevated CO2 compared with field and ambient CO2-grown plants. The study also revealed that elevated CO2 atmosphere significantly increased female to male flower ratio, above ground biomass and carbon sequestration potential in Jatropha (24 kg carbon per tree) after 1 year. Our data demonstrate that J. curcas was able to sustain enhanced rate of photosynthesis in elevated CO2 conditions as it had sufficient sink strength to balance the increased biomass yields. Our study also elucidates that the economically important traits including fruit and seed yield in elevated CO2 conditions were significantly high in J. curcas that holds great promise as a potential biofuel tree species for the future high CO2 world. [ABSTRACT FROM AUTHOR]

Systems for exposing plants to elevated concentrations of CO2 may expose plants to pulses of CO2 concentrations considerably above the control set point. The importance of such pulses to plant function is unknown. Single leaves of wheat (Triticum aestivum cv Choptank) and rice (Oryza sativa cv Akitakomachi) were exposed for 30 minutes to pulses of elevated CO2 similar to the frequency, duration and magnitude of pulses observed in free‐air CO2 enrichment systems. Stomatal conductance decreased within a few minutes of exposure to once per minute pulses of high CO2 of all the durations tested, in both species. Both species had 20–35% lower stomatal conductance for at least 30 min after the termination of the pulses. After the pulses had stopped, in all cases photosynthesis was below the values expected for the observed substomatal CO2 concentration, which suggests that either patchy stomatal closure occurred or that photosynthesis was directly inhibited. It was also found that a single, 2 s pulse of elevated CO2 concentration reaching a maximum of 1000 µmol mol−1 decreased stomatal conductance in both species. On the basis of these results, it is probable that plants in many CO2 enrichment systems have lower photosynthesis and stomatal conductance than would plants exposed to the same mean CO2 concentration but without pulses of higher concentration. [ABSTRACT FROM AUTHOR]

CO2 fixation in mosses saturates at moderate irradiances. Relative electron transport rate (RETR) inferred from chlorophyll fluorescence saturates at similar irradiance in shade species (e.g. Plagiomnium undulatum, Trichocolea tomentella), but many species of unshaded habitats (e.g. Andreaea rothii, Schistidium apocarpum, Sphagnum spp. and Frullania dilatata) show non-saturating RETR at high irradiance, with high non-photochemical quenching (NPQ). In P. undulatum and S. apocarpum, experiments in different gas mixtures showed O2 and CO2 as interchangeable electron sinks. Nitrogen + saturating CO2 gave high RETR and depressed NPQ. In S. apocarpum, glycolaldehyde (inhibiting photosynthesis and photorespiration) depressed RETR in air more at low than at high irradiance; in CO2-free air RETR was maintained at all irradiances. Non-saturating electron flow was not suppressed in ambient CO2 with 1% O2. The results indicate high capacity for oxygen photoreduction when CO2 assimilation is limited. Non-saturating light-dependent H2O2 production, insensitive to glycolaldehyde, suggests that electron transport is supported by oxygen photoreduction, perhaps via the Mehler-peroxidase reaction. Consistent with this, mosses were highly tolerant to paraquat, which generates superoxide at photosystem I (PSI). Protection against excess excitation energy in mosses involves high capacity for photosynthetic electron transport to oxygen and high NPQ, activated at high irradiance, alongside high reactive oxygen species (ROS) tolerance. [ABSTRACT FROM AUTHOR]

Chlamydomonas acidophila Negoro is a green algal species abundant in acidic waters (pH 2–3.5), in which inorganic carbon is present only as CO2. Previous studies have shown that aeration with CO2 increased its maximum growth rate, suggesting CO2 limitation under natural conditions. To unravel the underlying physiological mechanisms at high CO2 conditions that enables increased growth, several physiological characteristics from high- and low-CO2-acclimated cells were studied: maximum quantum yield, photosynthetic O2 evolution (Pmax), affinity constant for CO2 by photosynthesis (K0.5,p), a CO2-concentrating mechanism (CCM), cellular Rubisco content and the affinity constant of Rubisco for CO2 (K0.5,r). The results show that at high CO2 concentrations, C. acidophila had a higher K0.5,p, Pmax, maximum quantum yield, switched off its CCM and had a lower Rubisco content than at low CO2 conditions. In contrast, the K0.5,r was comparable under high and low CO2 conditions. It is calculated that the higher Pmax can already explain the increased growth rate in a high CO2 environment. From an ecophysiological point of view, the increased maximum growth rate at high CO2 will likely not be realised in the field because of other population regulating factors and should be seen as an acclimation to CO2 and not as proof for a CO2 limitation. [ABSTRACT FROM AUTHOR]

