Oxidative stress is an integral component of various stress conditions in plants, and this fact largely determines the substantial overlap in physiological and molecular responses to biotic and abiotic environmental challenges. In this review, we discuss the alterations in central metabolism occurring in plants experiencing oxidative stress. To focus on the changes in metabolite profile associated with oxidative stress per se, we primarily analyzed the information generated in the studies based on the exogenous application of agents, inducing oxidative stress, and the analysis of mutants displaying altered oxidative stress response. Despite of the significant variation in oxidative stress responses among different plant species and tissues, the dynamic and transient character of stress-induced changes in metabolites, and the strong dependence of metabolic responses on the intensity of stress, specific characteristic changes in sugars, sugar derivatives, tricarboxylic acid cycle metabolites, and amino acids, associated with adaptation to oxidative stress have been detected. The presented analysis of the available data demonstrates the oxidative stress-induced redistribution of metabolic fluxes targeted at the enhancement of plant stress tolerance through the prevention of ROS accumulation, maintenance of the biosynthesis of indispensable metabolites, and production of protective compounds. This analysis provides a theoretical basis for the selection/generation of plants with improved tolerance to oxidative stress and the development of metabolic markers applicable in research and routine agricultural practice.

The oxidation potentials of Mn II in aqueous solutions of bicarbonate, formate, acetate and oxalate are reported as a function of concentration and compared to the rate of photooxidation of these solutions by the Mn-depleted water-oxidizing complex of photosystem II (apo-WOC-PSII) from peas. Although all the carboxylate species lower considerably the oxidation potential of Mn II , only bicarbonate stimulates the electron transfer from Mn II to apo-WOC-PSII. On the basis of the electrochemical data it is proposed that the unique capability of Mn-bicarbonate complexes to be photooxidized by PSII could be due to four possible reasons: (i) significantly larger decrease in the oxidation potential of Mn II (down to 0.52 V); (ii) electroneutrality of the functional electron transfer complex; (iii) the more favorable energetics reflected in the two pK a values for H 2 CO 3 /HCO 3 À and HCO 3 À /CO 3 2À and greater number of proton transfer sites; and (iv) multiple composition possibilities for the Mn III photo-product as Mn III (HCO 3 À ) 3 , Mn III (HCO 3 À )(CO 3 2À) and Mn III (HCO 3 À ) 2 (OH À ) (due to the high Lewis acidity of Mn III (pK o 1).

Environmental stresses induce production of oxylipins synthesized by the two main biosynthetic branches, allene oxide synthase (AOS) and hydroperoxide lyase (HPL). Here, we investigate how waterlogging-mediated alteration of AOS-and HPL-derived metabolic profile results in modulation of central metabolism and ultimately enhanced tolerance to this environmental stress in Arabidopsis thaliana. Waterlogging leads to increased levels of AOS-and HPLderived metabolites, and studies of genotypes lacking either one or both branches further support the key function of these oxylipins in waterlogging tolerance. Targeted quantitative metabolic profiling revealed oxylipin-dependent alterations in selected primary metabolites, and glycolytic and citric acid cycle intermediates, as well as a prominent shift in sucrose cleavage, hexose activation, the methionine salvage pathway, shikimate pathway, antioxidant system, and energy metabolism in genotypes differing in the presence of one or both functional branches of the oxylipin biosynthesis pathway. Interestingly, despite some distinct metabolic alterations caused specifically by individual branches, overexpression of HPL partially or fully alleviates the majority of altered metabolic profiles observed in AOS-depleted lines. Collectively, these data identify the key role of AOS-and HPL-derived oxylipins in altering central metabolism, and further provide a metabolic platform targeted at identification of gene candidates for enhancing plant tolerance to waterlogging.

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Photosystem II (PSII)-enriched membranes retain the original PSII architecture in contrast to PSII cores or PSII supercomplexes, which are usually isolated from Chlamydomonas reinhardtii. Here, we present data that fully characterize the structural and functional properties of PSII complexes in isolated PSII-enriched membranes from C. reinhardtii. The preparations were isolated from wild-type (WT) and CAH3-deficient mutant cia3 as the influence of CAH3 on the PSII function was previously proposed. Based on the equal chlorophyll content, the PSII-enriched membranes from WT and cia3 have the same amount of reaction centers (RCs), cytochrome b559, subunits of the water-oxidizing complex, Mn ions, and carotenes. They differ in the ratio of other carotenoids, the parts of low/intermediate redox forms of cytochrome b559, and the composition of outer light-harvesting complexes. The preparations had 40% more chlorophyll molecules per RC compared to higher plants. Functionally, PSII-enriched membranes from WT and cia3 show the same photosynthetic activity at optimal pH 6.5. However, the preparations from cia3 contained more closed RCs even at pH 6.5 and showed more pronounced suppression of PSII photosynthetic activity at shift pH up to 7.0, established in the lumen of dark-adapted cells. Nevertheless, the PSII photosynthetic capacities remained the same.