Photooxidative Stress Research Articles

Disruption of a Upf1-like helicase-encoding gene OsPLS2 triggers light-dependent premature leaf senescence in rice.

The OsPLS2 locus was isolated and cloned by map-based cloning that encodes a Upf1-like helicase. Disruption of OsPLS2 accelerated light-dependent leaf senescence in the rice mutant of ospls2. Leaf senescence is a very complex physiological process controlled by both genetic and environmental factors, however its underlying molecular mechanisms remain elusive. In this study, we report a novel Oryza sativa premature leaf senescence mutant (ospls2). Through map-based cloning, a G-to-A substitution was determined at the 1st nucleotide of the 13th intron in the OsPLS2 gene that encodes a Upf1-like helicase. This mutation prompts aberrant splicing of OsPLS2 messenger and consequent disruption of its full-length protein translation, suggesting a negative role of OsPLS2 in regulating leaf senescence. Wild-type rice accordingly displayed a progressive drop of OsPSL2 protein levels with age-dependent leaf senescence. Shading and light filtration studies showed that the ospls2 phenotype, which was characteristic of photo-oxidative stress and reactive oxygen species (ROS) accumulation, was an effect of irritation by light. When continuously exposed to far-red light, exogenous H2O2 and/or abscisic acid (ABA), the ospls2 mutant sustained hypersensitive leaf senescence. In consistence, light and ROS signal pathways in ospls2 were activated by down-regulation of phytochrome genes, and up-regulation of PHYTOCHROME-INTERACTING FACTORS (PIFs) and WRKY genes, all promoting leaf senescence. Together, these data indicated that OsPLS2 played an essential role in leaf senescence and its disruption triggered light-dependent leaf senescence in rice.

Phylogenetic signature of light and thermal stress for the endosymbiotic dinoflagellates of corals (Family Symbiodiniaceae)

AbstractCoral reefs around the world have been affected by a climate‐change induced phenomenon known as “coral bleaching,” which is caused by the interaction between high irradiance and elevated seawater temperatures, and involves the mass expulsion of Symbiodiniaceae from anemones, sponges, and corals. The primary drivers of this phenomenon are the inherent genetic variability in the Family Symbiodiniaceae, and the variability in the abiotic environment for variables such as irradiance and temperature. Recent experiments have either disregarded the important interactive role of irradiance or have suggested that photooxidative stress is not a prerequisite for coral bleaching because certain reactive oxygen species (ROS) can be produced in the dark. Here, fluorescent probes are used as proxies for the relative concentration of ROS in different genera of cultured Symbiodiniaceae under varying thermal and light conditions. The results show that taxon‐specific patterns of the concentration of ROS are observed but that all genera tested produced significantly greater amounts of superoxide radicals and hydrogen peroxide, compared to singlet oxygen, when exposed to high light and thermal stress. These results are contextualized in relation to the primary drivers of ROS production and the photo‐physiological basis for differences in ROS production that may then be correlated with symbiont driven coral bleaching.

Redox Systemic Signaling and Induced Tolerance Responses During Soybean-Bradyrhizobium japonicum Interaction: Involvement of Nod Factor Receptor and Autoregulation of Nodulation.

The symbiotic relationship between legumes and nitrogen-fixing rhizobia induces local and systemic responses, which ultimately lead to nodule formation. The autoregulation of nodulation (AON) is a systemic mechanism related to innate immunity that controls nodule development and involves different components ranging from hormones, peptides, receptors to small RNAs. Here, we characterized a rapid systemic redox changes induced during soybean–Bradyrhizobium japonicum symbiotic interaction. A transient peak of reactive oxygen species (ROS) generation was found in soybean leaves after 30 min of root inoculation with B. japonicum. The ROS response was accompanied by changes in the redox state of glutathione and by activation of antioxidant enzymes. Moreover, the ROS peak and antioxidant enzyme activation were abolished in leaves by the addition, in either root or leaf, of DPI, an NADPH oxidase inhibitor. Likewise, these systemic redox changes primed the plant increasing its tolerance to photooxidative stress. With the use of non-nodulating nfr5-mutant and hyper-nodulating nark-mutant soybean plants, we subsequently studied the systemic redox changes. The nfr5-mutant lacked the systemic redox changes after inoculation, whereas the nark-mutant showed a similar redox systemic signaling than the wild type plants. However, neither nfr5- nor nark-mutant exhibited tolerance to photooxidative stress condition. Altogether, these results demonstrated that (i) the early redox systemic signaling during symbiotic interaction depends on a Nod factor receptor, and that (ii) the induced tolerance response depends on the AON mechanisms.

