Direct detection of free radicals and reactive oxygen species in thylakoids

UPLC-PDA-ESI/MS metabolic profiling of dill shoots bioactive fraction; evidence of its antioxidant and hepatoprotective effects in vitro and in vivo

Hydroxyl radical (^• OH) scavenging capacity of aqueous dill (Anethum graveolens L.) shoot (ADSh) extract was assessed using electron paramagnetic resonance (EPR) spectroscopy. ADSh extract (at concentrations of 0.5 and 10 mg/ml) exerted high (OH) radical scavenging power. ADSh extract was further fractionated on Diaion HP-20 column to yield five fractions. EPR spin-trapping assay revealed fraction 4 (eluted with 75% aq. MeOH) to possess (^• OH) radical scavenging capacity over a concentration range (0.01-10 mg/ml), whereas fraction 2 (eluted with 25% aq. MeOH) appeared to be pro-oxidant at concentration 0.01 mg/ml. UPLC-PDA-ESI-MS metabolite profiling of ADSh extract revealed 87 metabolites, of which 64 compounds were identified in fraction 4, the most active fraction. Furthermore, ADSh extract demonstrated a hepatoprotective effect against acetaminophen (APAP)-induced hepatotoxicity in rats. Pretreatment of rats with ADSh extract (200 mg/kg b.wt) markedly attenuated the increased in the serum hepatic enzyme levels. It also increased free glutathione level and total antioxidant capacity in the serum of treated rats. [Correction added on May 3, 2021, after first online publication: "rates" has been changed to "rats" in the previous sentence.] Additionally, levels of (TNF-α and IL-1β) were back to almost normal levels compared to the control group. The above findings suggest that ADSh extract has a protective effect against APAP-induced liver damage.

Senescence, Stress, and Reactive Oxygen Species

Generation of reactive oxygen species (ROS) is one of the earliest responses of plant cells to various biotic and abiotic stresses. ROS are capable of inducing cellular damage by oxidation of proteins, inactivation of enzymes, alterations in the gene expression, and decomposition of biomembranes. On the other hand, they also have a signaling role and changes in production of ROS can act as signals that change the transcription of genes that favor the acclimation of plants to abiotic stresses. Among the ROS, it is believed that H₂O₂ causes the largest changes in the levels of gene expression in plants. A wide range of plant responses has been found to be triggered by H₂O₂ such as acclimation to drought, photooxidative stress, and induction of senescence. Our knowledge on signaling roles of singlet oxygen (¹O₂) has been limited by its short lifetime, but recent experiments with a flu mutant demonstrated that singlet oxygen does not act primarily as a toxin but rather as a signal that activates several stress-response pathways. In this review we summarize the latest progress on the signaling roles of ROS during senescence and abiotic stresses and we give a short overview of the methods that can be used for their assessment.

TROL-FNR interaction reveals alternative pathways of electron partitioning in photosynthesis

In photosynthesis, final electron transfer from ferredoxin to NADP(+) is accomplished by the flavo enzyme ferredoxin:NADP(+) oxidoreductase (FNR). FNR is recruited to thylakoid membranes via integral membrane thylakoid rhodanase-like protein TROL. We address the fate of electrons downstream of photosystem I when TROL is absent. We have employed electron paramagnetic resonance (EPR) spectroscopy to study free radical formation and electron partitioning in TROL-depleted chloroplasts. DMPO was used to detect superoxide anion (O2(.-)) formation, while the generation of other free radicals was monitored by Tiron. Chloroplasts from trol plants pre-acclimated to different light conditions consistently exhibited diminished O2(.-) accumulation. Generation of other radical forms was elevated in trol chloroplasts in all tested conditions, except for the plants pre-acclimated to high-light. Remarkably, dark- and growth light-acclimated trol chloroplasts were resilient to O2(.-) generation induced by methyl-viologen. We propose that the dynamic binding and release of FNR from TROL can control the flow of photosynthetic electrons prior to activation of the pseudo-cyclic electron transfer pathway.

Reactive oxygen species: re-evaluation of generation, monitoring and role in stress-signaling in phototrophic organisms

This review provides an overview about recent developments and current knowledge about monitoring, generation and the functional role of reactive oxygen species (ROS) - H2O2, HO2, HO, OH(-), (1)O2 and O2(-) - in both oxidative degradation and signal transduction in photosynthetic organisms including microscopic techniques for ROS detection and controlled generation. Reaction schemes elucidating formation, decay and signaling of ROS in cyanobacteria as well as from chloroplasts to the nuclear genome in eukaryotes during exposure of oxygen-evolving photosynthetic organisms to oxidative stress are discussed that target the rapidly growing field of regulatory effects of ROS on nuclear gene expression.

Reactive oxygen intermediates produced by photosynthetic electron transport are enhanced in short-day grown plants

Leaves of tobacco plants grown in short days (8h light) generate more reactive oxygen species in the light than leaves of plants grown in long days (16h light). A two fold higher level of superoxide production was observed even in isolated thylakoids from short day plants. By using specific inhibitors of photosystem II and of the cytochrome b(6)f complex, the site of O(2) reduction could be assigned to photosystem I. The higher rate of O(2) reduction led to the formation of a higher proton gradient in thylakoids from short day plants. In the presence of an uncoupler, the differences in O(2) reduction between thylakoids from short day and long day plants were abolished. The pigment content and the protein content of the major protein complexes of the photosynthetic electron transport chain were unaffected by the growth condition. Addition of NADPH, but not of NADH, to coupled thylakoids from long day plants raised the level of superoxide production to the same level as observed in thylakoids from short day plants. The hypothesis is put forward that the binding of an unknown protein permits the higher rate of pseudocyclic electron flow in thylakoids from short-day grown plants and that this putative protein plays an important role in changing the proportions of linear, cyclic and pseudocyclic electron transport in favour of pseudocyclic electron transport. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.