Unicellular green alga Chlorella minutissima, grown under extreme carbon dioxide concentrations (0.036–100%), natural temperature and light intensities (Mediterranean conditions), strongly increase the microalgal biomass through photochemical and non-photochemical changes in the photosynthetic apparatus. Especially, CO2 concentrations up to 10% enhance the density of active reaction centers (RC/CSo), decrease the antenna size per active reaction center (ABS/RC), decrease the dissipation energy (DIo/RC) and enhance the quantum yield of primary photochemistry (Fv/Fm). Higher CO2 concentrations (20–25%) combine the above-mentioned photochemical changes with enhanced non-photochemical quenching of surplus energy, which leads to an enhanced steady-state fraction of ‘open’ (oxidized) PSII reaction centers (qp), and minimize the excitation pressure of PSII (1 − qp) under very high light intensities (approximately 1700 μmol m−2 s−1 maximal value), avoiding the photoinhibition and leading to an enormous biomass production (approximately 2500%). In conclusion, these extreme CO2 concentrations – about 1000 times higher than the ambient one – can be easily metabolized from the unicellular green alga to biomass and can be used, on a local scale at least, for the future development of microalgal photobioreactors for the mitigation of the factory-produced carbon dioxide. [ABSTRACT FROM AUTHOR]

The objectives of this research were to determine the influence of hypobaria (reduced atmospheric pressure) and reduced partial pressure of oxygen (pO2) [hypoxia] on carbon dioxide (CO2) assimilation (CA), dark-period respiration (DPR) and growth of lettuce ( Lactuca sativa L. cv. Buttercrunch). Lettuce plants were grown under variable total gas pressures [25 and 101 kPa (ambient)] at 6, 12 or 21 kPa pO2 (approximately the partial pressure in air at normal pressure). Growth of lettuce was comparable between ambient and low total pressure but lower at 6 kPa pO2 (hypoxic) than at 12 or 21 kPa pO2. The specific leaf area of 6 kPa pO2 plants was lower, indicating thicker leaves associated with hypoxia. Roots were most sensitive to hypoxia, with a 50–70% growth reduction. Leaf chlorophyll levels were greater at low than at ambient pressure. Hypobaria and hypoxia did not affect plant water relations. While hypobaria did not adversely affect plant growth or CA, hypoxia did. There was comparable CA and a lower DPR in low than in ambient total pressure plants under non-limiting CO2 levels (100 Pa pCO2, nearly three-fold that in normal air). The CA/DPR ratio was higher at low than at ambient total pressure, particularly at 6 kPa pO2– indicating a greater efficiency of CA/DPR in low-pressure plants. There was generally no significant interaction between hypoxia and hypobaria. We conclude that lettuce can be grown under subambient pressure (≅25% of normal earth ambient total pressure) without adverse effects on plant growth or gas exchange. Furthermore, hypobaric plants were more resistant to hypoxic conditions that reduced gas exchange and plant growth. [ABSTRACT FROM AUTHOR]

Leaf water potentials below threshold values result in reduced stomatal conductance (gs). Stomatal closure at low leaf water potentials may serve to protect against cavitation of xylem. Possible control of gs by leaf water potential or hydraulic conductance was tested by drying the rooting medium in four herbaceous annual species until gs was reduced and then lowering the [CO2] to determine whether gs and transpiration rate could be increased and leaf water potential decreased and whether hydraulic conductance was reduced at the resulting lower leaf water potential. In all species, low [CO2] could reverse the stomatal closure because of drying despite further reductions in leaf water potential, and the resulting lower leaf water potentials did not result in reductions in hydraulic conductance. The relative sensitivity of gs to internal [CO2] in the leaves of dry plants of each species averaged three to four times higher than in leaves of wet plants. Two species in which gs was reputed to be insensitive to [CO2] were examined to determine whether high leaf to air water vapor pressure differences (D) resulted in increased stomatal sensitivity to [CO2]. In both species, stomatal sensitivity to [CO2] was indeed negligible at low D, but increased with D, and low [CO2] partly or fully reversed closure caused by high D. In no case did low leaf water potential or low hydraulic conductance during drying of the air or the rooting medium prevent low [CO2] from increasing gs and transpiration rate. [ABSTRACT FROM AUTHOR]

