Share of carbohydrates in the humus substances composition

The effect of different concentrations of hydrochloric acid on the qualitative an quantitative content of carbohydrates in humus fraction hydrolyzates was investigated. Three humic acid preparations were subjected to the usual procedure for obtaining fractions of humic and hymatomelanic acids. The carbohydrate content of the hydrolyzates was determined after their Chromatographic separation on Whatman 1, using the Partridge system and detection with acid anilin phtalate. The results showed that the qualitative carbohydrate content in the hydrolyzates of most humus fractions of samples used was identical. With increasing acid concentrations the amount of hydrolyzable carbohydrates usually increased, the total amount of carbohydrate in the hydrolyzate not exceeding 4% . The difference in the carbohydrate content as between hydrolysis with 0-9N and 5-3N HC1 was sometimes fourfold. A higher content of hexoses than of pentoses was generally found.     

Behavioural responses of fathead minnows to carbohydrates found in aquatic environments

Carbohydrates make up a significant portion of dissolved organic carbon in waterways. Apart from studies demonstrating that chondroitin causes avoidance behaviours in some fish species, no work has been done to determine how fish respond to carbohydrates commonly found in their environment. In this study fathead minnows (Pimephales promelas) were attracted to N-acetyl-d -glucosamine, avoided d -arabinose and had no response to either d -xylose or d -glucose using a behavioural assay. This study provides further evidence that carbohydrates may be important chemosensory cues for fish.     

Contribution of Azolla filiculoides to hydrazine elimination from water

Wetlands Ecology and Management - In this research we report the significant effect of the floating water fern Azolla filiculoides on the elimination of hydrazine (N2H4) from water, which is a...     

Thiyl radicals abstract hydrogen atoms from carbohydrates: reactivity and selectivity.

Free radical damage of DNA is a well-known process affecting biological tissue under conditions of oxidative stress. Though carbohydrate-derived radicals are generally "repaired" by hydrogen transfer from thiols, the reverse possibility, namely hydrogen abstraction by thiyl radicals from carbohydrates, exists. The biological relevance of this process has been discussed controversially, especially because of the lack of rate constants. Therefore, we have measured rate constants for the hydrogen transfer reaction between thiyl radicals from cysteine and selected carbohydrates, 2-deoxy-D-ribose (dRib), 2-deoxy-D-glucose (dGls), alpha-D-glucose (Gls), and inositol (Ino). Rate constants are on the order of 10(4) M(-1)s(-1), with the highest average value for dRib, (2.7 +/- 1.0) x 10(4) M(-1)s(-1), and the lowest average value for dGls, (1.6 +/- 0.2) x 10(4) M(-1)s(-1), based on two ways of kinetic analysis, standard competition kinetics and stochastic simulation of the experimental results, respectively. In general, thiyl radicals attack preferentially the C(1)-H bond of the carbohydrates, to an extent of ca. 72% in dRib and 90% in dGls. Kinetic measurements were possible through a specifically designed competition system measuring the reaction of thiyl radicals with either the C-H bonds of the carbohydrates or the C(alpha)-H bond of cysteine under conditions where the extent of other competitive reactions of the thiyl radicals were minimized.     

Separation of carbohydrates and carbohydrate derivatives by HPLC with cation-exchange columns at high pH

Cation-exchange columns were found to be stable when used at high pH and high temperature for high-performance liquid chromatographic separations of carbohydrates and carbohydrate derivatives. Pulsed amperometric detection and refractive index detection were found to be suitable detection modes with these cation-exchange columns. Significant differences in carbohydrate separation selectivity were observed between cation-exchange and anion-exchange columns.     

C4 photosynthetic modifications in the evolutionary transition from land to water in aquatic grasses

