Evidence for two Qa-like quinone binding sites in the reaction centre of Rhodopseudomonas viridis

The oxidation-reduction potential of the iron-quinone electron acceptors in the reaction centre of Rhodopseudomonas viridis has been reinvestigated. In chromatophores treated with o-phenanthroline to remove the secondary acceptor Q_b, two steps were observed in the reduction of the primary electron acceptor Q_a with E_m ≈ − 100 and ≈ − 330 mV. In isolated reaction centres only one step was observed in the reduction of Q_a with E ≈ −150 mV. Reconstitution of the reaction centres with additional menaquinone resulted in an increase in the Q_a EPR signal and reconstitution of the low-potential step in the oxidation-reduction titration. Reconstitution with ubiquinone resulted in the recovery of the secondary quinone Q_b. The addition of ubiquinone did not reconstitute the low-potential step of Q_a reduction, or affect the reconstitution of this step by menaquinone. It is concluded that menaquinone can bind to two sites on the reaction centre. Both have properties of the Q_a site but with different pK values. It is unlikely that either is the same as the Q_b site.     

A Class of Phase-Confounded Designs

A new class of phase-confounded designs is suggested. The class possesses the property that if in a year one of the rotations carries the test crop all other rotations also do. It also leads to equal block sizes when the rotations are structured in specified ways. Conditions under which designs of this class exist as well as method of constructing them are discussed.     

Soil Organic Matter and Management of Plant-Parasitic Nematodes

Organic matter and its replenishment has become a major component of soil health management programs. Many of the soil''s physical, chemical, and biological properties are a function of organic matter content and quality. Adding organic matter to soil influences diverse and important biological activities. The diversity and number of free-living and plant-parasitic nematodes are altered by rotational crops, cover crops, green manures, and other sources of organic matter. Soil management programs should include the use of the proper organic materials to improve soil chemical, physical, and biological parameters and to suppress plant-parasitic nematodes and soilborne pathogens. It is critical to monitor the effects of organic matter additions on activities of major and minor plant-parasitic nematodes in the production system. This paper presents a general review of information in the literature on the effects of crop rotation, cover crops, and green manures on nematodes and their damage to economic crops.     

Towards a unified mechanism of biological methane oxidation

Abstract The biological oxidation of methane to methanol is catalysed by soluble and particulate forms of the enzyme methane monooxygenase. Little information is available regarding the structure and mechanism of the particulate enzyme whereas much is known about the soluble form of the enzyme. This review concentrates on current knowledge of the structure of the components of the soluble methane monooxygenase and draws together these results with those on the kinetics and substrate specificity of the enzyme in a possible chemical mechanism for enzymatic methane oxidation.     

Dicarboxyamylose and dicarboxycellulose,stereoregular polyelectrolytes: physicochemical characterization and interaction with divalent cations

2,3-Dicarboxyamylose (DCA) and 2,3-dicarboxycellulose (DCC) have been obtained by splitting with periodate of all the C(2)C(3) bonds of amylose and cellulose, and further oxidation (with chlorite) of the corresponding polydialdehydes. Small, but reproducible, differences of ¹³C chemical shifts in dicate that DCA and DCC retained the different configuration at C-1 of the original polysaccharides, therefore being stereoisomers. The potentiometric and conductimetric titration curves of DCA and DCC and the pH-dependence of their ¹H n.m.r. spectra are those of typical polydicarboxylates. Interaction of DCA and DCC (Na salts) with divalent cations is clearly indicated by inflexions in conductimetric titration curves with Ca²⁺, Mg²⁺, Cu²⁺ and Fe²⁺, and by variation in specific optical rotation.     

Hydrogen fertilization of soils – is this a benefit of legumes in rotation?

Hydrogen gas (H₂) is an obligate byproduct of the N₂‐fixing enzyme, nitrogenase, claiming about 5–6% of the crops’ net photosynthesis but most, if not all of the H₂ lost from nodules is oxidized by the soil surrounding the root system of the plant. When soils not recently used to support the growth of legumes were exposed to H₂ gas at a rate and duration similar to that of soil adjacent to legume nodules, the fertility of the soil was enhanced in comparison with soil treated with air. Under growth‐chamber and field conditions, H₂‐treated soils improved the growth performance of spring wheat, canola, barley and soybean (non‐symbiotic) when compared with untreated soils or with soils pretreated with air. The dry weights of 4‐ to 7‐week‐old plants were 15–48% greater in the H₂‐treated soil, and in barley and spring wheat, tiller number of 7‐week‐old plants were 36 and 48% greater in the H₂‐treated soils. These findings may contribute to an explanation for the persistence of H₂ evolving associations in agricultural legume symbioses selected for high yields (Uratsu et al., Crop Science 22, 600–602, 1982) and suggest that it may be possible to isolate, identify and culture the micro‐organisms that are responsible for at least some of the benefits of legumes in crop rotation.     

The chirality of the mitotic spindle provides a mechanical response to forces and depends on microtubule motors and augmin

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Plant and Soil Nematodes: Societal Impact and Focus for the Future.

Plant and soil nematodes significandy impact our lives. Therefore, we must understand and manage these complex organisms so that we may continue to develop and sustain our food production systems, our natural resources, our environment, and our quality of life. This publication looks specifically at soil and plant nematology. First, the societal impact of nematodes and benefits of nematology research are briefly presented. Next, the opportunities facing nematology in the next decade are outlined, as well as the resources needed to address these priorities. The safety and sustainability of U.S. food and fiber production depends on public and administrative understanding of the importance of nematodes, the drastic effects of nematodes on many agricultural and horticultural crops, and the current research priorities of nematology.