University of Kentucky

About: University of Kentucky is a education organization based out in Lexington, Kentucky, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 43933 authors who have published 92195 publications receiving 3256087 citations. The organization is also known as: UK.

Evidence Supporting a Role of Jasmonic Acid in Arabidopsis Leaf Senescence

Abstract: In this work, the role of jasmonic acid (JA) in leaf senescence is examined. Exogenous application of JA caused premature senescence in attached and detached leaves in wild-type Arabidopsis but failed to induce precocious senescence of JA-insensitive mutant coi1 plants, suggesting that the JA-signaling pathway is required for JA to promote leaf senescence. JA levels in senescing leaves are 4-fold higher than in non-senescing ones. Concurrent with the increase in JA level in senescing leaves, genes encoding the enzymes that catalyze most of the reactions of the JA biosynthetic pathway are differentially activated during leaf senescence in Arabidopsis, except for allene oxide synthase , which is constitutively and highly expressed throughout leaf development. Arabidopsis lipoxygenase 1 (cytoplasmic) expression is greatly increased but lipoxygenase 2 (plastidial) expression is sharply reduced during leaf senescence. Similarly, AOC1 ( allene oxide cyclase 1 ), AOC2 , and AOC3 are all up-regulated, whereas AOC4 is down-regulated with the progression of leaf senescence. The transcript levels of 12-oxo-PDA reductase 1 and 12-oxo-PDA reductase 3 also increase in senescing leaves, as does PED1 (encoding a 3-keto-acyl-thiolase for β-oxidation). This represents the first report, to our knowledge, of an increase in JA levels and expression of oxylipin genes during leaf senescence, and indicates that JA may play a role in the senescence program.

Superoxide dismutases and superoxide reductases

Abstract: Superoxide, O2•–, is formed in all living organisms that come in contact with air, and, depending upon its biological context, it may act as a signaling agent, a toxic species, or a harmless intermediate that decomposes spontaneously Its levels are limited in vivo by two different types of enzymes, superoxide reductase (SOR) and superoxide dismutase (SOD) Although superoxide has long been an important factor in evolution, it was not so when life first emerged on Earth at least 35 billion years ago At that time, the early biosphere was highly reducing and lacking in any significant concentrations of dioxygen (O2), very different from what it is today Consequently, there was little or no O2•– and therefore no reason for SOR or SOD enzymes to evolve Instead, the history of biological O2•– probably commences somewhere around 24 billion years ago, when the biosphere started to experience what has been termed the “Great Oxidation Event”, a transformation driven by the increase in O2 levels, formed by cyanobacteria as a product of oxygenic photosynthesis1 The rise of O2 on Earth caused a reshaping of existing metabolic pathways, and it triggered the development of new ones2 Its appearance led to the formation of the so-called “reactive oxygen species” (ROS), for example, superoxide, hydrogen peroxide, and hydroxyl radical, and to a need for antioxidant enzymes and other antioxidant systems to protect against the growing levels of oxidative damage to living systems Dioxygen is a powerful four-electron oxidizing agent, and the product of this reduction is water 1 When O2 is reduced in four sequential one-electron steps, the intermediates formed are the three major ROS, that is, O2•–, H2O2, and HO• 2 3 4 5 Each of these intermediates is a potent oxidizing agent The consequences of their presence to early life must have been an enormous evolutionary challenge In the case of superoxide, we find the SOD and SOR enzymes to be widely distributed throughout current living organisms, both aerobic and anaerobic, suggesting that, from the start of the rise of O2 on Earth, the chemistry of superoxide has been an important factor during evolution The SORs and three very different types of SOD enzymes are redox-active metalloenzymes that have evolved entirely independently from one another for the purpose of lowering superoxide concentrations SORs catalyze the one-electron reduction of O2•– to give H2O2, a reaction requiring two protons per superoxide reacted as well as an external reductant to provide the electron (eq 6) SODs catalyze the disproportionation of superoxide to give O2 and H2O2, a reaction requiring one proton per superoxide reacted, but no external reductant (eq 7) 6 7 All of the SOR enzymes contain only iron, while the three types of SODs are the nickel-containing SODs (NiSOD), the iron- or manganese-containing SODs (FeSOD and MnSOD), and the copper- and zinc-containing SODs (CuZnSOD) Although the structures and other properties of these four types of metalloenzymes are quite different, they all share several characteristics, including the ability to react rapidly and selectively with the small anionic substrate O2•– Consequently, there are some striking similarities between these otherwise dissimilar enzymes, many of which can be explained by considering the nature of the chemical reactivity of O2•– (see below) Numerous valuable reviews describing the SOD and SOR enzymes have appeared over the years, but few have covered and compared all four classes of these enzymes, as we attempt to do here Thus, the purpose of this Review is to describe, compare, and contrast the properties of the SOR and the four SOD enzymes; to summarize what is known about their evolutionary pathways; and to analyze the properties of these enzymes in light of what is known of the inherent chemical reactivity of superoxide

