TEMPERATURE-DEPENDENT DEGRADATION OF SOIL ORGANIC MATTER IN FARMLANDS AND PASTURES.

To determine the rates of soil organic matter degradation in farmlands and pastures and their temperature dependency, soil samples collected in Aomori, Japan, were sieved and incubated at different temperatures (10, 20 and 30°C) for 700 d, with amounts of respired CO2 being measured during the incubation period. Results were analysed using a three-compartment model (active, intermediate and resistant compartment), and the decomposition rates of the two labile compartments were approximated using an exponential decay function. The Arrhenius equation was applied to the decay function rate constant to obtain rate constants at the examined temperatures. The estimated degradation rate constants of the most active compartment in pasture soil were more sensitive to temperature than the corresponding value in farmland. The seasonal changes in rate constants were consistent with each soil temperature. At both fields, it is estimated that the degradation of soil organic matter occurred from April to October.

RETENTION OF ORGANICALLY BOUND DEUTERIUM IN GRASS PLANTS EXPOSED TO HEAVY WATER VAPOUR AT DIFFERENT GROWTH STAGES.

Potted timothy grass plants were exposed to heavy water (HDO) vapour at seven different periods during the third growth of harvestable shoots (the part 5-cm above the ground surface), and the concentration of non-exchangeable organically bound deuterium (NE-OBD) was measured in harvestable shoots, stubbles and roots at the third harvest. The excess concentration of NE-OBD was obtained as an increase in the concentration of NE-OBD against the background level. On average, this value was 1.8- to 2.6-fold higher in the harvestable shoots than in the stubble for plants exposed to HDO vapour during the period when the harvestable shoots grew faster than the stubble. Our results suggest that the separation of harvestable shoots and stubble, both of which are generally combined as one part in studies on the metabolism of organically bound tritium (OBT) in grass, could contribute to a realistic evaluation of OBT transfer from timothy to livestock.

Signal Filtering Enabled by Spike Voltage-Dependent Plasticity in Metalloporphyrin-Based Memristors.

Neural systems can selectively filter and memorize spatiotemporal information, thus enabling high-efficient information processing. Emulating such an exquisite biological process in electronic devices is of fundamental importance for developing neuromorphic architectures with efficient in situ edge/parallel computing, and probabilistic inference. Here a novel multifunctional memristor is proposed and demonstrated based on metalloporphyrin/oxide hybrid heterojunction, in which the metalloporphyrin layer allows for dual electronic/ionic transport. Benefiting from the coordination-assisted ionic diffusion, the device exhibits smooth, gradual conductive transitions. It is shown that the memristive characteristics of this hybrid system can be modulated by altering the metal center for desired metal-oxygen bonding energy and oxygen ions migration dynamics. The spike voltage-dependent plasticity stemming from the local/extended movement of oxygen ions under low/high voltage is identified, which permits potentiation and depression under unipolar different positive voltages. As a proof-of-concept demonstration, memristive arrays are further built to emulate the signal filtering function of the biological visual system. This work demonstrates the ionic intelligence feature of metalloporphyrin and paves the way for implementing efficient neural-signal analysis in neuromorphic hardware.

Ultrasmall Polymer Nanoparticles Formed by Instantaneous Nanosplitting of Surfactant-Free Emulsion.

Application of polymer nanoparticles has progressively broadened. There is now increasing interest in smaller polymer nanoparticles for use in organic solar cells and drug delivery systems. Unfortunately, it is difficult to control the particle size below 50 nm with conventional synthesis methods. Our previously proposed "two-step nanoprecipitation method" overcomes this problem. An oil-in-water emulsion is first formed from polymer solution and deionized water without using surfactant; it is then injected into ethanol to form particles. The particle formation mechanism in this method has now been investigated, and an interesting phenomenon was discovered: the injected droplets instantaneously split into nanosize droplets with a size of 100-150 nm. The splitting was very effective, and the formed nanosize droplets were virtually monodisperse. This occurred only for a mixture composition in which the surface tension of the poor solvent mixture (water and ethanol) equaled that of the good solvent. This composition also resulted in formation of the smallest particles. By adjusting the conditions, we were able to synthesize extremely small nanoparticles (∼5 nm) of poly(3-hexylthiophene). This method has the potential to synthesize nanoparticles composed of other types of materials, such as nonconductive polymers and small molecules.

Controllable Organic Resistive Switching Achieved by One-Step Integration of Cone-Shaped Contact.

Conductive filaments (CFs)-based resistive random access memory possesses the ability of scaling down to sub-nanoscale with high-density integration architecture, making it the most promising nanoelectronic technology for reclaiming Moore's law. Compared with the extensive study in inorganic switching medium, the scientific challenge now is to understand the growth kinetics of nanoscale CFs in organic polymers, aiming to achieve controllable switching characteristics toward flexible and reliable nonvolatile organic memory. Here, this paper systematically investigates the resistive switching (RS) behaviors based on a widely adopted vertical architecture of Al/organic/indium-tin-oxide (ITO), with poly(9-vinylcarbazole) as the case study. A nanoscale Al filament with a dynamic-gap zone (DGZ) is directly observed using in situ scanning transmission electron microscopy (STEM) , which demonstrates that the RS behaviors are related to the random formation of spliced filaments consisting of Al and oxygen vacancy dual conductive channels growing through carbazole groups. The randomicity of the filament formation can be depressed by introducing a cone-shaped contact via a one-step integration method. The conical electrode can effectively shorten the DGZ and enhance the localized electric field, thus reducing the switching voltage and improving the RS uniformity. This study provides a deeper insight of the multiple filamentary mechanisms for organic RS effect.

