Antioxidants, Oxidative Damage and Oxygen Deprivation Stress: a Review

Microalgae represent an exceptionally diverse but highly specialized group of micro-organisms adapted to various ecological habitats. Many microalgae have the ability to produce substantial amounts (e.g. 20-50% dry cell weight) of triacylglycerols (TAG) as a storage lipid under photo-oxidative stress or other adverse environmental conditions. Fatty acids, the building blocks for TAGs and all other cellular lipids, are synthesized in the chloroplast using a single set of enzymes, of which acetyl CoA carboxylase (ACCase) is key in regulating fatty acid synthesis rates. However, the expression of genes involved in fatty acid synthesis is poorly understood in microalgae. Synthesis and sequestration of TAG into cytosolic lipid bodies appear to be a protective mechanism by which algal cells cope with stress conditions, but little is known about regulation of TAG formation at the molecular and cellular level. While the concept of using microalgae as an alternative and renewable source of lipid-rich biomass feedstock for biofuels has been explored over the past few decades, a scalable, commercially viable system has yet to emerge. Today, the production of algal oil is primarily confined to high-value specialty oils with nutritional value, rather than commodity oils for biofuel. This review provides a brief summary of the current knowledge on oleaginous algae and their fatty acid and TAG biosynthesis, algal model systems and genomic approaches to a better understanding of TAG production, and a historical perspective and path forward for microalgae-based biofuel research and commercialization.

https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1365-313X.2008.03492.x

Microalgal triacylglycerols as feedstocks for biofuel production: perspectives and advances

Cold, salinity and drought stresses: an overview.

Water deficits cause a reduction in the rate of photosynthesis. Exposure to mild water deficits, when relative water content (RWC) remains above 70%, primarily causes limitation to carbon dioxide uptake because of stomatal closure. With greater water deficits, direct inhibition of photosynthesis occurs. In both cases limitation of carbon dioxide fixation results in exposure of chloroplasts to excess excitation energy. Much of this can be dissipated by various photoprotective mechanisms. These include dissipation as heat via carotenoids, photorespiration, CAM idling and, in some species, leaf movements and other morphological features which minimize light absorption. The active oxygen species superoxide and singlet oxygen are produced in chloroplasts by photoreduction of Oxygen and energy transfer from triplet excited chlorophyll to oxygen, respectively. Hydrogen peroxide and hydroxyl radicals can form as a result of the reactions of superoxide. All these species are reactive and potentially damaging, causing lipid peroxidation and inactivation of enzymes. They are normally scavenged by a range of antioxidants and enzymes which are present in the chloroplast and other subcellular compartments. When carbon dioxide fixation is limited by water deficit, the rate of active oxygen formation increases in chloroplasts as excess excitation energy, not dissipated fay the photoprotective mechanisms, is used to form superoxide and singlet oxygen. However, photorespiratory hydrogen peroxide production in peroxisomes decreases. Increased superoxide can be detected by EPR (electron paramagnetic resonance) in chloroplasts from droughted plants. Stiperoxide formation leads to changes suggestive of oxidative damage including lipid peroxidation and a decrease in ascorbate. These changes are not, however, apparent until severe water deficits develop, and they could also be interpreted as secondary effects of water deficit-induced senescence or wounding. Non-lethal water deficits often result in increased activity of superoxide dismutase, glutathione reductase and monodehydroascorbate reductase. Increased capacity of these protective enzymes may be part of a general antioxidative response in plants involving regulation of protein synthesis or gene expression. Since the capacity of these enzymes is also increased by other treatments which cause oxidative damage, and which alter the balance between excitation energy input and carbon dioxide fixation such as low temperature and high irradiance, it is suggested that water deficit has the same effect. Light levels that are not normally excessive do become excessive and photoprotective/antioxidative systems are activated. Some of the photoprotective mechanisms themselves could result in active oxygen formation. Photoinhibitory damage also includes a component of oxidative damage. During normally-encountered degrees of water deficit the capacity of the antioxidant systems and their ability to respond to increased active oxygen generation may be sufficient to prevent overt expression of damage. Desiccation-tolerant tissues such as bryophytes, lichens, spores, seeds, some algae and a few vascular plant leaves can survive desiccation to below 30-40% RWC, A component of desiccation damage in seeds and bacteria is oxygen-dependent. Desiccation causes oxidation of glutathione, a major antioxidant, and appearance of a free radical signal detected by EPR in a number of tissues suggesting that oxidative damage has occurred. In photosynthetic cells damage may arise from photooxidation. Disruption of membrane-bound electron tranport systems in partially hydrated tissue could lead to reduction of oxygen to superoxide. Oxidation of lipids and sulphydryl groups may also occur in dry tissue. Tolerant cells recover upon rehydration and arc able to reduce their glutathione pool. Non-tolerant species go on to show further oxidative damage including lipid peroxidation. It is difficult to attribute this subsequent damage to the cause or effect of death. Embryos in seeds lose desiccation tolerance soon after imbibition. This is associated with membrane damage that has been attributed to superoxide-mediated deesterification of phospholipids and loss of lipophilic antioxidants. These effects are discussed in relation to other mechanisms involved in desiccation tolerance. Contents Summary 27 I. Introduction 28 II. Generation of active oxygen and defence mechanisms in plant cells 29 III. The effect of water deficit on photosynthesis 31 IV. Mechanisms for active oxygen generation during water deficit 36 V. Evidence for oxidative damage during water deficit 39 VI. Desiccation 47 VII. Conclusions 52 Acknowledgements 53 References 53.

