Growth, photosynthesis, nitrogen partitioning and responses to CO2 enrichment in a barley mutant lacking NADH-dependent nitrate reductase activity

Plant growth, photosynthesis and leaf constituents were examined in the wild-type (WT) and mutant nar1 of barley (Hordeum vulgare L. cv. Steptoe) that contains a defective structural gene encoding NADH-dependent nitrate reductase (NADH-NAR). In controlled environment experiments, total biomass, rates of photosynthesis, stomatal conductance, intercellular CO(2) concentrations and foliar non-structural carbohydrate levels were unchanged or differed slightly in the mutant compared with the WT. Both genotypes displayed accelerated plant growth rates when the CO(2) partial pressure was increased from 36 to 98 Pa. Total NADH-NAR activity was 90% lower in the mutant than in the WT, and this was further decreased by CO(2) enrichment in both genotypes. Inorganic nitrate was greater in the mutant than in the WT, whereas in situ nitrate assimilation by excised leaves was two-fold greater for the WT than for the mutant. Foliar ammonia was 50% lower in the mutant than in the WT under ambient CO(2). Ammonia levels in the WT were decreased by about one-half by CO(2) enrichment, whereas ammonia was unaffected by elevated CO(2) in mutant leaves. Total soluble amino acid concentrations in WT and mutant plants grown in the ambient CO(2) treatment were 30.1 and 28.4 micromol g(-1) FW, respectively, when measured at the onset of the light period. Seven of the twelve individual amino acids reported here increased during the first 12 h of light in the ambient CO(2) treatment, leading to a doubling of total soluble amino acids in the WT. The most striking effect of the mutation was to eliminate increases of glutamine, aspartate and alanine during the latter half of the photoperiod in the ambient CO(2) treatment. Growth in elevated CO(2) decreased levels of total soluble amino acids on a diurnal basis in the WT but not in mutant barley leaves. The above results indicated that a defect in NADH-NAR primarily affected nitrogenous leaf constituents in barley. Also, we did not observe synergistic effects of CO(2) enrichment and decreased foliar NADH-NAR activity on most N-containing compounds.     

Analysis of (1-13C)leucine and (13C)KIC in plasma by capillary gas chromatography/mass spectrometry in protein turnover studies

The methods used for the determination of the concentration and isotope enrichment of (1-13C)leucine and its metabolite (13C) alpha-ketoisocaproic acid (KIC) in plasma for the study of whole-body protein turnover are described. Leucine was analysed as its N-heptafluorobutyryl isobutyl ester and KIC as its quinoxalinol-TMS derivative, both by chemical ionization selected ion monitoring gas chromatography/mass spectrometry (GC/MS). The sensitivity of the leucine assay was improved 30 times by monitoring the negative ions under the conditions described. The coefficient of variation for enrichment and concentration measurements were 0.5% and 2%, respectively, with a minimum detectable enrichment of 0.1 at% excess for both assays.     

Response of respiration of soybean leaves grown at ambient and elevated carbon dioxide concentrations to day-to-day variation in light and temperature under field conditions

BACKGROUND AND AIMS: Respiration is an important component of plant carbon balance, but it remains uncertain how respiration will respond to increases in atmospheric carbon dioxide concentration, and there are few measurements of respiration for crop plants grown at elevated [CO(2)] under field conditions. The hypothesis that respiration of leaves of soybeans grown at elevated [CO(2)] is increased is tested; and the effects of photosynthesis and acclimation to temperature examined. METHODS: Net rates of carbon dioxide exchange were recorded every 10 min, 24 h per day for mature upper canopy leaves of soybeans grown in field plots at the current ambient [CO(2)] and at ambient plus 350 micromol mol(-1) [CO(2)] in open top chambers. Measurements were made on pairs of leaves from both [CO(2)] treatments on a total of 16 d during the middle of the growing seasons of two years. KEY RESULTS: Elevated [CO(2)] increased daytime net carbon dioxide fixation rates per unit of leaf area by an average of 48 %, but had no effect on night-time respiration expressed per unit of area, which averaged 53 mmol m(-2) d(-1) (1.4 micromol m(-2) s(-1)) for both the ambient and elevated [CO(2)] treatments. Leaf dry mass per unit of area was increased on average by 23 % by elevated [CO(2)], and respiration per unit of mass was significantly lower at elevated [CO(2)]. Respiration increased by a factor of 2.5 between 18 and 26 degrees C average night temperature, for both [CO(2)] treatments. CONCLUSIONS: These results do not support predictions that elevated [CO(2)] would increase respiration per unit of area by increasing photosynthesis or by increasing leaf mass per unit of area, nor the idea that acclimation of respiration to temperature would be rapid enough to make dark respiration insensitive to variation in temperature between nights.     

