RESPONSE OF THE WILD-TYPE and HIGH LIGHT-TOLERANT MUTANT OF Anacystis nidulans AGAINST PHOTOOXIDATIVE DAMAGE: DIFFERENTIAL MECHANISM OF HIGH LIGHT TOLERANCE (original) (raw)
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Coral Reefs, 2015
During the last decades, coral reefs have been affected by several large-scale bleaching events, and such phenomena are expected to increase in frequency and severity in the future, thus compromising their survival. High sea surface temperature accompanied by high levels of solar irradiance has been found to be responsible for the induction of oxidative stress ultimately ending with the disruption of the symbiosis between cnidarians and Symbiodinium. For two decades, many studies have pointed to the water-water cycle (WWC) as being one of the primary mediators of this phenomenon, but the impacts of environmental stress on the O 2 reduction by PSI and the associated reactive oxygen species (ROS)-detoxifying enzymes remain to be determined. In this study, we analyzed the impacts of acute thermal and light stress on the WWC in the model Symbiodinium strain A1. We observed that the high light treatment at 26°C resulted in the upregulation of superoxide dismutase, ascorbate peroxidase, and glutathione reductase activities and an increased production of ROS with no significant change in O 2-dependent electron transport. Under high light and at 33°C, O 2-dependent electron transport was significantly increased relative to total electron transport. This increase was concomitant with a twofold increase in ROS generation compared with the treatment at 26°C, while enzymes involved in the WWC were largely inactivated. These data show for the first time that combined heat and light stress inactivate antioxidant capacities of the WWC and suggests that its photoprotective functions are overwhelmed under these conditions. This study also indicates that cnidarians may be more prone to bleach if they harbor Symbiodinium cells having a highly active Mehler-type electron transport, unless they are able to quickly up-regulate their antioxidant capacities.
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2014
Roles of oxidative stress and photoinhibition in high light acclimation were studied using a regulatory mutant of the cyanobacterium Synechocystis sp. PCC 6803. The mutant strain ΔsigCDE contains the stress responsive SigB as the only functional group 2 σ factor. The ΔsigCDE strain grew more slowly than the control strain in methylviologen-induced oxidative stress. Furthermore, a fluorescence dye detecting H 2 O 2 , hydroxyl and peroxyl radicals and peroxynitrite, produced a stronger signal in ΔsigCDE than in the control strain, and immunological detection of carbonylated residues showed more protein oxidation in ΔsigCDE than in the control strain. These results indicate that ΔsigCDE suffers from oxidative stress in standard conditions. The oxidative stress may be explained by the findings that ΔsigCDE had a low content of glutathione and low amount of Flv3 protein functioning in the Mehler-like reaction. Although ΔsigCDE suffers from oxidative stress, up-regulation of photoprotective carotenoids and Flv4, Sll2018, Flv2 proteins protected PSII against light induced damage by quenching singlet oxygen more efficiently in ΔsigCDE than in the control strain in visible and in UV-A/B light. However, in UV-C light singlet oxygen is not produced and PSII damage occurred similarly in the ΔsigCDE and control strains. According to our results, resistance against the light-induced damage of PSII alone does not lead to high light tolerance of the cells, but in addition efficient protection against oxidative stress would be required.
Photooxidative damage to the cyanobacterium Spirulina platensis mediated by singlet oxygen
Current Microbiology, 1995
Experiments on the specific growth rate, bleaching of pigments, O2 evolution, lipid peroxidation, and loss of sulfhydryl (-SH) content in response to the varying light intensities (2–28 W/m2) suggested that photodamage to the Spirulina cells was maximum at or beyond the photosynthesis saturating light intensity (12 W/m2). However, photobleaching of the chlorophyll a was relatively higher than β carotenoid. The results on the N,N-dimethyl-p-nitrosoaniline (RNO) bleaching in the presence of oxygen radical quenchers exhibited maximum effect of sodium azide and indicated about the generation of singlet oxygen. The chlorophyll a-sensitized production of singlet oxygen by a type II reaction cannot be ruled out because of maximum oxidative damage to the cells at or beyond the photosynthesis saturating light intensity, i.e., 12 W/m2, when the availability of triplet chlorophyll is maximum.
