A barley gene cluster for the biosynthesis of diterpenoid phytoalexins

Phytoalexins are specialized metabolites that are induced upon pathogen infection and contribute to the defense arsenal of plants. Maize and rice produce multiple diterpenoid phytoalexins and there is evidence from genomic sequences that other monocots may also produce diterpenoid phytoalexins. Here we report on the identification and characterization of a gene cluster in barley (Hordeum vulgare cv. Golden Promise) that is involved in the production of a set of labdane-related diterpenoids upon infection of roots by the fungal pathogen Bipolaris sorikiniana. The cluster is localized on chromosome 2 , covers over 600 kb and comprises genes coding for a (+)-copalyl diphosphate synthase (HvCPS2), a kaurene synthase like (HvKSL4) and several cytochrome P450 oxygenases. Expression of HvCPS2 and HvKSL4 in yeast and Nicotiana benthamiana resulted in the production of a single major product, whose structure was determined to be of the cleistanthane type and was named hordediene. Co-expression of HvCPS2, HvKSL4 and one of the CYPs from the cluster (CYP89E31) afforded two additional products, hordetriene and 11-hydroxy-hordetriene. Both of these compounds could be detected in extracts of roots infected by B. sorikiniana, validating the function of these genes in planta. Furthermore, diterpenoids with multiple oxidations and with molecular masses of 316, 318 and 332 are induced in infected barley roots and secreted in the medium, indicating that additional oxidases, possibly from the same genomic cluster are involved in the production of these phytoalexins. Our results provide the basis for further investigation of the role of this gene cluster in the defense of barley against pathogens and more generally in the interaction with the microbiome.

Potentiality of Graphene Oxide and Polyoxometalate as Radionuclides Adsorbent to Restore the Environment after Fukushima Disaster: A Mini Review

This paper discusses the promising candidate of excellent materials, graphene oxide (GO) and polyoxometalates (POMs), for radionuclide adsorbent. In this perspective, the unique properties of GO and POMs make them ideal candidates for developing new composites having the ability to adsorb radionuclides, and several essential things are reviewed. First, the anchoring mechanism to deposit POM on the GO surface area by (i) carboxylation method, (ii) covalent bonding, and (iii) impregnation method. Second, the radionuclides removal mechanism is described in several systems: (i) coagulation, (ii) electrostatic interaction, (iii) ion trapping, and (iv) H+-exchange. Third, the experimental condition that employed to enlarge the sorption capacity such as (i) pH adjustment, (ii) employing multiple oxidations, and (iii) cation charge. A thorough understanding of the POM-anchored GO material can pave the way for future research on similar materials. It can also help in understanding the nature of the interactive collaboration present between GO and POM.

A Biosynthetic Numbering System for Diterpene Pyrones

Diterpene pyrones, spiroditerpenoids, and brevianes are names given to a series of fungal meroterpenoids that share common structural features and a common biosynthetic pathway elaborated by multiple oxidations, rearrangements, and cyclizations to produce the observed structural diversity. A unifying approach to the numbering of these fungal metabolites, based on a common biosynthetic progenitor, a geranylgeranyl-pyrone hybrid, is presented. This proposal will foster simplicity through a standardized numbering system that can be applied to the known members of this family, as well as to future metabolites.

Bis(tercarbazole) pyrene and tetrahydropyrene derivatives: photophysical and electrochemical properties, theoretical modeling, and OLEDs

The title compounds are compared to bis(carbazole) analogues. They exhibit multiple oxidations, dual fluorescence (in one case), and function as emissive layers in OLEDs.

Tuning of graphene oxide composition by multiple oxidations for carbon dioxide storage and capture of toxic metals

The chemical composition and properties of graphene oxide can be controlled by multiple oxidations.

Molecular structures, redox properties, and photosubstitution of ruthenium(II) carbonyl complexes of porphycene

Two ruthenium(II) carbonyl complexes of porphycene, (carbonyl)(pyridine)(2,7,12,17-tetra-n-propylporphycenato)ruthenium(II) (1) and (carbonyl)(pyridine)(2,3,6,7,12,13,16,17-octaethylpor-phycenato)ruthenium(II) (2), have been structurally characterized by single-crystal X-ray diffraction analysis. Cyclic voltammetry has revealed that the porphycene complexes undergo multiple oxidations and reductions in dichloromethane and the reduction potentials are highly positive compared to porphyrin analogs. UV-light irradiation (400 nm or shorter wavelength region) of a benzene solution of 1 and 2 containing external pyridine leads to dissociation of the carbonyl ligand from the ruthenium(II) centers to give the corresponding bis-pyridine complexes. The identical reaction has been also studied for a porphyrin derivative (carbonyl)(pyridine)(2,3,7,8,12,13,17,18-octaethylporphyriato)ruthenum(II) (3). The first-order kinetic analysis has revealed that the photosubstitution of all of the compounds occurs in the order of 10-3 s-1 at 298 K but proceeds faster for complexes of porphycene (1 and 2) than that of porphyrin (3).

Stable Isotopes and Radiocarbon

This chapter discusses the basic principles surrounding the application of stable isotopes in natural ecosystems, which are based on variations in the relative abundance of lighter isotopes from chemical rather than nuclear processes. Due to faster reaction kinetics of the lighter isotope of an element, reaction products in nature can be enriched in the lighter isotope. These fractionation processes can be complex, but have proven to be useful in determining geothermometry and paleoclimatology, as well as sources of organic matter in ecological studies. The most common stable isotopes used in oceanic and estuarine studies are 18O, 2H, 13C, 15N, and 34S. The preference for using such isotopes is related to their low atomic mass, significant mass differences in isotopes, covalent character in bonding, multiple oxidations states, and sufficient abundance of the rare isotope. Living plants and animals in the biosphere contain a constant level of 14C, but when they die there is no further exchange with the atmosphere and the activity of 14C decreases with a half-life of 5730 ± 40 yr; this provides the basis for establishing the age of archeological objects and fossil remains.

Reactions Catalyzed by Bacterial Cytochromes P450

The cytochromes P450 are a large family of oxidative haemoproteins that are responsible for a wide variety of oxidative transformations in a variety of organisms. This review focuses upon the reactions catalyzed specifically by bacterial enzymes, which includes aliphatic hydroxylation, alkene epoxidation, aromatic hydroxylation, oxidative phenolic coupling, heteroatom oxidation and dealkylation, and multiple oxidations including C–C bond cleavage. The potential for the practical application of the oxidizing power of these enzymes is briefly discussed.