Light dependence of quantum yields of Photosystem II and CO2 fixation in C3 and C4 plants

The light dependence of quantum yields of Photosystem II (_II) and of CO₂ fixation were determined in C₃ and C₄ plants under atmospheric conditions where photorespiration was minimal. Calculations were made of the apparent quantum yield for CO₂ fixation by dividing the measured rate of photosynthesis by the absorbed light [A/I=_CO2 and of the true quantum yield by dividing the estimated true rate of photosynthesis by absorbed light [(A+R_l)/I_a=_CO2·], where R_L is the rate of respiration in the light. The dependence of the _II/_CO2 and _II/_CO2 ^* ratios on light intensity was then evaluated. In both C₃ and C₄ plants there was little change in the ratio of _II/_CO2 at light intensities equivalent to 10–100% of full sunlight, whereas there was a dramatic increase in the ratio at lower light intensities. Changes in the ratio of _II/_CO2 can occur because respiratory losses are not accounted for, due to changes in the partitioning of energy between photosystems or changes in the relationship between PS II activity and CO₂ fixation. The apparent decrease in efficiency of utilization of energy derived from PS II for CO₂ fixation under low light intensity may be due to respiratory loss of CO₂. Using dark respiration as an estimate of R_L, the calculated _II/_CO2 ^* ratio was nearly constant from full sunlight down to approx 5% of full sunlight, which suggests a strong linkage between the true rate of CO₂ fixation and PS II activity under varying light intensity. Measurements of photosynthesis rates and _II were made by illuminating upper versus lower leaf surfaces of representative C₃ and C₄ monocots and dicots. With the monocots, the rate of photosynthesis and the ratio of _II/_CO2 exhibited a very similar patterns with leaves illuminated from the adaxial versus the abaxial surface, which may be due to uniformity in anatomy and lack of differences in light acclimation between the two surfaces. With dicots, the abaxial surface had both lower rates of photosynthesis and lower _II values than the adaxial surface which may be due to differences in anatomy (spongy versus palisade mesophyll cells) and/or light acclimation between the two surfaces. However, in each species the response of _II/_CO2 to varying light intensity was similar between the two surfaces, indicating a comparable linkage between PS II activity and CO₂ fixation.Abbreviations A measured rate of CO₂ assimilation - A+R_L true rate of CO₂ assimilation; e - CO₂ estimate of electrons transported through PSII per CO₂ fixed by RuBP carboxylase - f fraction of light absorbed by Photosystem II - F'_m yield of PSII chlorophyll fluorescence due to a saturating flash of white light under steady-state photosynthesis - F_s variable yield of fluorescence under steady-state photosynthesis; PPFD-photosynthetic photon flux density - I_a absorbed PPFD - PS II Photosystem II - R_d rate of respiration in the dark - R_I rate of respiration in the light estimated from measurement of R_d or from analysis of quantum yields - apparent quantum yield of CO₂ assimilation under a given condition (A/absorbed PPFD) - true quantum yield of CO₂ assimilation under a given condition [(A+R_L)/(absorbed PPFD)] - quantum yield for photosynthetic O₂ evolution - electrons transported via PS II per quantum absorbed by PS II Supported by USDA Competitive Grant 90-37280-5706.     

Carbon-isotope discrimination by leaves of Flaveria species exhibiting different amounts of C3-and C4-cycle co-function

Carbon-isotope ratios were examined as ¹³C values in several C₃, C₄, and C₃–C₄ Flaveria species, and compared to predicted ¹³C, values generated from theoretical models. The measured ¹³C values were within 4 of those predicted from the models. The models were used to identify factors that contribute to C₃-like ¹³C values in C₃–C₄ species that exhibit considerable C₄-cycle activity. Two of the factors contributing to C₃-like ¹³C values are high CO₂ leakiness from the C₄ pathway and pi/pa values that were higher than C₄ congeners. A marked break occurred in the relationship between the percentage of atmospheric CO₂ assimilated through the C₄ cycle and the ¹³C value. Below 50% C₄-cycle assimialtion there was no significant relationship between the variables, but above 50% the ¹³C values became less negative. These results demonstrate that the level of C₄-cycle expression can increase from, 0 to 50% with little integration of carbon transfer from the C₄ to the C₃ cycle. As expression increaces above 50%, however, increased integration of C₃- and C₄-cycle co-function occurs.Abbreviations and symbols RuBP carboxylase ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) - PEP carboxylase phosphoenolpyruvate carboxylase (EC 4.1.1.31) - pa atmospheric CO₂ partial pressure - pi intercellular CO₂ partial pressure - isotope ratio - quantum yield for CO₂ uptake     