In vivo regulation of phenylalanine hydroxylation to tyrosine, studied using enrichment in apoB-100

Phenylalanine hydroxylation is necessary for the conversion of phenylalanine to tyrosine and disposal of excess phenylalanine. Studies of in vivo regulation of phenylalanine hydroxylation suffer from the lack of a method to determine intrahepatocyte enrichment of phenylalanine and tyrosine. apoB-100, a hepatic export protein, is synthesized from intrahepatocyte amino acids. We designed an in vivo multi-isotope study, [(15)N]phenylalanine and [2H2]tyrosine to determine rates of phenylalanine hydroxylation from plasma enrichments in free amino acids and apoB-100. For independent verification of apoB-100 as a reflection of enrichment in the intrahepatocyte pool, [1-(13)C]lysine was used as an indicator amino acid (IAA) to measure in vivo changes in protein synthesis in response to tyrosine supplementation. Adult men (n = 6) were fed an amino acid-based diet with low phenylalanine (9 mg.kg(-1).day(-1), 4.54 mumol.kg(-1).,h(-1)) and seven graded intakes of tyrosine from 2.5 (deficient) to 12.5 (excess) mg.kg(-1).day(-1). Gas chromatography-quadrupole mass spectrometry did not detect any tracer in apoB-100 tyrosine. A new and more sensitive method to measure label enrichment in proteins using isotope ratio mass spectrometry demonstrated that phenylalanine hydroxylation measured in apoB-100 decreased linearly in response to increasing tyrosine intake and reached a break point at 6.8 mg.kg(-1).day(-1). IAA oxidation decreased with increased tyrosine intake and reached a break point at 6.0 mg.kg(-1).day(-1). We conclude: apoB-100 is an accurate and useful measure of changes in phenylalanine hydroxylation; the synthesis of tyrosine via phenylalanine hydroxylation is regulated to meet the needs for protein synthesis; and that plasma phenylalanine does not reflect changes in protein synthesis.     

温室CO2施肥对黄瓜幼苗根系生长及分泌物和伤流液组成的影响

为探讨温室蔬菜CO2施肥的根际效应,以黄瓜幼苗为试材,研究了CO2施肥(上午施肥/上、下午施肥;施肥浓度/对照浓度(950±50)/(350±50)μmol/molCO2)对根系生长及分泌物和伤流液组成的影响。结果表明,CO2施肥明显促进黄瓜幼苗根系发育,根系生物量显著增加;单株根系分泌物中氨基酸、糖、有机酸和酚酸总量增加,但单位鲜重根系分泌量却呈现增幅减少、无变化甚至降低趋势,说明单株分泌量增加主要由根系生长量的增加所引起。CO2施肥促进幼苗对养分的吸收,伤流液中矿质元素、ZT浓度增加,但GA、ABA和IAA浓度降低;与上午CO2施肥相比,上、下午均CO2施肥的效果更明显。CO2施肥促进了黄瓜幼苗根系发育及其代谢活性,为地上部的旺盛生长创造了条件。     

A new measurement technique reveals rapid post-illumination changes in the carbon isotope composition of leaf-respired CO2

We describe an open leaf gas exchange system coupled to a tunable diode laser (TDL) spectroscopy system enabling measurement of the leaf respiratory CO(2) flux and its associated carbon isotope composition (delta(13)C(Rl)) every 3 min. The precision of delta(13)C(Rl) measurement is comparable to that of traditional mass spectrometry techniques. delta(13)C(Rl) from castor bean (Ricinus communis L.) leaves tended to be positively related to the ratio of CO(2) produced to O(2) consumed [respiratory quotient (RQ)] after 24-48 h of prolonged darkness, in support of existing models. Further, the apparent fractionation between respiratory substrates and respired CO(2) within 1-8 h after the start of the dark period was similar to previous observations. In subsequent experiments, R. communis plants were grown under variable water availability to provide a range in delta(13)C of recently fixed carbohydrate. In leaves exposed to high light levels prior to the start of the dark period, CO(2) respired by leaves was up to 11 per thousand more enriched than phloem sap sugars within the first 10-15 min after plants had been moved from the light into the dark. The (13)C enrichment in respired CO(2) then decreased rapidly to within 3-7 per thousand of phloem sap after 30-60 min in the dark. This strong enrichment was not observed if light levels were low prior to the start of the dark period. Measurements of RQ confirmed that carbohydrates were the likely respiratory substrate for plants (RQ > 0.8) within the first 60 min after illumination. The strong (13)C enrichment that followed a high light-to-dark transition coincided with high respiration rates, suggesting that so-called light-enhanced dark respiration (LEDR) is fed by (13)C-enriched metabolites.     