Differences between Motile and Nonmotile Cells of Haematococcus pluvialis in the Production of Astaxanthin at Different Light Intensities.

Haematococcus pluvialis, as the best natural resource of astaxanthin, is widely used in nutraceuticals, aquaculture, and cosmetic industries. The purpose of this work was to compare the differences in astaxanthin accumulation between motile and nonmotile cells of H. pluvialis and to determine the relationship between the two cells and astaxanthin production. The experiment design was achieved by two different types of H. pluvialis cell and three different light intensities for an eight day induction period. The astaxanthin concentrations in nonmotile cell cultures were significantly increased compared to motile cell cultures. The increase of astaxanthin was closely associated with the enlargement of cell size, and the nonmotile cells were more conducive to the formation of large astaxanthin-rich cysts than motile cells. The cyst enlargement and astaxanthin accumulation of H. pluvialis were both affected by light intensity, and a general trend was that the higher the light intensity, the larger the cysts formed, and the larger the quantity of astaxanthin accumulated. In addition, the relatively low cell mortality rate in the nonmotile cell cultures indicated that the nonmotile cells have a stronger tolerance to photooxidative stress. We suggest that applying nonmotile cells as the major cell type of H. pluvialis to the induction period may help to enhance the content of astaxanthin and the stability of astaxanthin production.

Photochemical Efficiencies in Reef-Dwelling Anthozoans: Insights from “Survivor” Species

In recent decades, populations of many coral species have declined dramatically on reefs worldwide. A major factor in coral mortality has been photo-oxidative stress associated with both solar irradiance and elevated temperatures. While many studies have focused on species that have declined, fewer efforts have focused on the “survivor” species, those that have maintained relatively stable populations or even increased in abundance. The objective of this study was to assess temporal variability in photochemical efficiencies (Fv/Fm) as an indicator of potential photo-oxidative stress in the dinoflagellate symbionts in three species, the scleractinians Siderastrea siderea and Montastraea cavernosa, and the zoanthid Palythoa caribaeorum, whose populations have remained relatively stable along the Florida reef tract. Coral colonies with no visual indication of disease or bleaching were assessed quarterly in 2012 and 2013, at sites at 6 or 18 m depths. Colonies were dark-acclimated prior to measurements using pulse-amplitude modulated fluorometry. The mean Fv/Fm values for P. caribaeorum colonies assessed at 6 m depth were consistently the lowest (0.59, 0.02 SE). Siderastrea siderea assessed at both 6 and 18 m revealed significantly lower Fv/Fm values (p=0.0006) for those living at 6 m (0.64, 0.02 SE) than for those living at 18 m (0.68, 0.01 SE) depths. The Fv/Fm values for colonies of M. cavernosa assessed at 18 m also averaged 0.68 (0.01 SE). Thus, photochemical efficiencies were lower in colonies living at 6 m than in colonies living at 18 m, while no significant seasonal differences were found in the mean Fv/Fm values in the examined species. This study provides the first known report of photochemical efficiency in P. caribaeorum.

An LC-MS profiling method reveals a route for apocarotene glycosylation and shows its induction by high light stress in Arabidopsis.

