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Animals vary tremendously in their capacities to survive anoxia, and the mechanisms responsible are poorly understood. Adult Drosophila melanogaster are rapidly paralyzed and survive up to 12 h of anoxia, whereas larvae vigorously attempt escape but then die if anoxia exceeds 2 h. Here we use nuclear magnetic resonance methods to compare the metabolome of larvae and adult D. melanogaster under normoxic conditions and after various anoxic durations up to 1 h. Glucose increased during anoxia in both larvae and adults, so anoxic death by carbohydrate limitation is unlikely for either stage. Lactate and alanine were the primary anaerobic end products in both adults and larvae. During the first 30 min of anoxia, larvae accumulated anaerobic end products (predominately lactate) at a higher rate, suggesting that larvae may experience greater initial acid-base disruption during anoxic exposures. Adult Drosophila did not possess higher levels of putative protective metabolites; however, these increased during anoxia in adults and decreased in larvae. Metabolites that decreased during anoxia in larvae included mannitol, xylitol, glycerol, betaine, serine, and tyrosine, perhaps due to use as fuels, antioxidants, or binding to denatured proteins. Adults showed significant increases in glycine, taurine, and the polyols glycerol, mannitol, and xylitol, suggesting that adults upregulate protective metabolites to prevent damage. Our results suggest that lower initial metabolic demand due to paralytic hypometabolism and capacities to upregulate protective metabolites may assist the better anoxia tolerance of adult Drosophila. [ABSTRACT FROM AUTHOR]

The article presents community recommendations on terminology and procedures used in flooding and low oxygen stress research. This include flooding, anaerobiosis, anaerobic metabolism, anoxia, hypoxia, hyperoxia/superoxia, stress conditions and scoring survival. It also discusses the challenge of monitoring oxygen levels in plants.

Seagrasses grow submerged in aerated seawater but often in low O2 sediments. Elevated temperatures and low O2 are stress factors., Internal aeration was measured in two tropical seagrasses, Thalassia hemprichii and Enhalus acoroides, growing with extreme tides and diel temperature amplitudes. Temperature effects on net photosynthesis ( PN) and dark respiration ( RD) of leaves were evaluated., Daytime low tide was characterized by high pO2 (54 kPa), pH (8.8) and temperature (38°C) in shallow pools. As PN was maximum at 33°C (9.1 and 7.2 μmol O2 m−2 s−1 in T. hemprichii and E. acoroides, respectively), the high temperatures and reduced CO2 would have diminished PN, whereas RD increased (Q10 of 2.0-2.7) above that at 33°C (0.45 and 0.33 μmol O2 m−2 s−1, respectively). During night-time low tides, O2 declined resulting in shoot base anoxia in both species, but incoming water containing c. 20 kPa O2 relieved the anoxia. Shoots exposed to 40°C for 4 h showed recovery of PN and RD, whereas 45°C resulted in leaf damage., These seagrasses are 'living near the edge', tolerant of current diel O2 and temperature extremes, but if temperatures rise both species may be threatened in this habitat. [ABSTRACT FROM AUTHOR]

• Pondweed (Potamogeton distinctus) turions can elongate in the absence of O2. Alcoholic fermentation serves to produce energy for anoxic elongation via the breakdown of starch stored in cells. However, the mechanism of cell growth during anoxic elongation is not fully understood. • Changes in pH, H+ equivalent and lactate content of the incubation medium were measured during anoxic elongation. The effects of fusicoccin (FC), indole-3- acetic acid (IAA), vanadate, erythrosine B and K+ channel blockers on anoxic elongation were examined. Cytoplasmic pH and vacuolar pH were measured by 31P nuclear magnetic resonance (NMR) spectroscopy. • Acidification of the incubation medium occurred during anoxic elongation. The contribution of CO2 and lactic acid was not sufficient to explain the acidification. FC and IAA enhanced the elongation of stem segments. Vanadate and erythrosine B inhibited anoxic elongation. Acid growth of notched segments was observed. The activity of plasma membrane H+-ATPase extracted from pondweed turions was increased slightly in anoxic conditions, but that from pea epicotyls sensitive to anoxic conditions was decreased by incubation in anoxic conditions. Both the cytoplasmic pH and vacuolar pH of pondweed turion cells chased by 32P NMR spectroscopy were stabilized during a short period < 3 h after anoxic conditions.• We propose that the enhancement of H+ extrusion by anoxic conditions induces acidification in the apoplast and may contribute to the stabilization of pH in the cytoplasm. [ABSTRACT FROM AUTHOR]

In this article the authors discuss several studies related to plants and flooding stress, which are published in the 2011 issue of the journal "New Phytologist." They say that flooding is a compound stress consists of changes inside the plant cells caused by the flood water surrounding the plant. They cite the study of D. Vashisht and colleagues on natural variation in flooding tolerance of Arabidopsis thaliana. They also mention a study on acclimation and genetic diversity in flooding.

