Anoxic Shock Research Articles

Molecular Mechanisms in Understanding Anoxia Tolerance in Rice Seeds under Submergence and Their Implication in Rice Biotechnology

Submergence in rice fields creating inundation stress and realizing anoxia or hypoxia is a problem in agriculture. Seeds under this oxygen deficit are faced with fermentative respiration, where the end product would be poisoning the tissue viability. This is more aggravated in direct seeded rice cultivation with the accumulation of lactate as a poison. This review is concerned with the basic insights into anoxia tolerance in seeds and possible strategies to reduce anoxic shock through the modification of metabolism preceded by gene expression. The major concern of anoxic germination is starch metabolism and downstream physiological realization to facilitate escape or quiescence strategy, overcoming submergence stress. The coleoptiles facing hypoxic stress mated with transcripts for oxidative traits, energy metabolism, and proteins for membrane peroxidation in support of energy metabolism are the most important. Hypoxic genes are recovered from traditional indica and japonica land races of rice, and show changes in glycolytic flux and sugar sensing. Anoxic germination and seedling vigor are based on a combinational regulation of oxidative stress and fermentative catabolism. De novo antioxidant and antioxidative enzyme production can support improved seed germination in this condition. Pre-harvest spouting with seed-coat-induced dormancy, hormonal ratios, and hydrolyses would be of concern. Therefore, comprehensive analysis aimed to understand rice seed priming for better gas exchange, diffusion, temperature sensitivity, ion uptake, redox balance, and others. Still, in-depth insights are being awaited for better understanding the physiological and molecular basis using a multi-omics approach for better seed priming to overcome the anoxic/hypoxic revelation mostly acquainted with submergence stress.

ROS Production and Scavenging under Anoxia and Re-Oxygenation in Arabidopsis Cells: A Balance between Redox Signaling and Impairment.

Plants can frequently experience low oxygen concentrations due to environmental factors such as flooding or waterlogging. It has been reported that both anoxia and the transition from anoxia to re-oxygenation determine a strong imbalance in the cellular redox state involving the production of reactive oxygen species (ROS) and nitric oxide (NO). Plant cell cultures can be a suitable system to study the response to oxygen deprivation stress since a close control of physicochemical parameters is available when using bioreactors. For this purpose, Arabidopsis cell suspension cultures grown in a stirred bioreactor were subjected to a severe anoxic stress and analyzed during anoxia and re-oxygenation for alteration in ROS and NO as well as in antioxidant enzymes and metabolites. The results obtained by confocal microscopy showed the dramatic increase of ROS, H2O2, and NO during the anoxic shock. All the ascorbate-glutathione related parameters were altered during anoxia but restored during re-oxygenation. Anoxia also induced a slight but significant increase of α-tocopherol levels measured at the end of the treatment. Overall, the evaluation of cell defenses during anoxia and re-oxygenation in Arabidopsis cell cultures revealed that the immediate response involving the overproduction of reactive species activated the antioxidant machinery including ascorbate-glutathione system, α-tocopherol and the ROS-scavenging enzymes ascorbate peroxidase, catalase, and peroxidase making cells able to counteract the stress toward cell survival.

Cultivation of Arabidopsis cell cultures in a stirred bioreactor at variable oxygen levels: Influence on tocopherol production

In plants, an increased production of toxic oxygen species is commonly observed under low oxygen stress, but cellular responses still have to be fully investigated. Plant cell cultures can be a valuable tool to study plant metabolic responses to various environmental stresses including low oxygen condition. Arabidopsis suspension cultures growing in shake flasks were subjected to hypoxia by stopping shaking for different intervals, showing an increase of the antioxidant metabolite α‐tocopherol. In order to obtain a more controlled condition, cultivation of Arabidopsis suspension cultures was established in a 5‐l stirred bioreactor. A constant aeration of 20% dissolved oxygen was found to be the most suitable for cell growth. A 4‐h anoxic shock was induced by suspending the aeration and flushing into the vessel with nitrogen. During the anoxic stress, tocopherol levels resulted increased at the end of the treatment, indicating that the complete oxygen deprivation, indeed, induced a defence response involving antioxidant metabolism. The presence of an oxidative stress as a consequence of anoxic condition was also confirmed by the increased levels of H2O2. Overall, these results indicate that Arabidopsis suspension cultures grown in a stirred bioreactor can be a useful in vitro system for investigating low oxygen stress.

Increased hexose transport in the roots of tomato plants submitted to prolonged hypoxia

We investigated the effects of prolonged hypoxia on the sugar uptake in tomato (Solanum lycopersicum L. var. MP-1) roots. Hydroponic cultures of whole tomato plants were submitted to hypoxic treatment for 1 week, and the roots were analyzed for sugar concentrations, hexose uptake and hexose transporter expression level. Contrary to what has been observed after anoxic shock or short-term hypoxic treatment, we show that sugar concentrations increase and hexose uptake is up-regulated in the roots after 1 week of hypoxic treatment. Increased hexose transport is concomitant with the induction of the hexose transporter gene LeHT2. These responses may be due either to a direct effect of low O(2) supply, or to a secondary effect associated with the increase in sugar concentrations, which, typically, develops in most hypoxic plants.