Apocarotenoid glycosylation serves as a valve regulating carotenoid homeostasis in plants and may contribute to their response to photo-oxidative stress. However, an analytical method that allows comprehensive and sensitive profiling of glycosylated apocarotenoids (GAPOs) is still missing. We developed an efficient ultra-high performance liquid chromatography-high resolution-mass spectrometry (UHPLC-HR-MS) method to analyze 25 GAPOs present in carotenoid-accumulating E. coli cells and plant tissues. Optimized HR-heated-electrospray ionization (HESI)-MS parameters enabled, based on HR MS and tandem mass spectrometry (MS/MS) data, the identification of yet undescribed GAPOs from Arabidopsis, which include Glc-apo-11-carotenal (GAPO11), Glc-apo-13-carotenone (GAPO13), and their isomers. The identity of these compounds was confirmed by the transformation of deuterium-labelled non-hydroxylated carotene cleavage products into the corresponding GAPOs in planta. Quantitative analysis of GAPOs in Arabidopsis showed that the levels of Glc-cyclocitral (GAPO7), Glc-cyclocitral isomer I (GAPO7I), Glc-ionone (GAPO9), Glc-ionone isomer I (GAPO9I), Glc-apo-11-carotenal isomer I (GAPO11I), Glc-apo-13-carotenone (GAPO13), and Glc-apo-13-carotenone isomers (GAPO13I, GAPO13II, and GAPO13III) significantly increase after high light (HL) treatment. This treatment also led to an obvious increase in the levels of most carotene- and all xanthophyll-derived apocarotenoids detected in our system. Our work demonstrates for the first time that HL stress induces apocarotenoid glycosylation in Arabidopsis and unravels a novel plant metabolic pathway that leads from carotene cleavage products to GAPOs that are identical to xanthophyll derived GAPOs. Thus, our new approach allows sensitive and reliable profiling of GAPOs, which is crucial for understanding the function of apocarotenoid glycosylation in plants and its role in the acclimation to HL stress.

MicroRNA-29 enhances autophagy and cleanses exogenous mutant αB-crystallin in retinal pigment epithelial cells

Retinal pigment epithelial cells (RPEs), a pigmented cell layer in the outer retina, are constantly exposed to photo-oxidative stress. Autophagy relieves the stress by removing oxidative protein adducts, protein aggregates, and damaged mitochondria. We previously found that miR-29 is downregulated in choroid/RPE tissue in a model of exudative age-related macular degeneration (AMD), suggesting that miR-29 deficiency may contribute to autophagy inhibition and AMD progression. Here we wanted to test whether overexpression of miR-29 in RPEs could enhance autophagy, thereby facilitating removal of drusen components. Indeed, overexpression of miR-29 in the RPEs increased autophagy, assessed by decreased protein levels of p62, increased lipid form of microtubule-associated protein light chain (LC3-II), and elevated autophagy flux. Furthermore, overexpression of miR-29 mitigated the formation of mutant αB-crystallin (R120G) protein aggregates. In probing the mechanism, we demonstrated that miR-29 post-transcriptionally repressed LAMPTOR1/p18 via targeting its 3’-UTRs of messenger RNA. MiR-29 overexpression and knockdown of LAMPTOR1/p18 led to limited mTORC1 recruitment to lysosomes and inhibition of mTORC1 activity. Altogether, miR-29 enhances autophagy which aids in removal of protein aggregates. These findings reveal a novel role of miR-29, which has the potential of being a therapeutic strategy for rescuing RPE degeneration in ocular disorders.

Protein phosphatases meet reactive oxygen species in plant signaling networks

The cellular redox state is vital for the survival of all living systems. The dynamic nature of reactive oxygen species (ROS) are reflected in their functioning both as a damage causal and control agent. They are known primarily for causing oxidative damage and induction of programmed cell death (PCD) in case of pathogen attacks to prevent pathogen proliferation, while at low levels, they act as signal transducer(s) in different signaling pathways. Protein phosphatase(s) and kinase(s) co-ordinate the reversible post-translational modification of proteins, thereby, regulating a number of signaling pathways. In plant systems, protein kinases outnumber the protein phosphatases, which is countered by the diverse functional assemblage of the latter. Protein phosphatases are redox-regulated through reversible oxidation of critical Cysteine (Cys) residues leading to their activation and inactivation. Thus, their diversity and critical involvement in a number of cellular processes, which require redox homeostasis as a crucial element, brings them under the control of redox regulation. The observations made with regard to their involvement in photo-oxidative stress and responses involving ROS as signaling molecules, make a strong case for the potential of protein phosphatases in ROS signaling, with an emphasis on stress biology. In this review, we present the common ground on which ROS and protein phosphatases operate in view of their regulatory functions.

Physiological and Biochemical Responses of Cucumis melo L. Chloroplasts to Low-Phosphate Stress.