Effects of positive end-expiratory pressure on hepatic blood flow and performance

Positive end-expiratory pressure (PEEP) may impair extrapulmonary organ function. However, the effects of PEEP on the liver are unclear. We tested the hypothesis that at a constant cardiac output (CO), PEEP does not induce changes in hepatic blood flow (QL) and parenchymal performance. In splenectomized, close-chested canine preparations (group I, n = 6), QL was derived as hepatic outflow using electromagnetic flow probes (QLemf), and hepatic performance was defined by extraction and clearance of indocyanine green (ICG). In a noninvasive model (group II, n = 7), the effects of PEEP on hepatic performance alone were similarly analyzed. Measurements were taken during intermittent positive-pressure ventilation (IPPV1), after addition of 10 cmH2O PEEP to IPPV (PEEP1), during continued PEEP but after return of CO to IPPV1 levels by intravascular volume infusions (PEEP2), and after removal of both PEEP and excess blood volume (IPPV2). Phasic inspiratory decreases in QLemf present during positive-pressure ventilation were not increased during either PEEP1 or PEEP2. Mean QLemf decreased proportionately with CO during PEEP1 (P less than 0.05), but was restored to IPPV1 levels in a parallel fashion with CO during PEEP2. The ICG pharmacokinetic responses to PEEP were complex, with differential effects on extraction and clearance. Despite this, hepatic performance was not imparied in either group. we conclude that global QL reductions during PEEP are proportional to PEEP-induced decreases in CO and are preventable by returning CO to pre-PEEP levels by intravascular volume infusions. However, covarying changes in blood volume and hepatic outflow resistance may independently modulate hepatic function.     

Effects of increased atmospheric CO2 and N supply on photosynthesis, growth and cell composition of the cyanobacterium Spirulina platensis (Arthrospira)

The consequences of the addition of CO2 (1%) in cultures of S. platensis are examined in terms of biomass yield, cell composition and external medium composition. CO2 enrichment was tested under nitrogen saturating and nitrogen limiting conditions. Increasing CO2 levels did not cause any change in maximum growth rate while it decreased maximum biomass yield. Protein and pigments were decreased and carbohydrate increased by high CO2, but the capability to store carbohydrates was saturated. C:N ratio remained unchanged while organic carbon released to the external medium was enhanced, suggesting that organic carbon release in S. platensis is an efficient mechanism for the maintenance of the metabolic integrity, balancing the cell C:N ratio in response to environmental CO2 changes. CO2 affected the pigment content: Phycocyanin, chlorophyll and carotenoids were reduced in around 50%, but the photosynthetic parameters were slightly changed. We propose that in S. platensis CO2 could act promoting degradation of pigments synthetised in excess in normal CO2 conditions, that are not necessary for light harvesting. Nitrogen assimilation was significantly not affected by CO2, and it is proposed that the inability to stimulate N assimilation by CO2 enrichment determined the lack of response in maximum growth rate. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of endurance training on excessive CO2 expiration due to lactate production in exercise

We attempted to determine the change in total excess volume of CO2 output (CO2 excess) due to bicarbonate buffering of lactic acid produced in exercise due to endurance training for approximately 2 months and to assess the relationship between the changes of CO2 excess and distance-running performance. Six male endurance runners, aged 19-22 years, were subjects. Maximal oxygen uptake (VO2max), oxygen uptake (VO2) at anaerobic threshold (AT), CO2 excess and blood lactate concentration were measured during incremental exercise on a cycle ergometer and 12-min exhausting running performance (12-min ERP) was also measured on the track before and after endurance training. The absolute magnitudes in the improvement due to training for CO2 excess per unit of body mass per unit of blood lactate accumulation (delta la-) in exercise (CO2 excess.mass-1.delta la-), 12-min ERP, VO2 at AT (AT-VO2) and VO2max on average were 0.8 ml.kg-1.l-1.mmol-1, 97.8 m, 4.4 ml.kg-1. min-1 and 7.3 ml.kg-1.min-1, respectively. The percentage change in CO2 excess.mass-1.delta la- (15.7%) was almost same as those of VO2max (13.7%) and AT-VO2 (13.2%). It was found to be a high correlation between the absolute amount of change in CO2 excess.mass-1.delta la-, and the absolute amount of change in AT-VO2 (r = 0.94, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of isotope ratio (IR) mass spectrometry for the study of drug metabolism