Laser photoacoustic spectroscopy continuously quantified the ethylene (C2H4) produced by strawberry flowers and fruits developing in planta. C2H4 was first detected as flower buds opened and exhibited diurnal oscillations (to approximately 200 pl flower−1 h−1) before petal abscission. Exogenous application of silver thiosulphate (STS) to detached flowers inhibited petal abscission and flower senescence. In fruit, C2H4 production was maintained at a ‘low level’ (10–60 pl fruit−1 h−1) until fruit expanded when levels increased in a diurnal pattern (to 200 pl fruit−1 h−1). After expansion, C2H4 production declined to a low level until fruit attained the red-ripe stage for at least 24 h. After this time, C2H4 levels increased linearly (no diurnal fluctuation) to approximately 1 nL fruit−1 h−1. Twenty-four hours after the re-initiation of C2H4 production by red fruit, CO2 levels increased approximately three-fold, indicative of a respiratory climacteric. STS applied to fruits developing in planta and dissected fruit parts ex situ established that C2H4 production is regulated by negative feedback until fruits had expanded. The C2H4 produced by red-ripe fruit was regulated by positive feedback. Anti-1-amino-cyclopropane-1-carboxylic acid oxidase IgG localization identified immunoreactive antigens of 40 and 30 kDa (Mr) within the fruit achenes of expanding and red-ripe fruit. Analysis of dissected fruit showed that seed C2H4 accounts for 50% the C2H4 that is detectable from ripe fruit. [ABSTRACT FROM AUTHOR]

Twigs of many woody plants possess chlorenchyma under a well-developed periderm which lacks stomata and impedes both gas diffusion and light penetration. The so-called corticular photosynthesis, occurring in the shade and under extremely high CO2 concentrations, was probed in this study through in vivo chlorophyll fluorescence measurements. Field comparisons between twigs and corresponding leaves in five species indicated that both the dark- and light-adapted PSII photochemical efficiencies are considerably lower in twigs at all incident photon fluence rates, in spite of the significant attenuation of solar radiation by the periderm. Light saturation curves for linear electron transport rates (corrected according to the actual light intensities reaching twig chlorenchyma) were compatible with a shade-acclimated photosynthetic machinery, showing very low maximum electron transport rates (at approximately 5% of the corresponding leaf values) and threshold irradiances for light saturation. However, removing periderms from twig segments (i.e. relieving the twig interior form the high CO2 partial pressures) considerably improved the light-adapted (but not the dark-adapted) PSII photochemical efficiency, allowing the assumption that the high internal CO2 levels may interfere with the smooth functioning of photosynthesis. Indeed, laboratory experiments with twig segments equilibrated under various CO2 levels (0.036–20%), resulted in a progressive decrease of light-adapted PSII photochemical yield, with the values obtained at 20% CO2 being similar to those obtained with intact twigs in the field. Further experiments indicated that high CO2 combined with high light suppressed the development of a photoprotective non-photochemical quenching through a reduction of its fast relaxing component, accompanied by a higher risk of photoinhibition. It is suggested that high internal CO2 concentrations in twigs impede photosynthesis possibly through acidification of protoplasm and impairment of the pH-dependent high energy state quenching followed by reduction in the efficiency of heat dissipation. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the direct effect of elevated atmospheric CO2 concentrations on leaf respiration in darkness (R) over a broad range of measurement temperatures. Our aim was to further elucidate the underlying mechanism(s) of the often‐reported inhibition of leaf R by a doubling of the atmospheric CO2 concentration. Experiments were conducted using two species of Plantago that differed in maximum relative growth rate (fast‐growing Plantago lanceolata L. and the slow‐growing P. euryphylla Briggs, Carolin & Pulley). Rates of leaf respiration (R) were measured at atmospheric CO2 concentrations ranging from 75 to 2000 µmol mol−1 at temperatures from 12 to 42°C. R was measured as CO2 release with a portable gas exchange system with infrared gas analysers. Our hypothesis was that the changes in temperature alter the flux coefficient (i.e. the extent to which changes in potential enzyme activity has an effect on the rate of a reaction) of enzymes potentially affected by CO2. Initial analysis of our results suggested that R was inhibited by elevated CO2 in both species, with the apparent degree of inhibition being greatest at low temperature. Moreover, the apparent degree of inhibition following a doubling of atmospheric CO2 concentration from 350 to 700 µmol mol−1 was similar to that reported by several previous studies (approximately 14% and 26% for P. lanceolata and P. euryphylla, respectively) at a temperature equal to the mean of the previous studies. However, subsequent correction for diffusion leaks of CO2 across the gas exchange's cuvette gaskets revealed that no significant inhibition had occurred in either species, at any temperature. The inhibitory effect of elevated CO2 on leaf respiratory CO2 release reported by previous studies may therefore have been overestimated. [ABSTRACT FROM AUTHOR]