The Use of the [13C]/[12C] Ratio for the Assay of the Microbial Oxidation of Hydrocarbons

The study deals with a comparative analysis of the relative abundances of the carbon isotopes ¹²C and ¹³C in the metabolites and biomass of the Burkholderia sp. BS3702 and Pseudomonas putida BS202-p strains capable of utilizing aliphatic (n-hexadecane) and aromatic (naphthalene) hydrocarbons as sources of carbon and energy. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of Burkholderia sp. BS3702 on n-hexadecane (¹³C = –44.6 ± 0.2) were characterized by the values of ¹³C_{CO 2} = –50.2 ± 0.4, ¹³C_biom = –46.6 ± 0.4, and ¹³C_exo = –41.5 ± 0.4, respectively. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of the same bacterial strain on naphthalene (¹³C = –21 ± 0.4) were characterized by the isotope effects ¹³C_{CO 2} = –24.1 ± 0.4, ¹³C_biom = –19.2 ± 0.4, and ¹³C_exo = –19.1 ± 0.4, respectively. The possibility of using the isotope composition of metabolic carbon dioxide for the rapid monitoring of the microbial degradation of petroleum hydrocarbons in the environment is discussed.     

Mechanisms for controlling balance between light input and utilisation in the salt tolerant alga Dunaliella C9AA

The yield of photosynthetic O₂ evolution was measured in cultures of Dunaliella C9AA over a range of light intensities, and a range of low temperatures at constant light intensity. Changes in the rate of charge separation at Photosystem I (PS I) and Photosystem II (PS II) were estimated by the parameters _{PS I} and _{PS II} . _{PS I} is calculated on the basis of the proportion of centres in the correct redox state for charge separation to occur, as measured spectrophotometrically. _{PS II} is calculated using chlorophyll fluorescence to estimate the proportion of centres in the correct redox state, and also to estimate limitations in excitation delivery to reaction centres. With both increasing light intensity and decreasing temperature it was found that O₂ evolution decreased more than predicted by either _{PS I} or _{PS II}. The results are interpreted as evidence of non-assimilatory electron flow; either linear whole chain, or cyclic around each photosystem.Abbreviations F₀ dark level of chlorophyll fluorescence yield (PS II centres open) - F_m maximum level of chlorophyll fluorescence yield (PS II centres closed) - F_v variable fluorescence (F_m-F₀) - PS I Photosystem I - PS II Photosystem II - P₇₀₀ reaction centre chlorophyll(s) of PS I - q_N coefficient of non-photochemical quenching of chlorophyll fluorescence - q_P coefficient of photochemical quenching of fluorescence yield - q_E high-energy-state quenching coefficient - _{PS I} yield of PS I - _{PS II} yield of PS II - _S yield of photosynthetic O₂ evolution - _P intrinsic yield of open PS II centres     

Temporal variability in <Superscript>13</Superscript>C of respired CO<Subscript>2</Subscript> in a pine and a hardwood forest subject to similar climatic conditions