Detailed analysis of reactive oxygen species induced by visible light in various cell types
Lasers in Surgery and Medicine, 2010
Background and ObjectiveLight in the visible and near infrared region stimulates various cellular processes, and thus has been used for therapeutic purposes. One of the proposed mechanisms is based on cellular production of reactive oxygen species (ROS) in response to illumination. In the present study, we followed visible light (VL)-induced hydroxyl radicals in various cell types and cellular sites using the electron paramagnetic resonance (EPR) spin-trapping technique.Light in the visible and near infrared region stimulates various cellular processes, and thus has been used for therapeutic purposes. One of the proposed mechanisms is based on cellular production of reactive oxygen species (ROS) in response to illumination. In the present study, we followed visible light (VL)-induced hydroxyl radicals in various cell types and cellular sites using the electron paramagnetic resonance (EPR) spin-trapping technique.Materials and MethodsFibroblasts, sperm cells, cardiomyocytes, and skeletal muscle cells were irradiated with broadband (400–800 nm) VL. To detect ROS, the EPR spin-trapping technique coupled with the spin-traps 5,5-dimethyl pyrroline-N-oxide (DMPO) or 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide (DEPMPO) were used. To investigate the cellular sites of ROS formation, the cell-permeable molecule, isopropanol, or the nonpermeable proteins, bovine serum albumin (BSA) and superoxide dismutase (SOD), were introduced to the cells before irradiation. ROS production in mitochondria was measured using the fluorescent probe, MitoTracker Red (MTR).Fibroblasts, sperm cells, cardiomyocytes, and skeletal muscle cells were irradiated with broadband (400–800 nm) VL. To detect ROS, the EPR spin-trapping technique coupled with the spin-traps 5,5-dimethyl pyrroline-N-oxide (DMPO) or 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide (DEPMPO) were used. To investigate the cellular sites of ROS formation, the cell-permeable molecule, isopropanol, or the nonpermeable proteins, bovine serum albumin (BSA) and superoxide dismutase (SOD), were introduced to the cells before irradiation. ROS production in mitochondria was measured using the fluorescent probe, MitoTracker Red (MTR).Results and ConclusionsThe concentration of .OH increased both with illumination time and with cell concentration, and decreased when N2 was bubbled into the cell culture, suggesting that VL initiates a photochemical reaction via endogenous photosensitizers. VL was found to stimulate ROS generation both in membrane and cytoplasm. In addition, fluorescent measurments confirmed the mitochondria to be target for light–cell interaction. The findings support the hypothesis that ROS are generated in various cellular sites following light illumination. Lasers Surg. Med. 42:473–480, 2010. © 2010 Wiley–Liss, Inc.The concentration of .OH increased both with illumination time and with cell concentration, and decreased when N2 was bubbled into the cell culture, suggesting that VL initiates a photochemical reaction via endogenous photosensitizers. VL was found to stimulate ROS generation both in membrane and cytoplasm. In addition, fluorescent measurments confirmed the mitochondria to be target for light–cell interaction. The findings support the hypothesis that ROS are generated in various cellular sites following light illumination. Lasers Surg. Med. 42:473–480, 2010. © 2010 Wiley–Liss, Inc.
A Possible Physiological Function of the Oxygen-Photoreducing System of Rhodospirillum Rubrum
Archives of …, 1976
Anaerobic suspensions of Rhodospirillum rubrum cells which had been grown in the dark under low oxygen tension showed only a small increase of their ATP content when illuminated for 30 s. The same suspensions failed to start immediate growth in the light. Both high light-induced ATP levels and immediate phototrophic growth were elicited by small amounts of oxygen which were insufficient by themselves to raise the ATP levels or to support growth in the dark. The oxygen requirement for growth disappeared after some time of anaerobic illumination and was not observed in suspensions of cells which had been grown in the light under anaerobiosis. Furthermore, these phototrophic cells reached the maximum levels of ATP when illuminated in the absence of oxygen. Strain F11, a mutant derivative of Rhodospirillum rubrum which lacked the ability to photoreduce oxygen in vitro, needed abnormally high amounts of oxygen to increase its ATP levels and to grow in the light. Besides, KCN inhibited the increase of ATP levels in illuminated mutant cells but not in wild type cells. An additional difference between both strains was that the oxygen requirement for growth did not disappear in the mutant after some time of anaerobic incubation in the light. To explain these observations, it is proposed that the photosynthetic system of semiaerobically-grown Rhodospirillum rubrum becomes overreduced under anaerobiosis. The oxygen-photoreducing system, which is impaired in the mutant, is apparently used to oxidize the photosynthetic system to its optimal redox state, carrying electrons to oxygen or to other endogenous acceptors which are formed during incubation in the light. The mutant seems to replace the defective system by a cyanide-sensitive pathway which may reduce oxygen but not the alternative endogenous acceptors.