Recent research has shown that nodule nitrogen fixation is limited under a wide range of environmental constraints by lowered carbon flux within the nodule due to down-regulation of sucrose synthase activity. The aim of this work was to elucidate whether an increase in both carbon flux and activity of enzymes of carbon metabolism in nodules may lead to an increased nitrogen fixation. We report the effects caused by a continuous exposure to atmospheric CO2 enrichment in nodulated pea plants. CO2 enrichment led to an enhanced whole-plant growth and increased nodule biomass. Moreover, nodules of plants grown at increased CO2 showed a higher sugar content as well as enhancement of some activities related to nodule carbon metabolism, such as sucrose synthase, UDP glucose pyrophosphorylase and phosphoenolpyruvate carboxylase. Indeed, acetylene reduction activity, measured by the classical technique, was increased more than four times. However, when specific nitrogen fixation was determined as hydrogen evolution, no significant differences were detected, consistent with the lack of changes of enzymes involved in nitrogen metabolism such as glutamate synthase and aspartate aminotransferase. These results are discussed in the context of the regulation of nitrogen fixation and nodule metabolism. [ABSTRACT FROM AUTHOR]

Dactylis glomerata was grown hydroponically in a controlled environment at ambient (360 μl l-1) or elevated (680 μl l-1) CO2 and four concentrations of nitrogen (0.15, 0.6, 1.5 and 6.0 mM NO3 -), to test the hypothesis that reduction of photosynthetic capacity at elevated [CO2] is dependent on N availability and mediated by a build-up of non-structural carbohydrates. Photosynthetic capacity of the youngest fully expanded leaf (leaf 5, 2 days after full expansion) was reduced in CO2-enriched plants at low, but not high N supply and so the stimulation of net photosynthesis by CO2 enhancement was less at low than at high N supply. CO2 enrichment resulted in a decrease in ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) content on a leaf area basis at 0.6 and 1.5 mM NO3 -, but not at 0.15 and 6.0 mM NO3 -, and had no effect on the total N content of the leaf on an area basis. However, decreases in Rubisco content could be primarily accounted for by a decrease in total N content of leaves, independent of [CO2]. A doubling of the Rubisco content by increasing the N supply beyond 0.6 mM had only a marginal effect on the maximum carboxylation velocity in vivo, suggesting that the fraction of inactive Rubisco increased with increasing N supply. Although CO2-enriched plants accumulated more non-structural carbohydrates in the leaf, the reduction of photosynthetic capacity at low N supply was not mediated simply by a build-up of carbohydrates. In D. glomerata, the photosynthetic capacity was mainly determined by the total N content of the leaf. [ABSTRACT FROM AUTHOR]

Spring wheat (Triticum aestivum L. cv. Dragon) was exposed to elevated carbon dioxide (CO2), alone (1995) or in combination with two levels of increased ozone (O3) (1994) or increased irrigation (1996) during three successive growing seasons as part of the EU ESPACE-wheat programme and conducted in open-top chambers (OTCs) and ambient air (AA) plots at Östad, 50 km north-east of Göteborg, Sweden. Doubling the CO2 concentration had a positive effect on grain yield in all 3 years (+21, +7 and +11%, respectively), although only statistically significant in 1994. That year was characterised by a warm and dry summer in comparison with 1995 and 1996, in which the summers were more humid and typical for south-west Sweden. In 1994, the CO2-induced increase in grain yield was associated with an increase in the duration of the green leaf area, a positive effect on straw yield and on the number of ears per square metre and a negative effect (-13%) on grain protein concentration. Harvest index was unaffected by the elevated CO2 concentration. The only statistically significant effect of elevated CO2 in 1995 was a decrease in the grain protein concentration (-11% in both CO2 concentrations), and in 1996 an increase (+21%) in the straw yield. In 1996 the soil water potential was less negative in elevated CO2, which is likely to reflect a lower water consumption of these plants. Addition of extra O3 significantly affected the grain yield (-6 and -10%, respectively) and the 1000-grain weight negatively (-3 and -6%). Statistically significant interactions between CO2 and O3 were obtained for the number of ears per unit area and for the 1000-grain weight. The 1000-grain weight was negatively affected by O3 in low CO2, but remained unaffected in the high CO2 treatment. There was a significant decrease (-6%) in the grain protein concentration induced by elevated irrigation. The chambers, compared with AA plots, had a positive effect on plant development and on grain yield in all 3 years. [ABSTRACT FROM AUTHOR]

The effect of 700 μmol CO2 mol-1, 200 nmol ozone mol-1 and a combination of the two on carbon allocation was examined in Pinus halepensis co-cultured with Betula pendula in symbiosis with the ectomycorrhizal fungus Paxillus involutus. The results show that under low nutrient and ozone levels, elevated CO2 has no effect on the growth of B. pendula or P. halepensis seedlings nor on net carbon partitioning between plant parts. Elevated CO2 did not enhance the growth of the fungus in symbiosis with the birch. On the other hand, ozone had a strong negative effect on the growth of the birch, which corresponded with the significantly reduced growth rates of the fungus. Exposure to elevated CO2 did not ameliorate the negative effects of ozone on birch; in contrast, it acted as an additional stress factor. Neither ozone nor CO2 had significant effects on biomass accumulation in the pine seedlings. Ozone stimulated the spread of mycorrhizal infection from the birch seedlings to neighbouring pines and had no statistically significant effects on phosphoenolpyruvate carboxylase (PEPC) or ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity in the pine needles or on PEPC activity in pine roots. [ABSTRACT FROM AUTHOR]