Temporal variability in the ¹³C of foliage (¹³C_F), soil (¹³C_S) and ecosystem (¹³C_R) respired CO₂ was contrasted between a 17.2-m tall evenly aged loblolly pine forest and a 35-m tall unevenly aged mature second growth mixed broadleaf deciduous forest in North Carolina, USA, over a 2-year period. The two forests are located at the Duke Forest within a kilometer of each other and are subject to identical climate and have similar soil types. The ¹³C_F, collected just prior to dawn, was primarily controlled by the time-lagged vapor pressure deficit (VPD) in both stands; it was used for calculating the ratio of intercellular to ambient CO₂ (Ci/Ca). A remarkable similarity was observed in the relationship between Ci/Ca and time-lagged VPD in these two forests despite large differences in hydraulic characteristics. This similarity emerged as a result of physiological adjustments that compensated for differences in plant hydraulic characteristics, as predicted by a recently proposed equilibrium hypothesis, and has implications to ecophysiological models. We found that in the broadleaf forest, the ¹³C of forest floor CO₂ efflux dominated the ¹³C_R, while in the younger pine forest, the ¹³C of foliage respired CO₂ dominated ¹³C_R. This dependence resulted in a more variable ¹³C_R in the pine forest when compared to the broadleaf forest due to the larger photosynthetic contribution. Given the sensitivity of the atmospheric inversion models to ¹³C_R, the results demonstrate that these models could be improved by accounting for stand characteristics, in addition to previously recognized effects of moisture availability, when estimating ¹³C_R.     

Short-term variations in δ<Superscript>13</Superscript>C of ecosystem respiration reveals link between assimilation and respiration in a deciduous forest

We present a comprehensive dataset of hourly, daily, and monthly measurements of carbon isotope measurements of CO₂ in canopy air from a temperate deciduous forest with the aim to identify the relevance of short-term variations in the isotopic signature of ecosystem respiration (¹³C_R) and to understand its underlying physiological processes. We show that during daytime low vertical mixing inside the canopy can lead to decoupling of the air in the lower and upper canopy layer resulting in large spatial variation of ¹³C in CO₂ of canopy air. Intercept of Keeling Plots also showed large temporal variation (3.8) over the course of the day demonstrating that intercepts can differ between day and night and suggesting that choosing the right time for sampling is essential to capture the isotopic signature of ecosystem respiration (¹³C_R). ¹³C_R as obtained from night-time measurements showed large variation of up to 2.65 on a day-to-day basis, which was similar to the observed variation of ¹³C_R over the seasonal cycle (3.08). This highlights the importance of short-term physiological processes within ecosystems for the isotopic composition of CO₂ in the atmosphere, not reflected by bulk plant and soil organic samples. At daily and monthly time scales, ¹³C_R increased with increasing ratio of vapour pressure deficit to photosynthetically active radiation, measured 4–5 days before. This suggests that ecosystem respiration was isotopically linked to assimilation. Furthermore, assimilates recently fixed in the canopy seem to form a labile carbon pool with a short mean residence time that is respired back to the atmosphere after 4–5 days.     

Hydrogen-isotope composition of leaf water in C3 and C4 plants: its relationship to the hydrogen-isotope composition of dry matter

The natural abundance hydrogen-isotope composition of leaf water ( ) and leaf organic matter ( _D ^org ) was measured in leaves of C₃ and C₄ dicotyledons and monocotyledons. The value of leaf water showed a marked diurnal variation, greatest enrichment being observed about midday. However, this variation was greater in the more slowly transpiring C₄ plants than in C₃ plants under comparable environmental conditions. A model based on analogies with a constant feed pan of evaporating water was developed and the difference between C₃ and C₄ plants expressed in terms of either differences in kinetic enrichment or different leaf morphology. Microclimatic and morphological features of the leaves which may be associated with this factor are discussed. There was no daily excursion in the _D ^org value in leaves of either C₃ or C₄ plants. When _D ^org values were referenced to the mean values during the period of active photosynthesis, the discrimination against deuterium during photosynthetic metabolism (D) was greater in C₃ plants (-117 to -121) than in C₄ plants (-86 to -109).These results show that the different water use strategies of C₃ and C₄ plants are responsible for the measured difference in deuterium-isotope composition of leaf water. However, it is unlikely that these physical processes account fully for the differences in hydrogen-isotope composition of the products of C₃ and C₄ photosynthetic metabolism.Symbols Hydrogen-isotope composition of leaf water - _D ^org hydrogen-isotope composition of leaf organic matter     

Effects of ganglioside GM1 on the thermotropic behavior of cholera toxin B subunit