The role of active oxygen in the response of plants to water deficit and desiccation.

Phosphatidic acid (PtdOH) is emerging as an important signalling lipid in abiotic stress responses in plants. The effect of cold stress was monitored using 32P-labelled seedlings and leaf discs of Arabidopsis thaliana. Low, non-freezing temperatures were found to trigger a very rapid 32P-PtdOH increase, peaking within 2 and 5 min, respectively. In principle, PtdOH can be generated through three different pathways, i.e. i) via de novo phospholipid biosynthesis (through acylation of lyso-PtdOH), ii) via phospholipase D hydrolysis of structural phospholipids or iii) via phosphorylation of diacylglycerol (DAG) by DAG kinase (DGK). Using a differential 32P-labelling protocol and a PLD-transphosphatidylation assay, evidence is provided that the rapid 32P-PtdOH response was primarily generated through DGK. A simultaneous decrease in the levels of 32P-PtdInsP, correlating in time, temperature dependency and magnitude with the increase in 32P-PtdOH, suggested that a PtdInsP-hydrolyzing PLC generated the DAG in this reaction. Testing T-DNA insertion lines available for the seven DGK genes, revealed no clear changes in 32P-PtdOH responses, suggesting functional redundancy. Similarly, known cold-stress mutants were analyzed to investigate whether the PtdOH response acted downstream of the respective gene products. The hos1, los1 and fry1 mutants were found to exhibit normal PtdOH responses. Slight changes were found for ice1, snow1, and the overexpression line Super-ICE1, however, this was not cold-specific and likely due to pleiotropic effects. A tentative model illustrating direct cold effects on phospholipid metabolism is presented.

/pdf/rapid-phosphatidic-acid-accumulation-in-response-to-low-3xktru1vuv.pdf

Rapid phosphatidic acid accumulation in response to low temperature stress in Arabidopsis is generated through diacylglycerol kinase

Eukaryotic organisms as well as some prokaryotes and viruses contain sphingolipids, which are defined by a common structural feature, i.e. , a "sphingoid base" backbone such as D-erythro-1,3-dihydroxy, 2-aminooctadec-4-ene (sphingosine). The sphingolipids of mammalian tissues, lipoproteins, and milk include ceramides, sphingomyelins, cerebrosides, gangliosides and sulfatides; plants, fungi and yeast have mainly cerebrosides and phosphoinositides. The total amounts of sphingolipids in food vary considerably, from a few micromoles per kilogram (fruits) to several millimoles per kilogram in rich sources such as dairy products, eggs and soybeans. With the use of the limited data available, per capita sphingolipid consumption in the United States can be estimated to be on the order of 150-180 mmol (approximately 115-140 g) per year, or 0.3-0.4 g/d. There is no known nutritional requirement for sphingolipids; nonetheless, they are hydrolyzed throughout the gastrointestinal tract to the same categories of metabolites (ceramides and sphingoid bases) that are used by cells to regulate growth, differentiation, apoptosis and other cellular functions. Studies with experimental animals have shown that feeding sphingolipids inhibits colon carcinogenesis, reduces serum LDL cholesterol and elevates HDL, suggesting that sphingolipids represent a "functional" constituent of food. Sphingolipid metabolism can also be modified by constituents of the diet, such as cholesterol, fatty acids and mycotoxins (fumonisins), with consequences for cell regulation and disease. Additional associations among diet, sphingolipids and health are certain to emerge as more is learned about these compounds.