Isotope ratio (IR) mass spectrometry was evaluated for the study of drug metabolism and balance using 13C, 15N2-labelled antipyrine (AP) as a test drug. Rats were given 40 mg kg-1 (13C,15N2)AP intraperitoneally. Breath, urine, faeces and blood were collected. Except for breath, samples were combusted in sealed quartz tubes. The resulting CO2 and N2 were analysed for excess 13C and 15N, relative to pre-dose samples, by IR mass spectrometry. In addition, blood levels of AP and cumulative excretion of urinary AP metabolites were determined by gas chromatography/mass spectrometry/selected ion monitoring (GC/MS/SIM) and high-performance liquid chromatography (HPLC) respectively. Excess 13C and 15N levels in blood were comparable with observed levels of AP, and urinary recoveries of 13C (42%) were in good agreement with those calculated from HPLC data (45%). N-Demethylation, one of the important pathways of AP metabolism, was most rapidly determined by excess 13CO2 excretion in breath (8%). The IR mass spectral analysis complemented gas chromatographic/mass spectrum and HPLC analyses, and was less complex.     

CO(2) enrichment enhances flag leaf senescence in barley due to greater grain nitrogen sink capacity

Senescence is a highly regulated process which is under genetic control. In monocarpic plants, the onset of fruit development is the most important factor initiating the senescence process. During senescence, a large fraction of plant nutrients is reallocated away from vegetative tissues into generative tissues. Senescence may therefore be regarded as a highly effective salvage mechanism to save nutrients for the offspring. CO(2) enrichment, besides increasing growth and yield of C(3) plants, has often been shown to accelerate leaf senescence. C(3) plants grown under elevated CO(2) experience alterations in their nutrient relations. In particular their tissue nitrogen concentrations are always lower after exposure to elevated CO(2). We used a monocarpic C(3) crop - spring barley (Hordeum vulgare cv. Alexis) - grown in open-top field chambers to test the effects of CO(2) enrichment on growth and yield, on nitrogen acquisition and redistribution, and on the senescence process in flag leaves, at two applications of nitrogen fertilizer. CO(2) enrichment (650 vs. 366 μmol mol(-1)) caused an increase both in biomass and in grain yield by 38% (average of the two fertilizer applications) which was due to increased tillering. Total nitrogen uptake of the crops was not affected by CO(2) treatment but responded solely to the N supply. Nitrogen concentrations in grains and straw were significantly lower (-33 and -24%) in plants grown at elevated CO(2). Phenological development was not altered by CO(2) until anthesis. However, progress of flag leaf senescence as assessed by chlorophyll content, protein content and content of large and small subunit of RubisCO and of cytochrome b559 was enhanced under elevated CO(2) concentrations by approximately 4 days. We postulate that CO(2) enhanced flag leaf senescence in barley crops by increasing the nitrogen sink capacity of the grains.     

Pulmonary diffusing capacities for nitric oxide and carbon monoxide determined by rebreathing in dogs