Summary The B, or binding, subunit of cholera enterotoxin forms a pentameric ring structure in the intact toxin, and also when the subunit is isolated from the A subunit. The thermal denaturation of the B subunit ring was examined by differential scanning calorimetry in the presence and absence of ganglioside G_M1, its natural receptor. In the absence of ganglioside an irreversible endotherm was observed with maximal excess apparent heat capacity, C_max, at 74.6° C. When the ganglioside was added in increasing amounts, multiple transitions were observed at higher temperatures, the most prominent having a C_max at 90.8° C. At high ganglioside concentrations, the 74.6° C transition was not observed. In addition to the thermodynamic results a model is proposed for the interaction of G_M1 and B subunit pentamer. This model is derived independently of the calorimetric results (but is consistent with such data) and is based upon considerations of the geometry of the G_M1 micelle-B subunit pentamer.Abbreviations M_r molecular weight in daltons - G_M1 H³Neu-AcGgOse₄Cer^* = Gall 3Ga1NAc1 4Gal-[3 - 2NeuAc]1 4Glc1 1Cer (asterisked form follows the recommendations of the IUPACIUB Commission on Biochemical Nomenclature, Ref. 3) - R molar ratio of G_M1 to B monomer - DSC differential scanning calorimetry - C_max excess apparent heat capacity - C_max maximal value of C_ex - t_m temperature (° C) at C_ex = C_max - t_1/2 peak width in °C at C_ex = C_max/2 - H_cal calorimetric enthalpy - C _p ^d van't Hoff enthalpy - C _p ^d change in specific heat accompanying denaturation     

Quantifying Protein Folding Transition States with ΦT

A number of reaction coordinates have been proposed for reduced-dimensionalityrepresentations of a protein's folding free energy surface. We discuss in detail the entropic reaction coordinate _T = SS, recently introduced to quantify the conservation of mutations and the location of the folding transition state based on experimental temperature-tuning data. Numerical simulations illustrate the advantages as well as the limitations of _T. _T can be determined from experiment,computation, and analytical theory; _T can also be used to investigate structurally localized perturbations of the free energy surface. However, _T is only a relative reaction cordinate; furthermore, proteins undergo cold denaturation at sufficiently low temperatures, and care must be taken ininterpreting _T near the region where G/T = 0, particularly if the heat capacity change upon folding is small.     

Analogues of NADP+ as inhibitors and coenzymes for NADP+ malic enzyme from maize leaves

Structural analogues of the NADP⁺ were studied as potential coenzymes and inhibitors for NADP⁺ dependent malic enzyme from Zea mays L. leaves. Results showed that 1, N⁶-etheno-nicotinamide adenine dinucleotide phosphate ( NADP⁺), 3-acetylpyridine-adenine dinucleotide phosphate (APADP⁺), nicotinamide-hypoxanthine dinucleotide phosphate (NHDP⁺) and -nicotinamide adenine dinucleotide 2: 3-cyclic monophosphate (23NADPc⁺) act as alternate coenzymes for the enzyme and that there is little variation in the values of the Michaelis constants and only a threefold variation in V_max for the five nucleotides. On the other hand, thionicotinamide-adenine dinucleotide phosphate (SNADP⁺), 3-aminopyridine-adenine dinucleotide phosphate (AADP⁺), adenosine 2-monophosphate (2AMP) and adenosine 2: 3-cyclic monophosphate (23AMPc) were competitive inhibitors with respect to NADP⁺, while -nicotinamide adenine dinucleotide 3-phosphate (3NADP⁺), NAD⁺, adenosine 3-monophosphate (3AMP), adenosine 2: 5-cyclic monophosphate (25AMPc), 5AMP, 5ADP, 5ATP and adenosine act as non-competitive inhibitors. These results, together with results of semiempirical self-consistent field-molecular orbitals calculations, suggest that the 2-phosphate group is crucial for the nucleotide binding to the enzyme, whereas the charge density on the C₄ atom of the pyridine ring is the major factor that governs the coenzyme activity.Abbreviations NADP⁺ 1, N⁶-etheno-nicotinamide adenine dinucleotide phosphate - NHDP⁺ nicotinamide-hypoxanthine dinucleotide phosphate - APADP⁺ 3-acetylpyridine-adenine dinucleotide phosphate - SNADP⁺ thionicotinamide-adenine dinucleotide phosphate - AADP⁺ 3-aminopyridine-adenine dinucleotide phosphate - 23NADPc⁺ -nicotinamide adenine dinucleotide 2: 3-cyclic monophosphate - 3NADP⁺ -nicotinamide adenine dinucleotide 3-phosphate - 2AMP adenosine 2-monophosphate - 3AMP adenosine 3-monophosphate - 23AMPc adenosine 2: 3 monophosphate cyclic - A adenosine - RuBP ribulose 1,5-bisphosphate - SCF-MO Self-Consistent Field-Molecular Orbitals (method)     