Different isoenzymes of carbonic anhydrase (CA; EC 4.2.1.1) have been separated using thalli of the red macroalga Porphyra leucosticta Thuret in Le Jolis. Homogenates of the thallus were centrifuged in order to separate soluble and membrane proteins. The fraction containing membrane proteins was subdivided by centrifuging into two fractions: green and nongreen membrane proteins. CA activity was detected in all the fractions. Because external CA (measured on intact thallus) represented 15% of total activity, it was concluded that most of the CA (ca. 80%) was soluble and internal. Direct evidence regarding the different function of external and internal CA was obtained by determining the effects on photosynthesis of two specific CA inhibitors with different capacity for entering cell. It was concluded that internal CA was necessary to ‘trap’ the CO2 entering the cell and thus maintain a favorable CO2 gradient that permits its diffusive entry. Changes in the O2 evolution rate at inorganic carbon (Ci) concentration saturating for photosynthesis and on the photosynthetic conductance for Ci were found when external CA was inhibited. Based on these changes and the significant CA activity (ca. 9% of the total activity) found in nongreen membrane fraction, the presence of external CA associated with plasma membrane was postulated. The presence of CA associated with chloroplast membrane was also suggested. [ABSTRACT FROM AUTHOR]

Wild cherry (Prunus avium L.) shoots were cultured in closed vessels on a proliferation medium and the volatile substances released during incubation at photosynthetic photon flux density of 30 μmol m-2 s-1 were determined. Ethylene and CO2 started forming at the beginning of the incubation period an linear relationship between their formation was observed even at high CO2 concentrations. After 30 days of culture, CO2 reached a concentration of 30%. Shoots released ethanol and acetaldehyde after several days of incubation. [ABSTRACT FROM AUTHOR]

A procedure for the culture in vitro of isolated small berries of Vitis vinifera L. cv. Muscat of Alexandria in a Murasbige and Skoog basal medium supplemented with N6-benzyladenine and indoleacetic acid is described. Berries developed well in culture during 60 days and tripled in size, but remained green and smaller than normal berries grown in vivo. Some callus formed on the distal end of the berry, and where major skin damage occurred, callus emerged from the cracked berries. In order to examine their biosynthetic competency, berries which were previously cultured in vitro for 60 days were incubated for 48 h in a Murashige and Skoog medium containing a [14C]-labelled water-soluble fraction. This fraction was isolated from grape berries located adjacent to a leaf that had been exposed to gaseous 14CO2 in full sunlight for 5 h. The berries were then recultured for 48 h after which a glycosidic fraction was isolated on a C18 reversed phase column and further separated by thin layer chromatography (TLC). The major labelled band corresponded to the geranyl-,β-rutinoside marker, indicating that grape berries have the ability to synthesize monoterpene glycosides. This band also consisted of other monoterpene glycosides as revealed by the gas chromatography-mass spectrometry (GC-MS) analysis of their aglycones (released by enzymatic hydrolysis). [ABSTRACT FROM AUTHOR]

The evidence for and against photosynthetic CO2 fixation by guard cells is described and critically evaluated. There is a large body of literature on this subject, including enzyme activity assays, immunological assays for ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) in extracts, in situ immunological indicators at the light-and electron-microscope levels, products of 14CO2 fixation, and indirect indications such as the effect of light on the P-glycerate pool size, chlorophyll a (Chl a) flourescence transients, and alkalinization of medium. Although it is not possible to reconcile all the literature, I show that most reports indicate that the photosynthetic carbon-reduction pathway is absent in guard cells or, at most, does not exceed about 5% of that in mesophyll cells on a Chl basis. Because a mesophyll cell contains approximately 30 times more Chl than a guard cell does, the reported level of the pathway is equivalent to ?0.1 to 0.2% mesophyll contamination, of which it is difficult to ensure the absence. Even if present at these levels, the pathway would not contribute significantly to carbon metabolism. [ABSTRACT FROM AUTHOR]

