Several reactive oxygen species (ROS) are continuously produced in plants as byproducts of aerobic metabolism. Depending on the nature of the ROS species, some are highly toxic and rapidly detoxified by various cellular enzymatic and nonenzymatic mechanisms. Whereas plants are surfeited with mechanisms to combat increased ROS levels during abiotic stress conditions, in other circumstances plants appear to purposefully generate ROS as signaling molecules to control various processes including pathogen defense, programmed cell death, and stomatal behavior. This review describes the mechanisms of ROS generation and removal in plants during development and under biotic and abiotic stress conditions. New insights into the complexity and roles that ROS play in plants have come from genetic analyses of ROS detoxifying and signaling mutants. Considering recent ROS-induced genome-wide expression analyses, the possible functions and mechanisms for ROS sensing and signaling in plants are compared with those in animals and yeast.

REACTIVE OXYGEN SPECIES: Metabolism, Oxidative Stress, and Signal Transduction

世界経済・社会統計 = World development indicators

Reactive oxygen species and antioxidant machinery in abiotic stress tolerance in crop plants

Increasing population and consumption are placing unprecedented demands on agriculture and natural resources. Today, approximately a billion people are chronically malnourished while our agricultural systems are concurrently degrading land, water, biodiversity and climate on a global scale. To meet the world's future food security and sustainability needs, food production must grow substantially while, at the same time, agriculture's environmental footprint must shrink dramatically. Here we analyse solutions to this dilemma, showing that tremendous progress could be made by halting agricultural expansion, closing 'yield gaps' on underperforming lands, increasing cropping efficiency, shifting diets and reducing waste. Together, these strategies could double food production while greatly reducing the environmental impacts of agriculture.

https://escholarship.org/content/qt6xw5g085/qt6xw5g085.pdf?t=ovfwpc

Solutions for a cultivated planet

Inhibition of anaerobic digestion process: A review

Factors affecting mass transfer limited biodegradation in saturated porous media.

l-Lactate-driven ferric and nitrate reduction was studied in Escherichia coli E4. Ferric iron reduction activity in E. coli E4 was found to be constitutive. Contrary to nitrate, ferric iron could not be used as electron acceptor for growth. “Ferric iron reductase” activity of 9 nmol Fe2+ mg-1 protein min-1 could not be inhibited by inhibitors for the respiratory chain, like Rotenone, quinacrine, Actinomycin A, or potassium cyanide. Active cells and l-lactate-driven nitrate respiration in E. coli E4 leading to the production of nitrite, was reduced to about 20% of its maximum activity with 5 mM ferric iron, or to about 50% in presence of 5 mM ferrous iron. The inhibition was caused by nitric oxide formed by a purely chemical reduction of nitrite by ferrous iron. Nitric oxide was further chemically reduced by ferrous iron to nitrous oxide. With electron paramagnetic resonance spectroscopy, the presence of a free [Fe2+-NO] complex was shown. In presence of ferrous or ferric iron and l-lactate, nitrate was anaerobically converted to nitric oxide and nitrous oxide by the combined action of E. coli E4 and chemical reduction reactions (chemodenitrification).

Ferrous iron dependent nitric oxide production in nitrate reducing cultures of Escherichia coli

The transport of P(i) was characterized in Acinetobacter johnsonii 210A, which is able to accumulate an excessive amount of phosphate as polyphosphate (polyP) under aerobic conditions. P(i) is taken up against a concentration gradient by energy-dependent, carrier-mediated processes. A. johnsonii 210A, grown under P(i) limitation, contains two uptake systems with Kt values of 0.7 +/- 0.2 microM and 9 +/- 1 microM. P(i) uptake via the high-affinity component is drastically reduced by N,N'-dicyclohexylcarbodiimide, an inhibitor of H(+)-ATPase, and by osmotic shock. Together with the presence of P(i)-binding activity in concentrated periplasmic protein fractions, these results suggest that the high-affinity transport system belongs to the group of ATP-driven, binding-protein-dependent transport systems. Induction of this transport system upon transfer of cells grown in the presence of excess P(i) to P(i)-free medium results in a 6- to 10-fold stimulation of the P(i) uptake rate. The constitutive low-affinity uptake system for P(i) is inhibited by uncouplers and can mediate counterflow of P(i), indicating its reversible, secondary nature. The presence of an inducible high-affinity uptake system for P(i) and the ability to decrease the free internal P(i) pool by forming polyP enable A. johnsonii 210A to reduce the P(i) concentration in the aerobic environment to micromolar levels. Under anaerobic conditions, polyP is degraded again and P(i) is released via the low-affinity secondary transport system.

Characterization of two phosphate transport systems in Acinetobacter johnsonii 210A.

In this study, we characterized four Tn5 mutants derived from Rhizobium leguminosarum RBL5515 with respect to synthesis and secretion of cellulose fibrils, extracellular polysaccharides (EPS), capsular polysaccharides, and cyclic beta-(1,2)-glucans. One mutant, strain RBL5515 exo-344::Tn5, synthesizes residual amounts of EPS, the repeating unit of which lacks the terminal galactose molecule and the substituents attached to it. On basis of the polysaccharide production pattern of strain RBL5515 exo-344::Tn5, the structural features of the polysaccharides synthesized, and the results of an analysis of the enzyme activities involved, we hypothesize that this strain is affected in a galactose transferase involved in the synthesis of EPS only. All four mutants failed to nodulate plants belonging to the pea cross-inoculation group; on Vicia sativa they induced root hair deformation and rare abortive infection threads. All of the mutants appeared to be pleiotropic, since in addition to defects in the synthesis of EPS, lipopolysaccharide, and/or capsular polysaccharides significant increases in the synthesis and secretion of cyclic beta-(1,2)-glucans were observed. We concluded that it is impossible to correlate a defect in the synthesis of a particular polysaccharide with nodulation characteristics.

Polysaccharide synthesis in relation to nodulation behavior of Rhizobium leguminosarum

Enzyme measurements were carried out with crude cell-free extracts of the propionate oxidizing coculture of Syntrophobacter wolinii and Desulfovibrio G11. Using cell-free extracts of a pure culture of Desulfovibrio G11 as a blank, most of the enzymes involved in the methylmalonyl-CoA pathway for propionate oxidation, including a propionyl-CoA: oxaloacetate transcarboxylase, were demonstrated in S. wolinii.

Alexander J. B. Zehnder

Papers

Factors affecting mass transfer limited biodegradation in saturated porous media.

Ferrous iron dependent nitric oxide production in nitrate reducing cultures of Escherichia coli

Characterization of two phosphate transport systems in Acinetobacter johnsonii 210A.

Polysaccharide synthesis in relation to nodulation behavior of Rhizobium leguminosarum

Enzymatic evidence for involvement of the methylmalonyl-CoA pathway in propionate oxidation by Syntrophobacter wolinii.