Hypoxia Induces Anoxia Tolerance in completely Submerged Rice Seedlings

Summary Survival of four rice (Oryza sativa L.) cultivars was evaluated after submergence in water containing different oxygen concentrations. The presence of O2 in the floodwater was critical for the survival of 14-day-old seedlings: there was no effect of 4 d submergence in air-saturated water (0.24 mol· m-3 · O2), or floodwater containing O2 concentrations down to 0.05 mol · m-3, whereas when seedlings were exposed to an «anoxic shock» (0.00 mol · m-3 · O2), death of all four cultivars occured within 24–42 h. Prior exposure of seedlings to a hypoxic pre-treatment (submergence with 0.05 mol · m-3 · O2 for 24 h) greatly improved the tolerance to 24 h anoxia in all four cultivars. Two submergence tolerant cultivars (IR49830 and FR13A) showed much greater tolerance to anoxia than two intolerant cultivars (IR36 and IR42). Following the hypoxic pre-treatment, only the two tolerant cultivars could tolerate 42 h anoxia, and IR49830 seedlings could withstand up to 3d of submergence in anoxia. The two enzymes of ethanolic fermentation alcohol dehydrogenase (ADH, EC 1.1.1.1) and pyruvate decarboxylase (PDC, EC 4.1.1.1) were induced by the hypoxic pre-treatment. The activity of ADH was correlated to cultivar differences in anoxia tolerance. However, this enzyme is unlikely to limit the rate of ethanol fermentation since its in vitro activity was two orders of magnitude greater than the observed ethanolic fermentation rates. The in vitro activity of PDC was an order of magnitude lower than that of ADH, and showed a clear correlation with ethanol fermentation rates but was not correlated with anoxia tolerance. Our results suggest that the complete absence of oxygen in floodwater will have a major adverse effect on rice plants during submergence, and that the rice plant’s ability to adapt to anoxic conditions is an important component of submergence tolerance. These findings are discussed in relation to metabolic adaptations to alleviate the adverse effects of anoxia during submergence.

RESPONSE OF EUCALYPTUS MARGINATA (JARRAH) TO SIMULATED WATERLOGGING AND PHYTOPHTHORA CINNAMOMI INFECTION

This study examined the effect of simulated temporary waterlogging the interaction between E. marginata and P. cinnamomi. An aeroponic chamber has been designed which allows the roots of 7 month old clonal plants or seedlings to be subjected to a range of oxygen concentrations. Roots grown under normal oxygen were compared with those that had been exposed to either 6 days of hypoxia (2 mg O2 l-1) or 6 hr. of anoxia (< 0.05 mg O2 l-1) prior to infection by zoospores of P. cinnamomi. The roots were inoculated with a 5 μl suspension of zoospores and harvested after 2 days. Pre-treatment with an anoxic shock resulted in more rapid lesion extension, and an hypoxic treatment of 6 days in less rapid lesion extension, than seen in clones grown under normal oxygen conditions. The reduced susceptibility of hypoxic treated roots and the increased susceptibility of anoxic treated roots could not be explained by either defense enzyme accumulation or soluble carbohydrate accumulation. Studies are now focusing on other changes in metabolism associated with hypoxia that may explain these differences.

The Syndrome of Hystero-Encephalopathy in Military Psychiatric Casualties

In a previous communication to this Journal, the author described the results of three years' experience of pharmaco-electrical shock-therapy in the schizophrenic and depressive psychoses, and presented clinical and experimental evidence for an organic basis of these conditions. It was shown, firstly, that there is convincing evidence for supposing that deranged oxygen-glucose metabolism of the cerebral neurones is the essential lesion; and, secondly, that all these conditions can be classified according to their response to shock-therapy into two groups—dysoxic encephalopathy, or cerebral dysoxia, in which oxygen-metabolism is principally at fault, and which responds to anoxic shock; and dysglycolytic encephalopathy, or cerebral dysglycia, in which glucose-metabolism is at fault, and which responds to hypoglycaemic shock. The former condition is synonymous with depressive states, and the latter with schizophrenic reaction-types in the orthodox terminology.

ADVANTAGES AND DANGER OF COMBINED ANOXIC AND INSULIN SHOCK

The effect of short periods of simple anoxia uncomplicated by the accumulation of carbon dioxide or by anesthetics has been studied in experiments on progressive thrombosis since the beginning of 1937. The experimental procedure employed was briefly denoted as anoxic shock. Steadily flowing oxygen-nitrogen mixtures in which the oxygen was gradually reduced produced a slowly but progressively increasing anoxia, which caused, within fifteen to thirty minutes, a state of gasping respiration or the arrest of respiration. The symptoms elicited were so much like those described by observers of Sakel's1insulin shock that in his detailed report on insulin shock, given at the staff meeting of the Memorial Hospital, Albany, N. Y., on Nov. 23, 1937, Dr. W. B. Cornell seemed to describe all the symptoms I had observed in rabbits during anoxic shock. I was so impressed that in the discussion which followed I dared to say that I

Comparative Experimental Studies on Symptomatology and Anatomical Changes Produced by Anoxic and Insulin Shock

Thirty-eight rabbits were exposed to anoxia for short periods during which the oxygen percentage in the mixture with nitrogen was so slowly decreased as to avoid excitement, though in some instances the anoxia was prolonged until respiration ceased. This slow deprivation of oxygen is termed anoxic shock. The rabbits were exposed to from 1 to 51 anoxic shocks during a period of from 1 to 60 days. The duration of a single shock varied from 15 to 60 minutes. Twenty-nine other rabbits were injected with insulin sufficient to produce coma and convulsions.The symptoms of the insulin and anoxic shock were similar except that those due to anoxia occurred on a more rapid time scale. Anoxia was characterized by increase of the respiratory rate, dilatation of the ear arteries, muscular weakness, somnolence and finally decrease of the respiratory rate and complete cessation of respiration, though the heart continued beating. In insulin shock muscular weakness and somnolence also occurred before convulsions and coma. ...