Phosphorus (P) is a limiting plant soil nutrient. Long-term low inorganic phosphate (Pi) irreversibly damages plant cells and hinders plant growth. Plants have evolved several adaptive biochemical, physiological, and developmental responses to low-Pi stress. However, little is known about chloroplast responses to low-Pi stress. In this study, we used physiological and biochemical analyses to investigate melon chloroplast responses to low-Pi stress. The results indicated that low-Pi stress impeded melon seedling growth and reduced its dry matter content by inhibiting the photosynthesis. Low-Pi stress reduced the P content in shoots, which inhibited ATP synthase (ATP-ase) activity, and disturbed the proton and electron transport efficiency on chloroplast photosynthetic electron transport chain. In addition, low-Pi stress induced reactive oxygen species (ROS) production in the leaves, which caused membrane peroxidation. Therefore, redox homeostasis was not maintained, and the melon leaves presented with symptoms of photooxidative stress. To mitigate photoinhibition, the melon plants initiated non-photochemical chlorophyll fluorescence quenching (NPQ) initiated by acidification of the thylakoid lumen to dissipate excess excitation energy, significantly improved ROS-scavenging enzyme activity. Based on these experimental results, we concluded that low Pi inhibited photosystem activity and caused photooxidative stress and photoinhibition. To alleviate these negative effects, the plant activated its NPQ mechanism, alternative electron transport pathways, and antioxidant system to protect its chloroplasts.

Organic radical imaging in plants: Focus on protein radicals

Biomolecule (lipid and protein) oxidation products formed in plant cells exposed to photooxidative stress play a crucial role in the retrograde signaling and oxidative damage. The oxidation of biomolecules initiated by reactive oxygen species is associated with formation of organic (alkyl, peroxyl and alkoxyl) radicals. Currently, there is no selective and sensitive technique available for the detection of organic radicals in plant cells. Here, based on the analogy with animal cells, immuno-spin trapping using spin trap, 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was used to image organic radicals in Arabidopsis leaves exposed to high light. Using antibody raised against the DMPO nitrone adduct conjugated with the fluorescein isothiocyanate, organic radicals were imaged by confocal laser scanning microscopy. Organic radicals are formed predominantly in the chloroplasts located at the periphery of the cells and distributed uniformly throughout the grana stack. Characterization of protein radicals by standard immunological techniques using anti-DMPO antibody shows protein bands with apparent molecular weights of 32 and 34 kDa assigned to D1 and D2 proteins and two protein bands below the D1/D2 band with apparent molecular weights of 23 and 18 kDa and four protein bands above the D1/D2 band with apparent molecular weights of 41, 43, 55 and 68 kDa. In summary, imaging of organic radicals by immuno-spin trapping represents selective and sensitive technique for the detection of organic radicals that might help to clarify mechanistic aspects on the role of organic radicals in the retrograde signaling and oxidative damage in plant cell.

Topical nanodelivery system of lutein for the prevention of selenite-induced cataract

Cataracts are responsible for half of the world blindness, surgery being the only viable treatment. Lutein, a naturally occurring carotenoid in the eye, has the potential to reduce cataract progression by protecting the eye from photo-oxidative stress. To restore the eye's natural line of defense against photo-oxidative stress, a formulation was developed using zein and poly(lactic-co-glycolic acid) nanoparticles (NPs) embedded in an optimized bioadhesive thermosensitive gel for the delivery of lutein via topical application. Cataracts were induced in Crl:WI rats via selenite injection at 13 days post-partum, followed by 7 days of treatment with free lutein or lutein-loaded NPs administered orally or topically. Cataract severity was significantly reduced in rats treated with topical applications of lutein-loaded NPs compared to the positive control, while no significant differences were observed in rats treated with other lutein formulations including oral and topically applied free lutein.

Decoding β-Cyclocitral-Mediated Retrograde Signaling Reveals the Role of a Detoxification Response in Plant Tolerance to Photooxidative Stress.

When exposed to unfavorable environmental conditions, plants can absorb light energy in excess of their photosynthetic capacities, with the surplus energy leading to the production of reactive oxygen species and photooxidative stress. Subsequent lipid peroxidation generates toxic reactive carbonyl species whose accumulation culminates in cell death. β-Cyclocitral, an oxidized by-product of β-carotene generated in the chloroplasts, mediates a protective retrograde response that lowers the levels of toxic peroxides and carbonyls, limiting damage to intracellular components. In this study, we elucidate the molecular mechanism induced by β-cyclocitral in Arabidopsis thaliana and show that the xenobiotic detoxification response is involved in the tolerance to excess light energy. The involvement of the xenobiotic response suggests a possible origin for this pathway. Furthermore, we establish the hierarchical structure of this pathway that is mediated by the β-cyclocitral-inducible GRAS protein SCARECROW LIKE14 (SCL14) and involves ANAC102 as a pivotal component upstream of other ANAC transcription factors and of many enzymes of the xenobiotic detoxification response. Finally, the SCL14-dependent protective mechanism is also involved in the low sensitivity of young leaf tissues to high-light stress.

