Dual selective nitration in Arabidopsis: Almost exclusive nitration of PsbO and PsbP, and highly susceptible nitration of four non-PSII proteins, including peroxiredoxin II E.

Protein tyrosine nitration is a selective process, as revealed in studies of animals. However, evidence for selective protein nitration in plants is scarce. In this study, Arabidopsis plants were exposed to air with or without nitrogen dioxide at 40 ppm for 8 h in light.

Analysis of donors of electrons to photosystem I and cyclic electron flow by redox kinetics of P700 in chloroplasts of isolated bundle sheath strands of maize.

Bundle sheath chloroplasts of NADP-malic enzyme (NADP-ME) type C4 species have a high demand for ATP, while being deficient in linear electron flow and oxidation of water by photosystem II (PSII). To evaluate electron donors to photosystem I (PSI) and possible pathways of cyclic electron flow (CEF1) in isolated bundle sheath strands of maize (Zea mays L.), an NADP-ME species, light-induced redox kinetics of the reaction center chlorophyll of PSI (P700) were followed under aerobic conditions.

Singlet oxygen in plants--its significance and possible detection with double (fluorescent and spin) indicator reagents.

Direct detection of reactive oxygen species (ROS), especially singlet oxygen, in plants under stress conditions is of special importance, not only to identify primary events of oxidative damage, but also in studies exploring the potential role of ROS as signal molecules. Due to short life-times and diffusion distances of ROS, these tasks require highly reactive and selective indicator reagents, localized at the presumed site of production. In the present study, we compared four double sensors: ROS indicator reagents in which partial fluorescence quenching of a dansyl moiety occurs as a result of nitroxide radical formation from a sterically hindered amine constituent.

Protection against photooxidative injury of tobacco leaves by 2-alkenal reductase. Detoxication of lipid peroxide-derived reactive carbonyls.

Degradation of lipid peroxides leads to the formation of cytotoxic 2-alkenals and oxenes (collectively designated reactive carbonyls). The novel NADPH-dependent oxidoreductase 2-alkenal reductase (AER; EC 1.3.

Differential use of two cyclic electron flows around photosystem I for driving CO2-concentration mechanism in C4 photosynthesis.

Whereas linear electron flow (LEF) in photosynthesis produces both ATP and NADPH, the cyclic electron flow (CEF) around photosystem I has been shown to produce only ATP. Two alternative routes have been shown for CEF; NAD(P)H dehydrogenase (NDH)- and ferredoxin:plastoquinone oxidoreductase (FQR)-dependent flows, but their physiological relevance has not been elucidated in detail. Meanwhile, because C(4) photosynthesis requires more ATP than does C(3) photosynthesis to concentrate CO(2), it has not been clear how the extra ATP is produced.

Enhanced ferredoxin-dependent cyclic electron flow around photosystem I and alpha-tocopherol quinone accumulation in water-stressed ndhB-inactivated tobacco mutants.

Dissipation mechanisms of excess photon energy under water stress were studied in ndhB-inactivated tobacco (Nicotiana tabacum cv. Xanthi) mutants, which are impaired in NAD(P)H dehydrogenase-dependent cyclic electron flow around PSI. Relative leaf water content and net CO(2) assimilation decreased to 30% and almost zero, respectively, after 11-day water stress in the mutant and wild type plants.

Purification and cDNA cloning of chloroplastic monodehydroascorbate reductase from spinach.

The chloroplastic isoform of monodehydroascorbate (MDA) radical reductase was purified from spinach chloroplasts and leaves. The cDNA of chloroplastic MDA reductase was cloned, and its deduced amino acid sequence, consisting of 497 residues, showed high homology with those of putative organellar MDA reductases deduced from cDNAs of several plants. The amino acid sequence of the amino terminal of the purified enzyme suggested that the chloroplastic enzyme has a transit peptide consisting of 53 residues.

Characterization of photosynthetic electron transport in bundle sheath cells of maize. I. Ascorbate effectively stimulates cyclic electron flow around PSI.

Redox changes of the reaction-center chlorophyll of photosystem I (P700) and chlorophyll fluorescence yield were measured in bundle sheath strands (BSS) isolated from maize (Zea mays L.) leaves. Oxidation of P700 in BSS by actinic light was suppressed by nigericin, indicating the generation of a proton gradient across the thylakoid membranes of BSS chloroplasts.

Ascorbate in thylakoid lumen functions as an alternative electron donor to photosystem II and photosystem I.

The roles of ascorbate (Asc) in the thylakoid lumen to support photosynthetic electron transport are investigated. Asc can be photooxidized in photosystem (PS) II and PSI. When the water oxidase complex (WOC) was inactivated by acidic pH or by UV-B, Asc was photooxidized in PSII with Asc replacing water as the electron donor.

Crystallization and preliminary crystallographic analysis of monodehydroascorbate radical reductase from cucumber.

Monodehydroascorbate (MDA) radical reductase (EC 1.6.5.

THE WATER-WATER CYCLE IN CHLOROPLASTS: Scavenging of Active Oxygens and Dissipation of Excess Photons.

Photoreduction of dioxygen in photosystem I (PSI) of chloroplasts generates superoxide radicals as the primary product. In intact chloroplasts, the superoxide and the hydrogen peroxide produced via the disproportionation of superoxide are so rapidly scavenged at the site of their generation that the active oxygens do not inactivate the PSI complex, the stromal enzymes, or the scavenging system itself. The overall reaction for scavenging of active oxygens is the photoreduction of dioxygen to water via superoxide and hydrogen peroxide in PSI by the electrons derived from water in PSII, and the water-water cycle is proposed for these sequences.

The distribution and possible origin of blue-green fluorescence in control and stressed barley leaves.

Apart from red (chlorophyll a) fluorescence, ultraviolet (UV) excitation of plant leaves results in blue-green intrinsic light emission. In order to analyse the potentially modifying influence of stress on this blue-green fluorescence (BGF), and to determine its origin, the fluorescence was characterised by spectroscopy, and two and three dimensional microscopy in leaves of Hordeum vulgare L. under UV and drought stress.

The NADPH:quinone oxidoreductase P1-zeta-crystallin in Arabidopsis catalyzes the alpha,beta-hydrogenation of 2-alkenals: detoxication of the lipid peroxide-derived reactive aldehydes.

P1-zeta-crystallin (P1-ZCr) is an oxidative stress-induced NADPH:quinone oxidoreductase in Arabidopsis thaliana, but its physiological electron acceptors have not been identified. We found that recombinant P1-ZCr catalyzed the reduction of 2-alkenals of carbon chain C(3)-C(9) with NADPH. Among these 2-alkenals, the highest specificity was observed for 4-hydroxy-(2E)-nonenal (HNE), one of the major toxic products generated from lipid peroxides.

Detection of singlet oxygen and superoxide with fluorescent sensors in leaves under stress by photoinhibition or UV radiation.

In order to understand the physiological functions of reactive oxygen species (ROS) generated in leaves, their direct measurement in vivo is of special importance. Here we report experiments with two dansyl-based ROS sensors, the singlet oxygen specific DanePy and HO-1889NH, which is reactive to both singlet oxygen and superoxide radicals. Here we report in vivo detection of (1)O(2) and O(2)(-*) by fluorescence quenching of two dansyl-based ROS sensors, the (1)O(2) specific DanePy and HO-1889NH, which was reactive with both (1)O(2) and O(2)(-*).