Oxidative stress inhibits the repair of photodamage to the photosynthetic machinery
EMBO Journal, 2001
Absorption of excess light energy by the photosynthetic machinery results in the generation of reactive oxygen species (ROS), such as H 2 O 2. We investigated the effects in vivo of ROS to clarify the nature of the damage caused by such excess light energy to the photosynthetic machinery in the cyanobacterium Synechocystis sp. PCC 6803. Treatments of cyanobacterial cells that supposedly increased intracellular concentrations of ROS apparently stimulated the photodamage to photosystem II by inhibiting the repair of the damage to photosystem II and not by accelerating the photodamage directly. This conclusion was con®rmed by the effects of the mutation of genes for H 2 O 2-scavenging enzymes on the recovery of photosystem II. Pulse labeling experiments revealed that ROS inhibited the synthesis of proteins de novo. In particular, ROS inhibited synthesis of the D1 protein, a component of the reaction center of photosystem II. Northern and western blot analyses suggested that ROS might in¯uence the outcome of photodamage primarily via inhibition of translation of the psbA gene, which encodes the precursor to D1 protein. Keywords: cyanobacterium/D1 protein/H 2 O 2-scavenging enzyme/photosystem II/reactive oxygen species
Singlet oxygen and free radical production during acceptor- and donor-side-induced photoinhibition
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1994
High-intensity illumination of thylakoids results in the well-characterized impairment of Photosystem II electron transport (photoinhibition), followed by the degradation of the D1 reaction centre protein. The time-course and features of photodamage are different in fully functional thylakoid membranes, when photoinhibition is invoked by impairment of Photosystem II acceptor side electron transport, and in thylakoids which are unable to oxidize water, when the damage is a consequence of inactivation of Photosystem II donor side (reviewed by Aro, E.-M., Virgin, I. and Andersson, B. (1993) Biochim. Biophys. Acta 1134, 113-134).
2006
We studied the effects of highlight exposure (500 pmol m-'s-' of photosynthetic active radiation) on the cyanobacteria Nostoc spongiaeforme Agardh, a freshwater alga, and Phonnidium corium Agardh (Gomont), a marine alga, with respect to photosynthesis, pigments, sugar content, lipid peroxidation, fatty acids composition, antioxidant enzymes activity and DNA. It was seen that the ratio of variable fluorescence (Fk) to maximum fluorescence (Fm), which is indicative of photosynthetic efficiency, decreased because of the light treatment. The damage to photosynthesis occurred in the antenna system and the photosynthetic II reaction center. Photobleaching of photosynthetic pigments was also observed. Highlight treatment also resulted in decreased sugar content, which was probably due to the effect on photosynthesis. Peroxidation of membrane lipids, indicating oxidative damage to lipids and a high level of unsaturation in the cell membrane, was also observed. The activity of antioxidant enzyme superoxide dismutase and ascorbate peroxidase was increased, probably as a result of oxidative damage observed in the form of lipid peroxidation. Quantitative decreases in phospholipid and glycolipid levels were also observed. The level of unsaturated fatty acids in total lipids and glycolipids remained unchanged in both species; however, the level of saturated fatty acids decreased, which slightly changed the ratio in favor of unsaturated fatty acids. Degradation of DNA was also observed in both species. There was a transient plateau 2-4 h after exposure to highlight treatment in the Fv/Fm ratio and in levels of phycobilisome pigments, sugars and antioxidant enzymes after an initial decrease 1 h after the treatment. These findings may indicate a period of partial adaptation to high light that is due to the efficiency of protective processes operational in the two species, which subsequently failed after a longer exposure duration of 4-6 h.