Proliferating cultures of Actinidia deliciosa A. Chev., C. F. Liang and A. R. Ferguson cv. Tomuri (♂) were grown under photosynthetic photon flux density (PPFD) rates ranging from 30 to 250 μmol m-2 s-1 in order to determine certain physiological parameters in vitro: CO2 evolution, photosynthesis at three CO2 atmospheric concentrations (330, 1 450 and 4 500 μl l-1), fresh and dry matter accumulation and proliferation rate. A proportional response in dry weight, dry/fresh weight ratios and PPFD was found. The proliferation rate increased up to 120 μmol m-2 s-1 but decreased at higher rates. At the highest PPFD, the CO2, released from cultures and accumulated in the vessels reached 200 μl l-1; at the lowest rate the CO2 concentration reached 10 500 μl l-1 after 28 days of culture. The photosynthetic rate at 1 450 and 4 500 μl l-1 of CO2 was nearly 4 times higher than at the lowest concentration tested. [ABSTRACT FROM AUTHOR]

It was shown previously that the convexity (curvature or rate of bending) of the photosynthetic light response curve was strongly correlated with chlorophyll content in shade acclimated conifer needles (Leverenz 1987, Physiol. Plant. 71: 20-29), in agreement with an hypothesis that gradients of light within leaves affect the convexity. In the present study it is shown that the convexity at any given chlorophyll content can be altered when leaves of Pinus sylvestris L. Picea glauca (Muench), Picea mariana (M.II.) BS.P. and Picea abies (L.) Kant pre-treated with less shade. This probably induced a differential acclimation of cells on the top and bottom sides of the leaves to their local light environment. Leaves were illuminated on i) their top surface, ii) their bottom surface, or iii) uniformly in a light integrating sphere during measurements of photosynthesis. After shoots had been transferred from their growth environment to a new measuring environment, the convexity increased from the first to the second day towards a maximum of 0.97. The rate of increase towards this maximum was 55 to 62% per day and probably is the result of re-acclimation of cells within the leaves. The data shown that the act of measuring photosynthesis induces a significant alteration in the experimental material when measurements are made for more than one day. The convexity of the light response curve of photosynthesis, was independent of whether the steady state measurements were made beginning in the dark and sequentially increasing photon flux density or beginning at high light and sequentially lowering photon flux density. Neither variation of CO2 concentration from 35 to 200 Pa. nor of temperature from 5° to 32°C affected the convexity.

The oxygen requirement for stomatal opening in maize plants (Zea mays L. hybrid INRA 508) was studied at different CO2 concentrations and light intensities. In the absence of CO2, stomatal opening always required O2, but this requirement decreased with increasing light intensity. In darkness, the lowest O2 partial pressure needed to obtain a weak stomatal movement was about 54 Pa. This value was lowered to ca 10 Pa in light (320 μmol m-2 s-1. On the other hand, in the absence of O2, CO2 enabled stomatal opening to occur in the light, presumably due to the evolved photosynthetic O2. Thus, CO2, which generally reduced stomatal aperture, could induce stomatal movement in anoxia and light. The effect of CO2 on stomatal opening was closely dependent on O2 concentration and light intensity. Stomatal aperture appeared CO2-independent at an O2 partial pressure which was dependent on light intensity and was about 25 Pa at 320 μmol m-2 s-1. The presence of a plasmalemma oxidase, in addition to mitochondrial oxidase, might explain the differences in the O2 requirement at various light intensities. The possible involvement of such a system in relation to the effect of CO2 is discussed. [ABSTRACT FROM AUTHOR]

Low levels of carbon dioxide regulate ethylene synthesis and higher levels inhibit ethylene action, but the mechanism for these effects is not known. [ABSTRACT FROM AUTHOR]

In Zea mays L., Bryophylum laxiflorum Bak., Gossypium hirsutum L., Helianthus annuus L., Oryza sativa L. and Vigna radiata L., a pre-illumination in nitrogen causes transient stomatal opening upon returning the plant to darkness and normal air. in Zea rnays L. hybrid INRA 508, K+ and CI- fluctuations in the stomatal complex during this stomatal opening in darkness were similar to those observed during a light-induced opening in normal air. These results are consistent with a two-phase mechanism for stomatal opening: a light phase that may occur in the absence of oxygen and carbon dioxide, and a dark phase during which oxygen is necessary for ion accumulation and other mechanisms of osmotic adjustment. [ABSTRACT FROM AUTHOR]