Pulmonary diffusing capacities (DL) of NO and CO were determined simultaneously from rebreathing equilibration kinetics in anesthetized paralyzed supine dogs (mean body wt 20 kg) after denitrogenation (replacement of N2 by Ar). During rebreathing the dogs were ventilated in closed circuit with a gas mixture containing 0.06% NO, 0.06% 13C18O, and 1% He in Ar for 15 s, with tidal volume of 0.5 liter and frequency of 60/min. The partial pressures of NO, 13C18O, 16O18O, N2, Ar, CO2, and He in the trachea were continuously analyzed by mass spectrometry. Measurements were performed at various O2 levels characterized by the mean end-expired PO2 during rebreathing (PE'O2). In control conditions ("normoxia," PE'O2 = 67 +/- 8 Torr) the following mean +/- SD values were obtained (in ml.min-1.Torr-1): DLNO = 52.4 +/- 11.0 and DLCO = 15.4 +/- 2.9. In hypoxia (PE'O2 = 24 +/- 7 Torr) DLNO increased by 11 +/- 8% and DLCO by 19 +/- 10%, and in hyperoxia (PE'O2 = 390 +/- 26 Torr) DLNO decreased to 87 +/- 3% and DLCO to 56 +/- 8% with respect to values in normoxia. DLNO/DLCO of 3.24 +/- 0.06 (hypoxia), 3.38 +/- 0.31 (normoxia), and 5.54 +/- 1.04 (hyperoxia) were significantly higher than the NO/CO Krogh diffusion constant ratio (1.92) predicted for simple diffusion through aqueous layers. With increasing O2 uptake elicited by 2,4-dinitrophenol, DLNO and DLCO increased and DLNO/DLCO remained close to unchanged. The results suggest that the combined effects of diffusion and chemical reaction with hemoglobin limit alveolar-capillary transport of CO. If it is assumed that reaction kinetics of NO with hemoglobin (known to be extremely fast) are not rate limiting for NO uptake, the contribution of the slow chemical reaction with hemoglobin to the total CO uptake resistance (= 1/DLCO) was estimated to be 38% in hypoxia, 41% in normoxia, and 64% in hyperoxia. The various factors expected to restrict the validity of this analysis are discussed, in particular the effects of functional inhomogeneity.     

Synergistic interactions of CO2 enrichment and nitrogen deposition promote growth and ecophysiological advantages of invading Eupatorium adenophorum in Southwest China

Global environmental change and ongoing biological invasions are the two prominent ecological issues threatening biodiversity worldwide, and investigations of their interaction will aid to predict plant invasions and inform better management strategies in the future. In this study, invasive Eupatorium adenophorum and native congener E. stoechadosmum were compared at ambient and elevated atmospheric carbon dioxide (CO(2)) concentrations combined with three levels of nitrogen (N; reduced, control and increased) in terms of growth, energy gain, and cost. Compared with E. stoechadosmum, E. adenophorum adopted a quicker-return energy-use strategy, i.e. higher photosynthetic energy-use efficiency and shorter payback time. Lower leaf mass per area may be a pivotal trait for the invader, which contributed to an increased N allocation to Rubisco at the expense of cell walls and therefore to higher photosynthetic energy gain. CO(2) enrichment and N deposition synergistically promoted plant growth and influenced some related ecophysiological traits, and the synergistic effects were greater for the invader than for the native congener. Reducing N availability by applying sugar eliminated the advantages of the invader over its native congener at both CO(2) levels. Our results indicate that CO(2) enrichment and N deposition may exacerbate E. adenophorum's invasion in the future, and manipulating environmental resources such as N availability may be a feasible tool for managing invasion impacts of E. adenophorum.     

Compensation for PSII photoinactivation by regulated non-photochemical dissipation influences the impact of photoinactivation on electron transport and CO2 assimilation

The extent to which PSII photoinactivation affects electron transport (PhiPSII) and CO2 assimilation remains controversial, in part because it frequently occurs alongside inactivation of other components of photosynthesis, such as PSI. By manipulating conditions (darkness versus low light) after a high light/low temperature treatment, we examined the influence of different levels of PSII inactivation at the same level of PSI inactivation on PhiPSII and CO2 assimilation for Arabidopsis. Furthermore, we compared PhiPSII at high light and optimum temperature for wild-type Arabidopsis and a mutant (npq4-1) with impaired capacities for energy dissipation. Levels of PSII inactivation typical of natural conditions (< 50%) were not associated with decreases in PhiPSII and CO2 assimilation at photon flux densities (PFDs) above 150 micromol m(-2) s(-1). At higher PFDs, the light energy being absorbed was in excess of the energy that could be utilized by downstream processes. Arabidopsis plants downregulate PSII activity to dissipate such excess in accordance with the level of PSII photoinactivation that also serves to dissipate absorbed energy. Therefore, the overall levels of non-photochemical dissipation and the efficiency of photochemistry were not affected by PSII inactivation at high PFD. Under low PFD conditions, such compensation is not necessary, because the amount of light energy absorbed is not in excess of that needed for photochemistry, and inactive PSII complexes are dissipating energy. We conclude that moderate photoinactivation of PSII complexes will only affect plant performance when periods of high PFD are followed by periods of low PFD.     