Keeling plots for hummingbirds: a method to estimate carbon isotope ratios of respired CO<Subscript>2</Subscript> in small vertebrates

The carbon isotope composition of an animals breath reveals the composition of the nutrients that it catabolizes for energy. Here we describe the use of Keeling plots, a method widely applied in ecosystem ecology, to measure the ¹³C of respired CO₂ of small vertebrates. We measured the ¹³C of Rufous Hummingbirds (Selasphorus rufus) in the laboratory and of Mourning (Zenaida macroura) and White-winged (Z. asiatica) Doves in the field. In the laboratory, when hummingbirds were fed a sucrose based C3 diet, the ¹³C of respired CO₂ was not significantly different from that of their diet (¹³C_{C3 diet}). The ¹³C of respired CO₂ for C3 fasted birds was slightly, albeit significantly, depleted in ¹³C relative to ¹³C_{C3 diet}. Six hours after birds were shifted to a sucrose based C4 diet, the isotopic composition of their breath revealed that birds were catabolizing a mixture of nutrients derived from both the C3 and the C4 diet. In the field, the ¹³C of respired CO₂ from Mourning and White-winged Doves reflected that of their diets: the CAM saguaro cactus (Carnegeia gigantea) and C3 seeds, respectively. Keeling plots are an easy, effective and inexpensive method to measure ¹³C of respired CO₂ in the lab and the field.     

The use of 1JCαHα coupling constants as a probe for protein backbone conformation

Summary Simple pseudo-3D modifications to the constant-time HSQC and HCACO experiments are described that allow accurate (±0.5 Hz) measurement of one bond J_CH coupling constants in proteins that are uniformly enriched with ¹³C. An empirical ,-surface is calculated which describes the deviation of ¹J_CH from its random coil value, using 203 ¹J_CH values measured for residues in the proteins calmodulin, staphylococcal nuclease, and basic pancreatic trypsin inhibitor, for which and are know with good precision from previous X-ray crystallographic studies. Residues in -helical conformation exhibit positive deviations of 4–5 Hz, whereas deviations in -sheet are small and, on average, slightly negative. Data indicate that ¹J_CH depends primarily on , and that ¹J_CH may be useful as a qualitative probe for secondary structure. Comparison of ¹J_CH coupling constants measured in free calmodulin and in its complex with a 26-aminoacid peptide fragment of myosin light-chain kinase confirm that the calmodulin secondary structure is retained upon complexation but that disruption of the middle part of the central helix is even more extensive than in free calmodulin. Supplementary material available from the authors: One table listing 352 ¹J_CH and ¹J-values, together with ,-values for 203 residues of known conformation. Two figures showing (a) a Ramachandran plot of the ,-values of 203 residues used in deriving ¹J(,), and (b) the r.m.s.d. ¹J(,) distribution.     

Comparative water-use efficiency of Sporobolus arabicus and Leptochloa fusca and its relation with carbon-isotope discrimination under semi-arid conditions