Delayed luminescence was measured from samples of a synchronously growing cell culture of the unicellular green alga, Scenedesmus obtusiusculus Chod., every second hour during the 24 h cell cycle under a 15/9 h light/dark regime. Both high (air + 2.5% CO2) and low (0.03% CO2) CO2 conditions were used, Under high CO2 conditions, white light excitation induces formation of a late (maximum reached after 10-60 s) transient peak in delayed luminescence in cells sampled after 10-16 h in the cell cycle. During most of the cell cycle low CO2 conditions stimulate a late transient peak formation. Excitation with 700 nm light, but not with 680 nm light, induces a late transient peak in delayed luminescence under high CO2 conditions. The transient peak is more or less pronounced depending on the cell stage. The variations might be due to a changing capacity for light-induced state I/state II transitions during the cell cycle. It is assumed that the formation of a late transient peak in delayed luminescence is due to ATP hydrolyzation and is thus favoured by a high ATP/NADPH ratio. Hydrolyzation of ATP affects the transthylakoidal ΔpH, which regulates the reverse electron flow to the plastoquinone-pool and QA/QB thus affecting the decay kinetics of the delayed luminescence. [ABSTRACT FROM AUTHOR]

A green-pigmented callus of the moss, Sphagnum imbricatum Hornsch, ex. Russ., was induced and a chlorophyllous cell suspension culture was established using a modified Murashige and Skoog's medium without plant hormones. Cell growth in the light in the presence of glucose started after a short lag and was exponential for 12 days. The chlorophyll level was about 15 μg (mg cell dry weight)-1 and photosynthetic activity ca 20 to 50 μmol O2 (mg chlorophyll)-1h-1. Cell growth in the light was negligible in the absence of glucose under ordinary air, but photoautotrophic growth was possible under elevated CO2 concentrations. In the dark, the moss cells grew heterotrophically and continued to synthesize chlorophyll, although at a much reduced rate. The suspension-cultured cells redifferentiated protonemata and shoots when transferred to solid Knop's medium. In contrast to the callus cells, which could not assimilate nitrate, redifferentiated plantlets could use nitrate as the sole nitrogen source. [ABSTRACT FROM AUTHOR]

Maize plants (Zea mays L. hybrid INRA 508) were placed under controlled conditions of light and CO2 partial pressure. The K+, Cl− and P contents were then determined by X‐ray microanalysis in the bulbous end of guard cells and in the center of subsidiary cells. The results were interpreted in connection with the stomatal conductance at the time of sampling. In normal air, the K+ and Cl− contents in guard cells only rose from a light threshold of about 300 μmol m−2 s−1 at which stomata were already largely open. At 600 μmol m−2 s−1, the K+ and Cl− levels in guard cells attained values that were 3‐ and 8‐fold greater, respectively, than the values observed in darkness. The K+ and Cl− contents in the subsidiary cells remained quite constant irrespective of the light conditions. CO2‐free air in darkness induced a significant K+ influx towards guard and subsidiary cells. Under light and in CO2‐free air, the K+ and Cl− contents dramatically increased in the guard cells, but slightly decreased in the subsidiary cells. Thus, when subjected to strong light in CO2‐free air, the K+ and Cl− contents in the subsidiary cells were approximately equal to those measured in normal air conditions. In the guard cells, stomatal opening was associated with a marked shift of the Cl−/K+ ratio – from 0.3 for closed stomata to ca 1 for fully open stomata. This could imply a slow change in the nature of the principal counterion accompanying K+ during stomatal opening. The content of P in guard cells appeared, in contrast to that of K+ and Cl−, to be practically independent of stomatal aperture.

This review discusses (a) how the concentration of fructose 2,6-bisphosphate is controlled in spinach leaves, (b) how fructose 2,6-bisphosphate and cytosolic metabolites control the cytosolic fructose-1,6-bisphosphatase (EC 3.1.3.11), and (c) how the activities of the fructose-1,6-bisphosphatase and of sucrose phosphate synthase (EC 2.3.1.14) are coordinated. These features provide the elements of a fine control network that regulates sucrose synthesis during photosynthesis. The rate of sucrose synthesis is coordinated with the supply of photosynthate, so that concentrations of metabolites and phosphate are maintained at a level in the chloroplast which allows rapid CO2 fixation. The rate of sucrose synthesis can also be modified to alter the amount of photosynthate that remains in the chloroplast for conversion to starch.

When treated with ethylene in O2, conditioned potato (Solanum tuberosum L. cv. Russet Burbank) tubers – that is, tubers kept at room temperature for 10 days or more – yield slices that are CN− resistant. Ten % CO2 in the gas mixture not only synergizes the effect of ethylene, but replaces the need for conditioning as well. The response to CO2 is more pronounced with increasing time from harvest. By contrast fresh slices from untreated tubers are CN− sensitive, as are slices from tubers incubated in O2 or O2 plus CO2. The suggestion is made that CN− resistance is constitutive, and that treatment with ethylene/CO2 in O2 confers on potato tuber tissue a resistance to the extensive degradation of membrane phospholipids that normally attends slicing and leads to the loss of CN− resistance. In this connection respiration inhibition by imidazole, an inhibitor of fatty acid α‐oxidation, is extensive in slices of untreated tubers, and sharply diminished in slices of ethylene‐treated tubers in proportion to their CN− resistance. The coextensive rise of respiration rate and CN− resistance in aged potato slices has led to the presumption that the CN−‐resistant path mediates the respiration climax. Accordingly the alkaloid, lycorine, has been considered to inhibit the development of CN− resistance in aging potato slices because it curtails the wound‐induced respiration. A comparison was carried out on the effect of lycorine on CN−‐sensitive and CN−‐resistant fresh slices – the latter obtained from ethylene/CO2‐treated tubers. Lycorine suppressed the development of the wound‐induced respiration without restricting the development of CN− resistance.