Ethoxyzolamide Differentially Inhibits CO2 Uptake and Na+-Independent and Na+-Dependent HCO3- Uptake in the Cyanobacterium Synechococcus sp. UTEX 625

The effects of ethoxyzolamide (EZ), a carbonic anhydrase inhibitor, on the active CO2 and Na+-independent and Na+-dependent HCO3- transport systems of the unicellular cyanobacterium Synechococcus sp. UTEX 625 were examined. Measurements of transport and accumulation using radiochemical, fluorometric, and mass spectrometric assays indicated that active CO2 transport and active Na+-independent HCO3- transport were inhibited by EZ. However, Na+-independent HCO3- transport was about 1 order of magnitude more sensitive to EZ inhibition than was CO2 transport (50% inhibition = 12 [mu]M versus 80 [mu]M). The data suggest that both the active CO2 (G.D. Price, M.R. Badger [1989] Plant Physiol 89: 37-43) and the Na+ -independent HCO3 - transport systems possessed carbonic anhydrase-like activity as part of their mechanism of action. In contrast, Na+-dependent HCO3- transport was only partially (50% inhibition = 230 [mu]M) and noncompetitively inhibited by EZ. The collective evidence suggested that EZ inhibition of Na+ -dependent HCO3- transport was an indirect consequence of the action of EZ on the CO2 transport system, rather than a direct effect on HCO3- transport. A model is presented in which the core of the inorganic carbon translocating system is formed by Na+-dependent HCO3- transport and the CO2 transport system. It is argued that the Na+-independent HCO3 - utilizing system was not directly involved in translocation, but converted HCO3- to CO2 for use in CO2 transport.     

干旱和CO2浓度升高对干旱区春小麦气孔密度及分布的影响

 通过对不同土壤水分状况、不同CO2浓度条件下春小麦叶片气孔的观测结果表明：干旱和CO2浓度升高不仅影响叶片气孔密度,而且也影响其分布。随干旱程度的加剧,气孔密度有明显的上升趋势,气孔在叶片上的分布趋向均匀;随CO2浓度的升高,气孔密度有明显的下降趋势,其分布也趋向均匀。水分状况和CO2浓度相同时,气孔密度及分布受不同温度的影响。     

The combined effects of CO2 concentration and solar UV-B radiation on faba bean grown in open-top chambers

The response of faba bean seedlings to the combined effects of increased atmospheric CO2 concentrations ([CO2]) and solar UV-B irradiance was studied using open-top chambers transparent to UV-B radiation. The purpose of the study was to determine whether effects of increased [CO2] on growth and physiology are modified by the present solar UV-B fluence rate in the Netherlands. Seedlings were exposed to 350 or 700 micromoles mol-1 CO2. At both [CO2], solar UV-B irradiance was either present or reduced using polyester foil opaque to UV-B radiation. To obtain information on the time dependence of increased [CO2] and UV-B radiation effects, three harvests were performed during the experiment. CO2 enrichment resulted in increased biomass production at all harvests. At the final harvest, UV-B radiation did not affect biomass production but a significant decrease was observed after 14 d of treatment. A reduction of the UV-B fluence increased shoot length at both [CO2] throughout the experiment. UV-B radiation slightly altered biomass allocation. Plants grown at reduced levels of UV-B radiation invested less biomass in flowers and more in stem material compared to plants grown at ambient UV-B levels. CO2 enrichment resulted in a stimulation of net photosynthesis after 26 and 38 d of treatment. UV-B reduction did not alter this response. After 26 d of treatment, photosynthetic acclimation to CO2 enrichment was observed, which was probably the result of accumulation of carbohydrates in the leaves. After 38 d, photosynthetic acclimation was no longer present. The UV absorbance of methanolic leaf extracts was increased by CO2 enrichment only. Both CO2 enrichment and solar UV-B reduced the transmittance of radiation through intact attached leaves. Interaction between [CO2] and UV-B radiation was limited to UV-A transmittance of leaves. Under prevalent experimental conditions, UV-B radiation did not affect the measured physiological parameters. Most open-top chambers used for climate change research are constructed of materials which do not transmit UV-B radiation. Our results indicate that part of the 'chamber effects' on plant height often described in the literature might be explained by the absence of solar UV-B radiation in these chambers.     