The annual killifish Ausirofundulus limnaeus survives in ephemeral pond habitats by producing drought-tolerant diapausing embryos. These embryos probably experience oxygen deprivation as part of their normal developmental environment. We assessed the anoxia tolerance of A. limnaeus embryos across the duration of embryonic development. Embryos develop a substantial tolerance to anoxia during early development, which peaks during diapause II. This extreme tolerance of anoxia is retained during the first 4 days of post-diapause II development and is then lost. Metabolism during anoxia appears to be supported mainly by production of lactate, with alanine and succinate production contributing to a lesser degree. Anoxic embryos also accumulate large quantities of γ-arninobutyrate (GABA), a potential protector of neural function. It appears that the suite of characters associated with normal development and entry into diapause II in this species prepares the embryos for long-term survival in anoxia even while the embryos are exposed to aerobic conditions. This is the first report of such extreme anoxia tolerance in a vertebrate embryo, and introduces a new model for the study of anoxia tolerance in vertebrates. [ABSTRACT FROM AUTHOR]

Glutathione S-transferases (GSTs) play critical roles in detoxification, response to oxidative stress, regeneration of S-thiolated proteins, and catalysis of reactions in nondetoxification metabolic pathways. Liver GSTs were purified from the anoxia-tolerant turtle, Trachemys scripta elegans. Purification separated a homodimeric (subunit relative molecular mass =34 kDa) and a heterodimeric (subunit relative molecular mass = 32.6 and 36.8 kDa) form of GST. The enzymes were purified 23–69-fold and 156–174-fold for homodimeric and heterodimeric GSTs, respectively. Kinetic data gathered using a variety of substrates and inhibitors suggested that both homodimeric and heterodimeric GSTs were of the α class although they showed significant differences in substrate affinities and responses to inhibitors. For example, homodimeric GST showed activity with known α class substrates, cumene hydroperoxide and p-nitrobenzylchloride, whereas heterodimeric GST showed no activity with cumene hydroperoxide. The specific activity of liver GSTs with chlorodinitrobenzene (CDNB) as the substrate was reduced by 2.6- and 8.7-fold for homodimeric and heterodimeric GSTs isolated from liver of anoxic turtles as compared with aerobic controls, suggesting an anoxia-responsive stable modification of the protein that may alter its function during natural anaerobiosis. [ABSTRACT FROM AUTHOR]

Although grape berries have been classified as non-climacteric fruits, ongoing studies on grape ethylene signalling challenge the role of ethylene in their ripening. One of the significant molecular changes in berries is the up-regulation of ADH (alcohol dehydrogenase, EC 1.1.1.1) enzyme activity at the inception of fruit ripening and of VvADH2 transcript levels. This paper shows that the ethylene signal transduction pathway could be involved in the control of VvADH2 expression in grapevine berries and in cell suspensions. The induction of VvADH2 transcription, either in berries at the inception of ripening or in cell suspensions, was found to be partly inhibited by 1-methylcyclopropene (1-MCP), an inhibitor of ethylene receptors. Treatment of cell suspensions with 2-chloroethylphosphonic acid (2-CEPA), an ethylene-releasing compound, also resulted in a significant increase in ADH activity and VvADH2 transcription under anaerobiosis, showing that concomitant ethylene and anaerobic treatments in cell suspensions could result in changes in VvADH2 expression. All these results associated with the presence in the VvADH2 promoter of regulatory elements for ethylene and anaerobic response, suggest that the ethylene transduction pathway and anaerobic stress could be, in part, involved in the regulation of VvADH2 expression in ripening berries and cell suspensions. These data open new aspects of the expression control of a ripening-related gene in a non-climacteric fruit. [ABSTRACT FROM PUBLISHER]