Water-use efficiency (WUE) of Leptochloa fusca (L.) Kunth (Kallar grass) and Sporobolus arabicus Boiss. was determined under different soil moisture regimes. Plants grown in lysimeters were subjected to three soil moisture regimes, viz. well-watered (100%), medium-watered (75%), and low-watered (50%) of total available water (TAW). The soil moisture was restored on alternate days by adding the required volume of water on the basis of neutron moisture meter readings taken from neutron access tubes installed in each lysimeter. The grasses were harvested after suitable intervals (4 months) to obtain maximum biomass. Leaf samples collected at each harvest were analyzed for carbon-isotope discrimination (¹³C) with an isotope ratio (¹³C/¹²C) mass spectrometer. Results indicated significant differences in WUE of both grasses subjected to different water regimes. Sporobolus arabicus showed higher WUE than Kallar grass. However, Kallar grass showed better value of yield response factor (k _y = 0.649) compared with Sporobolus (k _y = 1.06) over the entire season. The data confirm that these grasses can be grown successfully in water-limited environments by selecting an optimum soil moisture level for maximum biomass production. The mean carbon-isotope discrimination (¹³C) of Kallar grass (–14.4) and Sporobolus (–12.8) confirm that both are C₄ plants. The carbon-isotope discrimination () was significantly and negatively correlated with WUE of the two species studied. The results of the present study confirm that ¹³C or of leaves can be used as good predictor of WUE in some C₄ plants.     

The effect of fumonisin B1 on developing chick embryos: correlation between de novo sphingolipid biosynthesis and gross morphological changes

Fumonisins, mycotoxins produced byFusarium moniliforme and a number of other fungi, are potent inhibitors of the sphinganine-N-acyltransferase, a key enzyme of sphingolipid biosynthesis, and cause neuronal degeneration, liver and renal toxicity, cancer and other injury to animals.In this study we investigated the effect of fumonisin B₁ on the sphingolipids of developing chick embryos. After yolk sac injection of fumonisin B₁ a concentration and time dependent increase of the sphinganine-over-sphingosine ratio of the embryos could be demonstrated. Studies were done to evaluate the effect of fumonisin B₁ on the glycosphingolipid pattern of the chick embryos. In the presence of 72 µg fumonisin B₁ per egg the incorporation of [¹⁴C]galactose and of [¹⁴C]serine into embryonic glycosphingolipids was reduced by about 70%, although the mass of glycosphingolipids was not affected by the toxin. However, a reduction of the wet weight of the treated embryos was observed. Additionally, histological examinations of whole embryo sections of control and fumonisin B₁ treated embryos are presented. Fumonisin B₁ caused haemorrhages under the skin as well as in the liver of treated embyros. A close correlation between disruption of sphingoid metabolism and light microscopic detectable tissue lesions could be observed.Abbreviations Cer ceramide (N-acylsphingosine) - FB₁ fumonisin B₁ - GM3 NeuAc23Gal14Glc11Cer - GD3 NeuAc28NeuAc23Gal14Glc11Cer - GD1a NeuAc23Gal13GalNAc14(NeuAc23)Gal14Glc11Cer - GT1b NeuAc23Gal13GalNAc14(NeuAc28NeuAc23) Gal14Glc11Cer - HPLC high pressure liquid chromatography - PBS phosphate buffered saline - PDMP 1-phenyl-2-dodecanoylamino-3-morpholino-1-propanol - Sa sphinganine - So sphingosine - Sa/So sphinganine-over-sphingosine - TLC thin layer chromatography - Tris Tris(hydroxymethyl)aminomethan Dedicated to Dr Sen-itiroh Hakomori in celebration of his 65th birthday.     

Stable carbon and oxygen isotopic compositions of recent charophyte oosporangia and water from Malham Tarn,U.K.: palaeontological implications

Charophyte oosporangia and water samples from a highly calcareous lake were measured for stable carbon and oxygen isotopic composition. The time period over which the oosporangia calcify is short, thus any biochemical relationship between the water and oosporangia"s calcite represents only one time window (late Summer in Malham Tam). This important temporal restraint must also apply to interpretations of all fossil material measured. The ¹⁸O_c of the charophyte oosporangia is deduced to be in equilibrium with the ¹⁸O of the water for a given temperature. The ¹³ C_c of the charophyte oosporangia was approximately 2.5 per mil lower than the ¹³C_DIC in the water we measured. With the release Of CO₂ with phosphoric acid from the charophyte oosporangia, there was no significant difference in the ¹⁸O_c values obtained, regardless of whether or not the carbonate was separated from the organic center, however ¹³C_c values were marginally lower for carbonate plus organic center measurements. Our results indicate that fossil charophyte gyrogonites can be used to elucidate the geochemistry of the ancient water body in which they lived.     