The production of ethylene and carbon dioxide by Pinus radiata D. Don cotyledons cultured on shoot‐forming medium in sealed Erlenmeyer flasks was studied. To establish the role of these gases on morphogenesis three experimental approaches were used: (1) capping the flasks with serum caps on various days, and removing the serum caps at different stages of morphogenesis, (2) absorbing the gases by setting up traps singly and in combination during the various stages of differentiation and (3) incubating the cultures under continuous flow of constant gas mixtures. The results indicate that both ethylene and carbon dioxide, which build up during the first 10 to 15 days of culture, promote morphogenesis. Excessive accumulation after the initiation of buds causes some degree of dedifferentiation. When both the gases were eliminated from the flasks, bud formation and growth were inhibited. In the absence of oxygen, ethylene and carbon dioxide fail to influence growth and morphogenesis.

The presence of a living root of tomato (Lycopersicon esculentum Mill. cv. Panase F) had a strong positive effect on growth in vitro of hyphal fragments of Cantharellus cibarius Fr. This was observed for 12 out of 14 fungal strains tested. Initial re-growth of hyphae was independent of the presence of a root, but for the further development of strong mycelial growth 7 strains completely depended on the presence of a root. Five strains showed a considerably prolonged lag phase in the absence of a root and only 2 strains were independent. The presence of a root had no influence on the specific growth rates. Hyphal fragments of the totally root-dependent strain S1 grew strongly in the absence of a root if they were brought into intimate mutual contact. Factor(s) stimulating growth were apparently produced by both roots and fungus. Volatiles from donor cultures of tomato roots of C. cibarius, Boletus edulis, and Tylopilus felleus stimulated growth of hyphal fragments in root-less receiver cultures. This effect was prevented by the presence of a KOH solution. Donor cultures could be replaced by O.5% CO2. [ABSTRACT FROM AUTHOR]

A red background illumination synergistically increased the sensitivity of the stomatal conductance response to low intensity blue tight in wheat seedlings (Triticum aestivum cv, Starke II, Weibull). It also saturated the photosynthesis dependent mechanisms so that they did not respond to the low quantum fluence rates needed to activate the blue light mechanism. Thus dual beam experiments provide a suitable experimental approach to study the blue light mechanism for stomatal regulation in the intact leaf. Time course studies indicated that in short time experiments the enhancement effect of the red background light was primarily a result of the increase in conductance level rather than a direct effect of the red light. This was confirmed with experiments where the stomatal blue light response was enhanced due to partial stomatal opening in CO2 free air as well as due to circadian rhythm. During long term experiments the response to blue light gradually decreased. It could then, however, be restored by a simultaneous red background light. [ABSTRACT FROM AUTHOR]

Seasonal measurements of net CO2 assimilation, leaf conductance and mesophyll conductance were made in the field on mature, fruiting and defruited Prunus persica L. Batsch trees. During early stages of fruit growth there were no significant differences in leaf gas exchange characteristics between fruiting and defruited trees. During the early part of the last stage of fruit growth, CO2 assimilation rates were 11-15% higher in fruiting trees than defruited trees. These increased assimilation rates corresponded with approximately 30% increases in leaf conductance and only minor changes in mesophyll conductances or leaf CO2 assimilation capacity as indicated by leaf nitrogen content. It is concluded that under the field conditions of this study the. fruit effect on photosynthesis is primarily related to stomatal behavior, [ABSTRACT FROM AUTHOR]

In many species, including woody plants, most of the nitrate absorbed by roots is translocated in the xylem to leaves where it is either assimilated or stored in vacuoles. Some species, however, assimilate nitrate mainly in their roots, in leaves, reductant and ATP for nitrate assimilation are mainly derived from photosynthesis. Theoretical considerations suggest that leaf assimilation is energetically more efficient: than root assimilation when photosynthesis is light-saturated and competition between carbon dioxide and nitrate for photochemical energy is minimised. There may be mechanisms to minimise competition between carbon dioxide and nitrate assimilation.