NDRG2 suppression as a molecular hallmark of photoreceptor-specific cell death in the mouse retina

Photoreceptor cell death is recognized as the key pathogenesis of retinal degeneration, but the molecular basis underlying photoreceptor-specific cell loss in retinal damaging conditions is virtually unknown. The N-myc downstream regulated gene (NDRG) family has recently been reported to regulate cell viability, in particular NDRG1 has been uncovered expression in photoreceptor cells. Accordingly, we herein examined the potential roles of NDRGs in mediating photoreceptor-specific cell loss in retinal damages. By using mouse models of retinal degeneration and the 661 W photoreceptor cell line, we showed that photoreceptor cells are indeed highly sensitive to light exposure and the related oxidative stress, and that photoreceptor cells are even selectively diminished by phototoxins of the alkylating agent N-Methyl-N-nitrosourea (MNU). Unexpectedly, we discovered that of all the NDRG family members, NDRG2, but not the originally hypothesized NDRG1 or other NDRG subtypes, was selectively expressed and specifically responded to retinal damaging conditions in photoreceptor cells. Furthermore, functional experiments proved that NDRG2 was essential for photoreceptor cell viability, which could be attributed to NDRG2 control of the photo-oxidative stress, and that it was the suppression of NDRG2 which led to photoreceptor cell loss in damaging conditions. More importantly, NDRG2 preservation contributed to photoreceptor-specific cell maintenance and retinal protection both in vitro and in vivo. Our findings revealed a previously unrecognized role of NDRG2 in mediating photoreceptor cell homeostasis and established for the first time the molecular hallmark of photoreceptor-specific cell death as NDRG2 suppression, shedding light on improved understanding and therapy of retinal degeneration.

Oxidative stress induced in chloroplasts or mitochondria promotes proline accumulation in leaves of pea (Pisum sativum): another example of chloroplast-mitochondria interactions.

Oxidative stress can occur in different parts of plant cells. We employed two oxidants that induce reactive oxygen species (ROS) in different intracellular compartments: methyl viologen (MV, in chloroplasts) and menadione (MD, in mitochondria). The responses of pea (Pisum sativum) leaf discs to MV or MD after 4-h incubation in dark or moderate (300μEm-2s-1) or high light (1200μEm-2s-1) were examined. Marked increase in ROS levels was observed, irrespective of compartment targeted. The levels of proline, a compatible solute, increased markedly much more than that of ascorbate or glutathione during oxidative/photo-oxidative stress, emphasizing the importance of proline. Further, the activities and transcripts of enzymes involved in biosynthesis or oxidation of proline were studied. An upregulation of biosynthesis and downregulation of oxidation was the basis of proline accumulation. Pyrroline-5-carboxylate synthetase (P5CS, involved in biosynthesis) and proline dehydrogenase (PDH, involved in oxidation) were the key enzymes regulated under oxidative stress. Since these two enzymes-P5CS and PDH-are located in chloroplasts and mitochondria, respectively, we suggest that proline metabolism can help to mediate inter-organelle interactions and achieve redox homeostasis under photo-oxidative stress.

Chlororespiration induces non-photochemical quenching of chlorophyll fluorescence during darkness in lichen chlorobionts.