Production of α-amylase during the germination of rice grains is thought to play an important role for tolerance to anoxia of these cereal grains. Under aerobic conditions α-amylases production is enhanced in response to gibberellins produced by the embryos, but the role of these hormones is less clear under anoxia. In this paper we analysed α-amylase gene expression in a rice mutant (Tan-ginbozu) severely impaired in gibberellin biosynthesis. Expression of α-amylase genes others than the gibberellin-induced Amy1A gene is observed. The expression of the Amy3D gene, which does dot require gibberellins to be induced, is high under anoxia in the Tan-ginbozu mutant suggesting that germination under anoxia can proceed thanks to the activity of the α-amylase isoform encoded by the Amy3D gene. Amy3D gene expression is repressed in the presence of high levels of soluble carbohydrates, indicating that the anaerobic expression of this gene can be triggered by a lower carbohydrate content of rice grains kept under anoxia. Germination under anoxia of Tan-ginbozu grains can proceed even in absence of exogenously-added gibberellic acid. Overall, results indicate that gibberellins are not required for the anaerobic germination of rice grains. [ABSTRACT FROM AUTHOR]

Shoot elongation of arrowhead (Sagittaria pygmaea Miq.) tubers was stimulated in anaerobic conditions. The anaerobic elongation was attributed to stimulation of cell elongation in the middle of the shoots. The anaerobic elongation of the shoots was severely inhibited by ethylene glycol bis(β-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA). The EGTA inhibition was completely nullified by exogenous CaCl2, which acts as an enhancer of anaerobic elongation. Moreover, calcium channel blockers, varapamil, diltiazem and LaCl3, inhibited the anaerobic elongation enhanced by CaCl2. These results showed that calcium plays an important role in stimulating the elongation in anaerobic conditions. Incorporation of 45Ca into the shoot tissues was measured to determine the involvement of calcium uptake in anaerobic elongation. Incorporation of 45Ca into the cell sap, which was collected from frozen and thawed shoots after thorough washing with LaCl3, was significantly stimulated in anaerobic conditions. Verapamil and diltiazem prevented the stimulation of 45Ca incorporation in anaerobic conditions. These results suggest that calcium uptake from the medium serves to enhance shoot elongation of arrowhead tubers under anaerobic conditions. [ABSTRACT FROM AUTHOR]

Oxygen plays a crucial role in energetic metabolism of most eukaryotes. Yet adaptations to low-oxygen concentrations leading to anaerobiosis have independently arisen in many eukaryotic lineages, resulting in a broad spectrum of reduced and modified mitochondrion-related organelles (MROs). In this study, we present the discovery of two new class-level lineages of free-living marine anaerobic ciliates, Muranotrichea, cl. nov. and Parablepharismea, cl. nov., that, together with the class Armophorea, form a major clade of obligate anaerobes (APM ciliates) within the Spirotrichea, Armophorea, and Litostomatea (SAL) group. To deepen our understanding of the evolution of anaerobiosis in ciliates, we predicted the mitochondrial metabolism of cultured representatives from all three classes in the APM clade by using transcriptomic and metagenomic data and performed phylogenomic analyses to assess their evolutionary relationships. The predicted mitochondrial metabolism of representatives from the APM ciliates reveals functional adaptations of metabolic pathways that were present in their last common ancestor and likely led to the successful colonization and diversification of the group in various anoxic environments. Furthermore, we discuss the possible relationship of Parablepharismea to the uncultured deep-sea class Cariacotrichea on the basis of single-gene analyses. Like most anaerobic ciliates, all studied species of the APM clade host symbionts, which we propose to be a significant accelerating factor in the transitions to an obligately anaerobic lifestyle. Our results provide an insight into the evolutionary mechanisms of early transitions to anaerobiosis and shed light on fine-scale adaptations in MROs over a relatively short evolutionary time frame. • Discovery and cultivation of two new classes of marine ciliates thriving in anoxia • Phylogenomics reveals a major clade of obligate anaerobes in ciliates • Novel insights into evolution of mitochondrial metabolism in anaerobic eukaryotes • Transitions to obligate anaerobiosis might be facilitated by prokaryotic symbionts Numerous eukaryotes have switched to anaerobiosis, variously reducing their mitochondrial metabolism. Rotterová et al. describe two new classes of obligately anaerobic ciliates with prokaryotic symbionts and reduced mitochondria with unique pathways for energetic metabolism, introducing possible mechanisms of transitions to obligate anaerobiosis. [ABSTRACT FROM AUTHOR]