Photosynthetic Pathway Types in Rangeland Plant Species from Inner Mongolia,North China

Photosynthetic pathway types, based on ¹³C measurements, were determined for 125 species in 95 genera and 32 families growing in rangelands from Inner Mongolia. Of the total species, 4 species from 3 genera and 2 families had C₄ photosynthesis (2 species in Gramineae and 2 in Chenopodiaceae) and 118 species from 90 genera and 31 families had C₃ photosynthesis. The number of C₄ species differed significantly among four rangeland sites, 4 species in desert, 3 species in steppe, but no C₄ species were identified in meadow and dune. Six species [e.g. Agriophyllum arenarium Bieb., Bassia dasyphylla O. Kuntze, Saussurea japonica (Thunb.) DC.] earlier identified as C₄ species using the enzyme ratio method were found as C₃ species using the carbon isotope ratios (¹³C). Hence the enzyme ratio method for C₃ and C₄ identification may not always be reliable. The ¹³C values of 3 species of Crassulaceae, which had been considered as CAM species, differed remarkably [–25.79 for Sedum aizoon L., –24.42 for Osostachys fimbriatus (Turcz.) Berger, and –16.97 for O. malacophyllus (Pall.) Fisch], suggesting that the use of ¹³C method as a diagnosis for CAM photosynthetic pathway type may not always be reliable and supplementary measurements are needed.     

Effect of size on the energy acquired in species of the fish from a neotropical reservoir,Brazil

In this paper we analysed autotrophic sources of the carbon ( ¹³C) and the trophic position ( ¹⁵N) of Leporinus friderici in the influence area of Corumbá Reservoir, Brazil. We collected samples of muscles of fish from different sizes riparian vegetation, C₄ grasses, zooplankton, periphyton and particulate organic carbon (POC). There were significant differences for the carbon isotope proportion found in muscles of L.friderici in the different size groups analysed. The highest values of ¹³C recorded for middle sized individuals is attributed to the large contribution of C₄ plants in their diet. Small individuals sampled upstream also receive similar contribution from C₄ plants. In contrast the same size group sampled downstream from the reservoir, has a much smaller of C₄ plants. The ¹³C negative character of small individuals from downstream is due to the larger contribution of C₃ plants (except periphyton). At larger sizes we found intermediate ¹³C values. The ¹⁵N proportions we found for each size group were not significantly different, however we found decreasing mean values with increasing size. The trophic level calculated from the dietary data was higher than that found with the ¹³C concentration in the muscle, except for small individuals, when the values were equal.     

Preparation and heteronuclear 2D NMR spectroscopy of a DNA dodecamer containing a thymidine residue with a uniformly 13C-labeled deoxyribose ring

Summary [¹³C₅]-2-Deoxy-d-ribose, synthesized from [¹³C₆]-d-glucose (98% ¹³C), was coupled with thymine to give [1,2,3,4,5-¹³C₅]-thymidine (T) in an 18% overall yield. The thymidine was converted to the 3-phosphoramidite derivative and was then incorporated into a dodecamer 5-d(CGCGAATTCGCG)-3 by solid-phase DNA synthesis. Preparation of 0.24 mole of the labeled dodecamer, which is sufficient for a single NMR sample, consumed only 25 mg of glucose. By virtue of the ¹³C labels, all of the ¹H-¹H vicinal coupling constants in the sugar moieties were accurately determined by HCCH-E.COSY.     

Host factor requirements and some properties of ΦXtB

Summary Replication of XtB, a capsid mutant of bacteriophage X174, depends on the host functions directed by the E. coli genes dnaE, dnaF, dnaG, dnaZ, lig and rep. The cellular products of dnaA, dnaB, dnaC(D), dnaI, dnaP, polA, polB and xth genes are, however, dispensable for the viral growth. In these host factor requirements, XtB resembles phages K and St-1, rather than X174. Host ranges of XtB, St-1 and K overlap considerably, and growth temperature of the three phages is somewhat higher than that of X174. Furthermore, XtB is, like K, inactivated by antiserum against St-1. XtB may thus fill an evolutionary gap between the X174 group and the St-1 group.