Cladistic analysis supports the conclusion that the Orcuttieae tribe of C₄ grasses reflect evolution from a terrestrial ancestry into seasonal pools. All nine species in the tribe exhibit adaptations to the aquatic environment, evident in the structural characteristics of the juvenile foliage, which persist submerged for 1–3 months prior to metamorphosis to the terrestrial foliage. Aquatic leaves of the least derived or basal genus Neostapfia have few morphological and anatomical characteristics specialized to the aquatic environment and have retained full expression of the C₄ pathway, including Kranz anatomy. Orcuttia species have many derived characteristics and are more specialized to the aquatic environment. These latter species germinate earlier in the season and persist in the submerged stage longer than Neostapfia and evidence from the literature indicates length of submergence is positively correlated with fitness components. Aquatic leaves of Orcuttia species lack Kranz or PCR bundle sheath anatomy, yet ¹⁴C-pulse chase studies indicate >95% malate + aspartate as the initial products of photosynthesis and these products turn over rapidly to phosphorylated sugars, indicating a tight coupling of the C₄ and C₃ cycles. Presence of the C₄ pathway is further supported by enzymological data. Contemporary dogma that Kranz anatomy is a sine qua non for operation of the C₄ pathway is contradicted by the patterns in Orcuttia; however, it is unknown whether the pathway acts as a CO₂ concentrating mechanism in these aquatic plants. Received: 12 June 1997 / Accepted: 10 February 1997     

Modification of kanamycin-esculin-azide agar to improve selectivity in the enumeration of fecal streptococci from water samples.

Kanamycin-esculin-azide agar was modified by increasing the concentration of sodium azide to 0.4 g liter-1 and replacing kanamycin sulfate with 5 mg of oxolinic acid liter-1. The modification, named oxolinic acid-esculin-azide (OAA) agar, was compared with Slanetz-Bartley and KF agars by using drinking water and seawater samples. The OAA agar showed higher specificity, selectivity, and recovery efficiencies than those obtained by using the other media. In addition, no confirmation of typical colonies was needed when OAA agar was used, which significantly shortens the time of sample processing and increases the accuracy of the method.     

小麦非结构性碳水化合物分配对水分胁迫的生理响应

以‘西旱2号’小麦为试材,采用水分胁迫和复水处理方法,研究了小麦发育过程中不同水分胁迫下非结构性碳水化合物(NSC)在小麦旗叶、茎、叶鞘等器官中的动态变化,以及籽粒中碳代谢相关酶(可溶性淀粉合成酶SSS和淀粉粒结合态合成酶GBSS)活性的变化.结果表明:不同程度水分胁迫对小麦旗叶、茎、叶鞘等器官中蔗糖含量无显著影响.随水分胁迫的深入,花后12～ 18 d旗叶中淀粉含量显著增加;水分胁迫缩短了花后茎和叶鞘中淀粉的积累时间,抑制了茎中淀粉的转化和分配;而叶鞘中淀粉的积累逐渐增大,在中度水分胁迫下积累提前终止.在水分胁迫初期,各营养器官中的NSC含量为旗叶＞茎＞叶鞘;随着水分胁迫的深入,各营养器官中的NSC含量为茎＞旗叶＞叶鞘.小麦主要营养器官中NSC的分配速率及主要代谢酶的变化可能是小麦对水分胁迫的一种生理调节反应.     

Contribution from the chirality of the growing chain to the enantiomer selectivity in activated-NCA polymerization of α-amino acid N-carboxyanhydride

As a model compound for the growing chain in the activated-NCA type of polymerization of α-amino acid N-carboxyanhydride (NCA), 3-[ω-acetylglycyl-poly(α-amino acid) acyl]-α-amino acid NCA (called the prepolymer) having various degrees of polymerization (DPs) was synthesized by the polymerization of Phe, Val, Glu(OEt), and Asp(OBzl) NCA in the presence of AcGly NCA by the tertiary amine. Activated (S)-Phe, Val, Glu(OEt), and Asp(OBzl) NCA were added to the terminal cyclic group of the corresponding (S)- or (R)- prepolymer, and the enantiomer selectivity in the reaction was investigated. With prepolymers having DPs ranging from 1 to 15, the addition reaction always took place preferentially between species having the same configuration, and the degree of the enantiomer selection increased with increasing DP of the prepolymer. With prepolymers having DP = 1 and 2, we found contributions from the chiral terminal unit and the chiral penultimate unit to the enantiomer selection, respectively. Prepolymer having DP = 5 was shown to take a β-type conformation, which led to higher enantiomer selection; and prepolymers having DP = 10 and 15 were shown to take an α-helix conformation, which led to much higher enantiomer selection than did the β-type conformation. In the present investigation the mechanisms of terminal-unit control, penultimate-unit control and conformational control of the enantiomer selection in the activated-NCA type of polymerization were clearly observed.     