Annual and seasonal variation of sap flow and conductance of pine trees grown in elevated carbon dioxide and temperature

Measurements of sap flow, crown structure, and microclimate were used to estimate the transpiration of individual 30-year-old Pinus sylvestris L. trees grown in elevated temperature and CO2. The trees were enclosed in closed-top chambers and exposed either to current ambient conditions (CON), or elevated CO2 (+350 micromol mol(-1); EC), or elevated temperature (+2 to +6 degrees C; ET) or a combination of EC and ET (ECT) since 1996, and the measurements were made from 1999 to 2001. EC significantly increased annual sap flow per tree (Ft.m) by 14% in 1999, but reduced it by 13% in 2000 and 16% in 2001. The CO2-induced increase in Ft.m in 1999 was due to a large increase in foliage area of trees, which more than compensated for a small decrease in crown conductance (Gc). The CO2-induced decreases in Ft.m in 2000 and 2001 resulted from a pronounced decline in Gc, which was much greater than the increase in foliage area. The CO2-induced increase in sensitivity of Gc at high vapour pressure deficit (VPD) did not alter the general response of sap flow to CO2 enrichment, but it did affect the diurnal courses of sap flow on some days during the main growing season (days 150-240). ET increased Ft.m by 53%, 45%, and 57% in 1999, 2000, and 2001, respectively, attributable to the combined effects of greater foliage area and maximum crown conductance, lower stomatal sensitivity to high VPD, and higher transpiration demand relative to the control treatments. There was no significant interaction between CO2 and temperature on sap flow, because ECT entailed approximately similar patterns of sap flow to ET, suggesting that the temperature played a dominate role in the case of ECT under boreal climate conditions.     

The purification and some equilibrium properties of the nitrite reductase of the bacterium Wolinella succinogenes.

The bacterium Wolinella succinogenes produces a nitrite reductase enzyme that can be purified to homogeneity in high yield by a combination of detergent extraction, hydroxyapatite chromatography and Mr fractionation. Nitrite reductase activity is found to be present in both a high- and a low-Mr fraction. The high-Mr fraction has been shown to consist of the low-Mr nitrite reductase enzyme associated with a hydrophobic 'binding protein'. The amino acid composition for both proteins is reported. The nitrite reductase enzyme shows spectral characteristics indicative of the presence of c-type haem groups. Measurements at 610 nm indicate the presence of some high-spin haem groups at neutral pH. This haem subgroup undergoes a pH-linked high-spin - low-spin transition at alkaline pH. Approximately two of the six haem groups present within the enzyme bind CO with low affinity (KD = 0.4 mM). The enzyme also shows a range of redox activities with various inorganic reagents. The enzyme has been shown to exhibit dithionite reductase, oxygen reductase and CO2 reductase activities.     

Photoautotrophic culture of Coffea arabusta somatic embryos: photosynthetic ability and growth of different stage embryos

Coffea arabusta somatic embryos were cultured and development of stomata, rate of CO2 fixation or production, chlorophyll content and chlorophyll fluorescence were studied in embryos at different stages of development. Cotyledonary and germinated embryos have photosynthetic capacity, although pretreatment at a high photosynthetic photon flux (PPF) (100 micromol m(-2) s(-1)) for 14 d increased photosynthetic ability. Except in a very small number of cases, stomata did not develop fully in precotyledonary stage embryos and were absent in torpedo stage embryos. Low chlorophyll content (90-130 microg g(-1) fresh mass) was noted in torpedo and precotyledonary stage embryos compared with cotyledonary and germinated embryos (300-500 microg g(-1) fresh mass). Due to the absence of stomata and low chlorophyll content in the torpedo and precotyledonary stage embryos, the photosynthetic rate was low and, in some cases, CO2 production was observed. These data suggest that the cotyledonary stage is the earliest stage that can be cultured photoautotrophically to ensure plantlet development. When grown photoautotrophically (in a sugar-free medium with CO2 enrichment in the culture headspace and high photosynthetic photon flux), torpedo and precotyledonary stage embryos lost 20-25% of their initial dry mass after 60 d of culture. However, in cotyledonary and germinated embryos, the dry mass of each embryo increased by 10 and 50%, respectively. By using a porous supporting material, growth (especially root growth) was increased in cotyledonary stage embryos. In addition, photoautotrophic conditions, high PPF (100-150 micromol m(-2) s(-1)) and increased CO2 concentration (1100 micromol mol(-1)) were found to be necessary for the development of plantlets from cotyledonary stage embryos.