Heterologous expression of lcc1 from Lentinula edodes in tobacco BY-2 cells results in the production an active, secreted form of fungal laccase.

Laccase (Lcc) is a lignin-degrading enzyme produced by white-rot fungi and has been the subject of much interest in the field of bioremediation due to its ability to oxidize phenolic compounds. In this report, we describe the isolation and characterization of lcc1, a novel gene of Lentinula edodes that encodes Lcc1, and demonstrate that recombinant Lcc1 is expressed in an active, secreted form in tobacco BY-2 cells in culture. The open reading frame of lcc1 was 1,557 base pairs in length and encoded a putative protein of 518 amino acids. We introduced a chimeric form of lcc1 (CaMV35Sp:clcc1) into tobacco BY-2 cells and obtained several stable clcc1 transformants that expressed active Lcc1. Lcc1 activity in BY-2 culture media was higher than in cellular extracts, which indicated that recombinant Lcc1 was produced in a secreted form. Recombinant Lcc1 had a smaller apparent molecular weight and exhibited a different pattern of posttranslational modification than Lcc1 purified from L. edodes. The substrate specificity of purified recombinant Lcc1 was similar to L. edodes Lcc1, and both enzymes were able to decolorize the same set of dyes. These results suggest that heterologous expression of fungal Lcc1 in BY-2 cells will be a valuable tool for the production of sufficient quantities of active laccase for bioremediation.

Lentinula edodes tlg1 encodes a thaumatin-like protein that is involved in lentinan degradation and fruiting body senescence.

Lentinan is an antitumor product that is purified from fresh Lentinula edodes fruiting bodies. It is a cell wall component, comprising beta-1,3-glucan with beta-1,6-linked branches, which becomes degraded during postharvest preservation as a result of increased glucanase activity. In this study, we used N-terminal amino acid sequence to isolate tlg1, a gene encoding a thaumatin-like (TL) protein in L. edodes. The cDNA clone was approximately 1.0 kb whereas the genomic sequence was 2.1 kb, and comparison of the two indicated that tlg1 contains 12 introns. The tlg1 gene product (TLG1) was predicted to comprise 240 amino acids, with a molecular mass of 25 kD and isoelectric point value of 3.5. The putative amino acid sequence exhibits approximately 40% identity with plant TL proteins, and a fungal genome database search revealed that these TL proteins are conserved in many fungi including the basidiomycota and ascomycota. Transcription of tlg1 was not detected in vegetative mycelium or young and fresh mushrooms. However, transcription increased following harvest. Western-blot analysis demonstrated a rise in TLG1 levels following harvest and spore diffusion. TLG1 expressed in Escherichia coli and Aspergillus oryzae exhibited beta-1,3-glucanase activity and, when purified from the L. edodes fruiting body, demonstrated lentinan degrading activity. Thus, we suggest that TLG1 is involved in lentinan and cell wall degradation during senescence following harvest and spore diffusion.

Characterization of the Lentinula edodes exg2 gene encoding a lentinan-degrading exo-beta-1,3-glucanase.

Lentinan, an antitumor substance purified from Lentinula edodes, is degraded during post-harvest preservation as a result of increased glucanase activity. We isolated an exo-beta-1,3-glucanase encoding gene, exg2, from L. edodes which is a homologue of an exo-glucanase-encoding gene conserved in ascomycetous fungi. The exg2 gene was cloned as an approximately 2.4-kbp cDNA, and as a genomic sequence of 3.9-kbp. The product of the exg2 gene is predicted to contain 759 amino acids with a molecular weight of 79 kDa and a pI value of 4.6. The putative N-terminus of EXG2 is identical to the N-terminal sequences of lentinan-degrading enzymes, GNase I and II, and a custom-made anti-EXG2 peptide anti-serum cross-reacted with purified GNase I and II. Transcription and translation of exg2 was low in the gills of mature fruiting bodies, but increased after harvesting. We conclude that the exg2 gene is a lentinan-degrading enzyme-encoding-gene in L. edodes.

Important role of fungal intracellular laccase for melanin synthesis: purification and characterization of an intracellular laccase from Lentinula edodes fruit bodies.

A laccase (EC 1.10.3.2) was isolated from the fully browned gills of Lentinula edodes fruit bodies. The enzyme was purified to a homogeneous preparation using hydrophobic, cation-exchange and size-exclusion chromatography. SDS-PAGE analysis showed the purified laccase, Lcc 2, to be a monomeric protein of 58.0 kDa. The enzyme had an isoelectric point of around pH 6.9. The optimum pH for enzyme activity was around 3.0 against 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)diammonium salt (ABTS), and it was most active at 40 degrees C and stable up to 50 degrees C. The enzyme contained 8.6 % carbohydrate and some copper atoms. The enzyme oxidized ABTS, p-phenylenediamine, pyrogallol, guaiacol, 2,6-dimethoxyphenol, catechol and ferulic acid, but not veratryl alcohol and tyrosine. Beta-(3,4-dihydroxyphenyl)alanine (L-DOPA), which was not oxidized by a laccase previously reported from the culture filtrate of L. edodes, was also oxidized by Lcc 2, and the oxidative product of L-dopa was identified as L-DOPA quinone by HPLC analysis. Lcc 2 was able to oxidize phenolic compounds extracted from fresh gills to brown-coloured products, suggesting a role for laccase in melanin synthesis in this strain.