Elevated thiobarbituric acid-reactive substances and antioxidant enzyme activity in the brain in Alzheimer's disease

Abstract: We determined levels of thiobarbituric acid-reactive substances (TBARS), a measure of lipid peroxidation, and the activity of the antioxidant enzymes superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), glutathione reductase (GSSG-R), and catalase (CAT) in the amygdala, hippocampus, pyriform cortex, superior and middle temporal gyri, inferior parietal lobule, middle frontal gyrus, occipital pole, and cerebellum of 13 Alzheimer's disease (AD) and 10 control brains. Levels of TBARS were elevated in all AD brain regions except the middle frontal gyrus, and elevation levels reached statistical significance in the hippocampus and pyriform cortex and marginal significance in the amygdala of AD subjects compared with age-matched controls. Significant elevation of GSH-Px activity was present in AD hippocampus compared with control. Moderate but statistically insignificant elevations of GSH-Px activity also were present in the amygdala and pyriform cortex in AD. GSSG-R activity was significantly elevated in the amygdala and hippocampus in AD subjects compared with controls. CAT activity was significantly elevated in AD hippocampus and superior and middle temporal gyri. SOD levels were elevated in all brain regions in AD patients compared with controls, although none of these elevations reached statistical significance. Antioxidant enzyme activities were significantly elevated where lipid peroxidation was most pronounced, suggesting a compensatory rise in antioxidant activity in response to increased free radical formation. This study supports the concept that the brain in AD is under increased oxidative stress and demonstrates that the oxidative changes are most pronounced in the medial temporal lobe, where histopathologic alterations are most severe.

Herbivores and nutrients control grassland plant diversity via light limitation

Abstract: Human alterations to nutrient cycles and herbivore communities are affecting global biodiversity dramatically. Ecological theory predicts these changes should be strongly counteractive: nutrient addition drives plant species loss through intensified competition for light, whereas herbivores prevent competitive exclusion by increasing ground-level light, particularly in productive systems. Here we use experimental data spanning a globally relevant range of conditions to test the hypothesis that herbaceous plant species losses caused by eutrophication may be offset by increased light availability due to herbivory. This experiment, replicated in 40 grasslands on 6 continents, demonstrates that nutrients and herbivores can serve as counteracting forces to control local plant diversity through light limitation, independent of site productivity, soil nitrogen, herbivore type and climate. Nutrient addition consistently reduced local diversity through light limitation, and herbivory rescued diversity at sites where it alleviated light limitation. Thus, species loss from anthropogenic eutrophication can be ameliorated in grasslands where herbivory increases ground-level light.

Practice parameter update: the care of the patient with amyotrophic lateral sclerosis: drug, nutritional, and respiratory therapies (an evidence-based review): report of the Quality Standards Subcommittee of the American Academy of Neurology.

Abstract: Objective: To systematically review evidence bearing on the management of patients with amyotrophic lateral sclerosis (ALS). Methods: The authors analyzed studies from 1998 to 2007 to update the 1999 practice parameter. Topics covered in this section include slowing disease progression, nutrition, and respiratory management for patients with ALS. Results: The authors identified 8 Class I studies, 5 Class II studies, and 43 Class III studies in ALS. Important treatments are available for patients with ALS that are underutilized. Noninvasive ventilation (NIV), percutaneous endoscopic gastrostomy (PEG), and riluzole are particularly important and have the best evidence. More studies are needed to examine the best tests of respiratory function in ALS, as well as the optimal time for starting PEG, the impact of PEG on quality of life and survival, and the effect of vitamins and supplements on ALS. Recommendations: Riluzole should be offered to slow disease progression (Level A). PEG should be considered to stabilize weight and to prolong survival in patients with ALS (Level B). NIV should be considered to treat respiratory insufficiency in order to lengthen survival (Level B), and may be considered to slow the decline of forced vital capacity (Level C) and improve quality of life (Level C). Early initiation of NIV may increase compliance (Level C), and insufflation/exsufflation may be considered to help clear secretions (Level C). Neurology ® 2009;73:1218 –1226 GLOSSARY AAN American Academy of Neurology; ALS amyotrophic lateral sclerosis; FVC forced vital capacity; HFCWO high frequency chest wall oscillation; MIE mechanical insufflation/exsufflation; MIP maximal inspiratory pressure; NIV noninvasive ventilation; PCEF peak cough expiratory flow; Pdi transdiaphragmatic pressure; PEG percutaneous endoscopic gastrostomy; QOL quality of life; RIG radiologically inserted device; SNP sniff nasal pressure; TIV tracheostomy invasive ventilation.