/pdf/sphingolipids-in-food-and-the-emerging-importance-of-21zopq8qbz.pdf

Sphingolipids in Food and the Emerging Importance of Sphingolipids to Nutrition

In 1991, a novel robot, MIT-MANUS, was introduced to study the potential that robots might assist in and quantify the neuro-rehabilitation of motor function. MIT-MANUS proved an excellent tool for shoulder and elbow rehabilitation in stroke patients, showing in clinical trials a reduction of impairment in movements confined to the exercised joints. This successful proof of principle as to additional targeted and intensive movement treatment prompted a test of robot training examining other limb segments. This paper focuses on a robot for wrist rehabilitation designed to provide three rotational degrees-of-freedom. The first clinical trial of the device will enroll 200 stroke survivors. Ultimately 160 stroke survivors will train with both the proximal shoulder and elbow MIT-MANUS robot, as well as with the novel distal wrist robot, in addition to 40 stroke survivor controls. So far 52 stroke patients have completed the robot training (ongoing protocol). Here, we report on the initial results on 36 of these volunteers. These results demonstrate that further improvement should be expected by adding additional training to other limb segments.

Robot-Aided Neurorehabilitation: A Robot for Wrist Rehabilitation

Lipid composition and thermotropic phase behavior of boar, bull, stallion, and rooster sperm membranes.

Background
Previous results with the planar robot MIT-MANUS demonstrated positive benefits in trials with over 250 stroke patients. Consistent with motor learning, the positive effects did not generalize to other muscle groups or limb segments. Therefore we are designing a new class of robots to exercise other muscle groups or limb segments. This paper presents basic engineering aspects of a novel robotic module that extends our approach to anti-gravity movements out of the horizontal plane and a pilot study with 10 outpatients. Patients were trained during the initial six-weeks with the planar module (i.e., performance-based training limited to horizontal movements with gravity compensation). This training was followed by six-weeks of robotic therapy that focused on performing vertical arm movements against gravity. The 12-week protocol includes three one-hour robot therapy sessions per week (total 36 robot treatment sessions).

/pdf/rehabilitation-robotics-pilot-trial-of-a-spatial-extension-35dc13avd7.pdf

Rehabilitation robotics: pilot trial of a spatial extension for MIT-Manus

Highly enriched plasma membrane fractions were isolated from leaves of nonacclimated (NA) and acclimated (ACC) rye (Secale cereale L. cv Puma) seedlings. Collectively, free sterols, steryl glucosides, and acylated steryl glucosides constituted >50 mole% of the total lipid in both NA and ACC plasma membrane fractions. Glucocerebrosides containing hydroxy fatty acids constituted the major glycolipid class of the plasma membrane, accounting for 16 mole% of the total lipid. Phospholipids, primarily phosphatidylcholine and phosphatidylethanolamine with lesser amounts of phosphatidylglycerol, phosphatidic acid, phosphatidylserine, and phosphatidylinositol, comprised only 32 mole% of the total lipid in NA samples. Following cold acclimation, free sterols increased from 33 to 44 mole%, while steryl glucosides and acylated steryl glucosides decreased from 15 to 6 mole% and 4 to 1 mole%, respectively. Sterol analyses of these lipid classes demonstrated that free beta-sitosterol increased from 21 to 32 mole% (accounting for the increase in free sterols as a class) at the expense of sterol derivatives containing beta-sitosterol. Glucocerebrosides decreased from 16 to 7 mole% of the total lipid following cold acclimation. In addition, the relative proportions of associated hydroxy fatty acids, including 22:0 (h), 24:0 (h), 22:1 (h), and 24:1 (h), were altered. The phospholipid content of the plasma membrane fraction increased to 42 mole% of the total lipid following cold acclimation. Although the relative proportions of the individual phospholipids did not change appreciably after cold acclimation, there were substantial differences in the molecular species. Di-unsaturated molecular species (18:2/18:2, 18:2/18:3, 18:3/18:3) of phosphatidylcholine and phosphatidylethanolamine increased following acclimation. These results demonstrate that cold acclimation results in substantial changes in the lipid composition of the plasma membrane.

Daniel V. Lynch

Papers

Sphingolipids in Food and the Emerging Importance of Sphingolipids to Nutrition

Robot-Aided Neurorehabilitation: A Robot for Wrist Rehabilitation

Lipid composition and thermotropic phase behavior of boar, bull, stallion, and rooster sperm membranes.

Rehabilitation robotics: pilot trial of a spatial extension for MIT-Manus

Plasma Membrane Lipid Alterations Associated with Cold Acclimation of Winter Rye Seedlings (Secale cereale L. cv Puma)