Lichens and their algal partners are desiccation‐tolerant organisms and as such survive after the complete loss of water. This trait is the consequence of several physiological, biochemical and structural features, including specific mechanisms dissipating excess light to avoid photooxidative stress. The maximum quantum yield of photosystem II (PSII; Fv/Fm) is widely used as a sensitive indicator of photosynthetic performance and is calculated after complete relaxation in darkness of the fluorescence quenching associated with active light energy dissipation mechanisms. Unexpectedly, we observed that lichens and isolated chlorobionts (chlorophyte symbionts in lichen) maintained in darkness for several hours showed a strong decrease in the ratio Fv/Fm, which was reversible after re‐illumination. We analyzed this dark‐induced Fv/Fm decay in the chlorobiont Asterochloris erici through steady‐state and fast‐induction kinetics of chlorophyll a fluorescence and simultaneous P700 oxidation measurements. We found that the gradual decay of Fv/Fm in darkness was caused by reversible dark‐induced inactivation of some PSII reaction centers that was accompanied by a decrease in the flux of electrons to PSI. Darkness induced the plastoquinone‐reductase activity associated with chlororespiration and the phosphorylation of light harvesting complex (LHC). We propose that upon phosphorylation the LHC detaches from PSII, resulting in a decrease of exciton‐trapping by PSII reaction centers and, consequently, an increased dissipation of light energy. This mechanism probably serves an ecophysiological function in lichens to prevent the damage at dawn or under strong fluctuating light conditions when lichens are in a hydrated state.

Transcriptome Profiling of Bigelowiella natans in Response to Light Stress.

Bigelowiella natans is a marine chlorarachniophyte whose plastid was acquired secondarily via endosymbiosis with a green alga. During plastid evolution, the photosynthetic endosymbiont would have integrated with the host metabolic pathways. This would require the evolution and coordination of strategies to cope with changes in light intensity that includes changes in the expression of both endosymbiont and host-derived genes. To investigate the transcriptional response to light intensity in chlorarachniophytes, we conducted an RNA-seq experiment to identify differentially expressed genes following a 4-h shift to high or very-low light. A shift to high light altered the expression of over 2,000 genes, many involved with photosynthesis, PSII assembly, primary metabolism, and reactive-oxygen scavenging. These changes are an attempt to optimize photosynthesis and increase energy sinks for excess reductant, while minimizing photooxidative stress. A transfer to very-low light resulted in a lower photosynthetic performance and metabolic alteration, reflecting an energy-limited state. Genes located on the nucleomorph, the vestigial nucleus in the plastid, had few changes in expression in either light treatment, indicating this organelle has relinquished most transcriptional control to the nucleus. Overall, during plastid origin, both host and transferred endosymbiont genes evolved a harmonized transcriptional network to respond to a classic photosynthetic stress.

Chemical quenching of singlet oxygen by plastoquinols and their oxidation products in Arabidopsis.

Prenylquinols (tocochromanols and plastoquinols) serve as efficient physical and chemical quenchers of singlet oxygen (1 O2 ) formed during high light stress in higher plants. Although quenching of 1 O2 by prenylquinols has been previously studied, direct evidence for chemical quenching of 1 O2 by plastoquinols and their oxidation products is limited invivo. In the present study, the role of plastoquinol-9 (PQH2 -9) in chemical quenching of 1 O2 was studied in Arabidopsis thaliana lines overexpressing the SOLANESYL DIPHOSPHATE SYNTHASE 1 gene (SPS1oex) involved in PQH2 -9 and plastochromanol-8 biosynthesis. In this work, direct evidence for chemical quenching of 1 O2 by plastoquinols and their oxidation products is presented, which is obtained by microscopic techniques invivo. Chemical quenching of 1 O2 was associated with consumption of PQH2 -9 and formation of its various oxidized forms. Oxidation of PQH2 -9 by 1 O2 leads to plastoquinone-9 (PQ-9), which is subsequently oxidized to hydroxyplastoquinone-9 [PQ(OH)-9]. We provide here evidence that oxidation of PQ(OH)-9 by 1 O2 results in the formation of trihydroxyplastoquinone-9 [PQ(OH)3 -9]. It is concluded here that PQH2 -9 serves as an efficient 1 O2 chemical quencher in Arabidopsis, and PQ(OH)3 -9 can be considered as a natural product of 1 O2 reaction with PQ(OH)-9. The understanding of the mechanisms underlying 1 O2 chemical quenching provides information on the role of plastoquinols and their oxidation products in the response of plants to photooxidative stress.

The plastoquinone pool outside the thylakoid membrane serves in plant photoprotection as a reservoir of singlet oxygen scavengers.