Contribution of residues in second transmembrane domain of ASIC1a protein to ion selectivity

Acid-sensing ion channels (ASICs) are proton-gated cation-selective channels expressed in the peripheral and central nervous systems. The ion permeation pathway of ASIC1a is defined by residues 426–450 in the second transmembrane (TM2) segment. The gate, formed by the intersection of the TM2 segments, localizes near the extracellular boundary of the plasma membrane. We explored the contribution to ion permeation and selectivity of residues in the TM2 segment of ASIC1a. Studies of accessibility with positively charged methanethiosulfonate reagents suggest that the permeation pathway in the open state constricts below the gate, restricting the passage to large ions. Substitution of residues in the intracellular vestibule at positions 437, 438, 443, or 446 significantly increased the permeability to K⁺ versus Na⁺. ASIC1a shows a selectivity sequence for alkali metals of Na⁺>Li⁺>K⁺≫Rb⁺>Cs⁺. Alanine and cysteine substitutions at position 438 increased, to different extents, the relative permeability to Li⁺, K⁺, Rb⁺, and Cs⁺. For these mutants, ion permeation was not a function of the diameter of the nonhydrated ion, suggesting that Gly-438 encompasses an ion coordination site that is essential for ion selectivity. M437C and A443C mutants showed slightly increased permeability to K⁺, Rb⁺, and Cs⁺, suggesting that substitutions at these positions influence ion discrimination by altering molecular sieving. Our results indicate that ion selectivity is accomplished by the contribution of multiple sites in the pore of ASIC1a.     

The relationship of brown humus to lignin

Summary A fraction of organic matter called brown humus was studied in relation to plant lignins. Infrared analysis, methoxy content, and presence of certain phenolic groups showed that this material contains a lignin structure. Decomposition of corn roots showed that one of the first parts of the lignin molecule to be decomposed is by the loss of methoxy groups probably from 2,6-dimethoxyphenol part of the molecule. Studies withP. ochro chloron. Showed two transformations occurred in the decomposition of the lignin molecule: — (1) A demethylation and (2) a formation of carbonyl groups.     

Unusual diel pHs in water as related to aquatic vegetation

High diel pHs (% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabmiwayaara% aaaa!36E2!\[\bar X\] > 9.0) showing little or no fluctuation were observed in several impoundments. This phenomenon was experimentally produced in water that contained only Myriophyllum spicatum or species of filamentous algae. Diel pHs ⩾ 9.0 were produced in the laboratory with as little as 0.2 g/1 of algae or vascular plants. The ability of these plants to cause high diel pHs in water may have evolved in response to competition with phytoplankton for carbon.     

Uranium accumulation by aquatic plants from uranium-contaminated water in Central Portugal

Several species of plants have developed a tolerance to metal that enables them to survive in metal contaminated and polluted sites. Some of these aquatic plants have been reported to accumulate significant amounts of specific trace elements and are, therefore, useful for phytofiltration. This work focuses the potential of aquatic plants for the phytofiltration of uranium (U) from contaminated water. We observed that Callitriche stagnalis, Lemna minor, and Fontinalis antipyretica, which grow in the uraniferous geochemical province of Central Portugal, have been able to accumulate significant amounts of U. The highest concentration of U was found in Callitriche stagnalis (1948.41 mg/kg DW), Fontinalis antipyretica (234.79 mg/kg DW), and Lemna minor (52.98 mg/kg DW). These results indicate their potential for the phytofiltration of U through constructed treatment wetlands or by introducing these plants into natural water bodies in the uraniferous province of Central Portugal.     

Contribution of solvent water to the solution X-ray scattering profile of proteins

A theoretical framework is presented to analyze how solvent water contributes to the X-ray scattering profile of protein solution. Molecular dynamics simulations were carried out on pure water and an aqueous solution of myoglobin to determine the spatial distribution of water molecules in each of them. Their solution X-ray scattering (SXS) profiles were numerically evaluated with obtained atomic-coordinate data. It is shown that two kinds of contributions from solvent water must be considered to predict the SXS profile of a solution accurately. One is the excluded solvent scattering originating in exclusion of water molecules from the space occupied by solutes. The other is the hydration effect resulting from formation of a specific distribution of water around solutes. Explicit consideration of only two molecular layers of water is practically enough to incorporate the hydration effect. Care should be given to using an approximation in which an averaged electron density distribution is assumed for the structure factor because it may predict profiles considerably deviating from the correct profile at large K.