The Arabidopsis vte1 mutant is devoid of tocopherol and plastochromanol (PC-8). When exposed to excess light energy, vte1 produced more singlet oxygen (1 O2 ) and suffered from extensive oxidative damage compared with the wild type. Here, we show that overexpressing the solanesyl diphosphate synthase 1 (SPS1) gene in vte1 induced a marked accumulation of total plastoquinone (PQ-9) and rendered the vte1 SPS1oex plants tolerant to photooxidative stress, indicating that PQ-9 can replace tocopherol and PC-8 in photoprotection. High total PQ-9 levels were associated with a noticeable decrease in 1 O2 production and higher levels of Hydroxyplastoquinone (PQ-C), a 1 O2 -specific PQ-9 oxidation product. The extra PQ-9 molecules in the vte1 SPS1oex plants were stored in the plastoglobules and the chloroplast envelopes, rather than in the thylakoid membranes, whereas PQ-C was found almost exclusively in the thylakoid membranes. Upon exposure of wild-type plants to high light, the thylakoid PQ-9 pool decreased, whereas the extrathylakoid pool remained unchanged. In vte1 and vte1 SPS1oex plants, the PQ-9 losses in high light were strongly amplified, affecting also the extrathylakoid pool, and PQ-C was found in high amounts in the thylakoids. We conclude that the thylakoid PQ-9 pool acts as a 1 O2 scavenger and is replenished from the extrathylakoid stock.

Probiotic fermentation augments the skin anti-photoaging properties of Agastache rugosa through up-regulating antioxidant components in UV-B-irradiated HaCaT keratinocytes

BackgroundAgastache rugosa (Fisch. & C.A.Mey.) Kuntze (Korean mint) is used to treat diverse types of human disorders in traditional medicine. In recent years, its non-fermented leaf extract (ARE) has been shown to possess protective properties against ultraviolet-B (UV-B) radiation-induced photooxidative stress. The present work aimed to examine whether probiotic bacterial fermentation would potentiate the skin anti-photoaging activity of ARE or not, by comparing the protective properties of ARE and corresponding fermented extract (ARE-F) against UV-B radiation-induced photooxidative stress in HaCaT keratinocytes.MethodsARE-F was produced from ARE by the fermentation with Lactobacillus rhamnosus HK-9, a type of Gram-positive probiotic bacterial strain. Anti-photoaging activities were evaluated by analyzing reactive oxygen species (ROS), promatrix metalloproteinases (proMMPs), total glutathione (GSH) and total superoxide dismutase (SOD) in UV-B-irradiated HaCaT keratinocytes. Antiradical activity was determined using 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging assay.ResultsARE-F contained higher attenuating activity on the UV-B-induced ROS generation than ARE. Similarly, ARE-F was able to diminish the UV-B-induced proMMP-9 and -2 more effectively than ARE. ARE-F displayed higher tendencies to augment the UV-B-reduced total GSH content and SOD activity than ARE. However, there were no significant difference between ARE and ARE-F in ABTS radical scavenging activities.ConclusionsThe findings suggest that the UV-B radiation-protective activity of ARE is enhanced by probiotic bacterial fermentation, which might improve the therapeutic and cosmetic values of A. rugosa leaves.

Depth related adaptations in symbiont bearing benthic foraminifera: New insights from a field experiment on Operculina ammonoides

Large benthic foraminifera (LBF) are marine calcifying protists that commonly harbor algae as symbionts. These organisms are major calcium carbonate producers and important contributors to primary production in the photic zones. Light is one of the main known factors limiting their distribution, and species of this group developed specific mechanisms that allow them to occupy different habitats across the light gradient. Operculina ammonoides (Gronovius, 1781) is a planispiral LBF that has two main shell morphotypes, thick involute and flat evolute. Earlier studies suggested morphologic changes with variation in water depth and presumably light. In this study, specimens of the two morphotypes were placed in the laboratory under artificial low light and near the sea floor at depths of 15 m, 30 m, and 45 m in the Gulf of Aqaba-Eilat for 23 days. Differences in growth and symbionts content were evaluated using weight, size, and chlorophyll a. Our results show that O. ammonoides exhibit morphological plasticity when constructing thinner chambers after relocation to low light conditions, and adding more weight per area after relocation to high light conditions. In addition, O. ammonoides exhibited chlorophyll content adaptation to a certain range of light conditions, and evolute specimens that were acclimatized to very low light did not survive relocation to a high light environment, possibly due to photo-oxidative stress.