Investigation into the ability of roots of the poikilohydric plant Craterostigma plantagineum to survive dehydration stress

The ability of the root system of the poikilohydric plant Craterostigma plantagineum to survive dehydration was investigated. The data presented here reveal that the root system is capable of surviving dehydration, but shortly after rehydration the root system senesces. Two weeks after rehydration the growth of a complete new root system is initiated. During dehydration sucrose accumulates from 36 to a maximum of 111 micromol g-1 DW in the roots. It is suggested that the accumulation of sucrose protects the root system during dehydration. There are major stores of stachyose in the roots of Craterostigma (making up over 40% of the dry weight of the tissue) and during dehydration these stores are metabolized. It is suggested that these stachyose stores act as carbohydrate reserves for the synthesis of sucrose. However, over 350 micromol g-1 DW stachyose is metabolized in the roots, which is well in excess of that required for the accumulation of sucrose observed. It is likely that the stachyose reserves in the root system are translocated to other regions of the plant to support carbohydrate metabolism during dehydration of the tissue. During rehydration, the stachyose reserves return to their original level within 96 h. There is no change in the elevated sucrose content of the roots over this period. Thus the roots maintain the protective properties of sucrose much longer than they are needed. The maintenance of high sucrose contents in rehydrating roots is discussed as a possible survival strategy against recurrent desiccation events.     

Age to survive: DNA damage and aging

Aging represents the progressive functional decline and increased mortality risk common to nearly all metazoans. Recent findings experimentally link DNA damage and organismal aging: longevity-regulating genetic pathways respond to the accumulation of DNA damage and other stress conditions and conversely influence the rate of damage accumulation and its impact for cancer and aging. This novel insight has emerged from studies on human progeroid diseases and mouse models that have deficient DNA repair pathways. Here we discuss a unified concept of an evolutionarily conserved 'survival' response that shifts the organism's resources from growth to maintenance as an adaptation to stresses, such as starvation and DNA damage. This shift protects the organism from cancer and promotes healthy aging.     

The effect of extreme dehydration on photosynthetic activity of Sphagnum denticulatum cultivated genotypes from different habitats

Abstract

The effect of water deficit on drought-sensitive peat mosses’ photosynthetic activities were analyzed in Sphagnum denticulatum genotypes representing two ecotypes–aquatic and terrestrial. All plants, cultivated for a long time in common garden conditions, were desiccated to a water content of less than 2% of controls and subsequently rehydrated for up to 30?days. The aquatic control plants showed shade adaptations as expressed by the F₀, F_v/F₀ and Chl a/b ratios which may reflect the conditions at the parental habitat. The ecotype- and genotype-specific responses to desiccation and rehydration were observed. Under desiccation, the photoinhibition was greater in the terrestrial plants (as demonstrated by lower F_v/F_m and Φ_PSII), in comparison with the aquatic plants. This suggests either severe damage of photo centers or better photoprotection mechanisms. Although there were no consistent differences between ecotypes across treatments, the signs of intraspecific variation in desiccation sensitiveness, which presumably arose from plasticity and local adaptation of plants to their parental environments, were detected. Genotypes and their place of origin should be taken into account in future studies.     

Freeman Hospital: the will to survive.

The future looks uncertain for the Freeman Hospital trust in Newcastle upon Tyne. There are plans to rationalise the health service in Newcastle by shifting resources from secondary to primary care, and by providing more services locally for people who live in the region but outside Newcastle. These could reduce the level of contracts that purchasers place with the trust in the future. Staff at the trust say the service they provide is good value for money, but purchasers do not seem to take this into account. Instead of choosing from a "shopping list" of priced procedures, purchasers are forcing the trust to dovetail its prices to meet their budgets. There is also concern at the potential impact on the trust''s financial situation of reduced working hours for junior doctors and the Calman proposals on training.     

Mitochondrial dynamics: to be in good shape to survive

Mitochondria are essential organelles of all eukaryotic cells that play a key role in several physiological processes and are involved in the pathology of many diseases. These organelles form a highly dynamic network, which results from continuous fusion and fission processes. Importance of these processes is underlined by inherited human diseases caused by mutations in two mitochondrial pro-fusion genes: Charcot-Marie-Tooth disease, caused by mutations in Mitofusin 2 gene and ADOA due to mutations in OPA1. During apoptosis, the mitochondrial network is disintegrated and the outer mitochondrial membrane permeabilized, which results in the release of several apoptogenic proteins, including cytochrome c. Although modulating mitochondrial fusion and fission machineries has been reported to influence the apoptotic response to various stimuli, it is still unclear whether fission is absolutely required for apoptosis. In this review, we present the latest progress in the field of mitochondrial dynamics with a particular emphasis on its implication in apoptosis and in diseases.     

Radioresistance of Deinococcus radiodurans: functions necessary to survive ionizing radiation are also necessary to survive prolonged desiccation.

Forty-one ionizing radiation-sensitive strains of Deinococcus radiodurans were evaluated for their ability to survive 6 weeks of desiccation. All exhibited a substantial loss of viability upon rehydration compared with wild-type D. radiodurans. Examination of chromosomal DNA from desiccated cultures revealed a time-dependent increase in DNA damage, as measured by an increase in DNA double-strand breaks. The evidence presented suggests that D. radiodurans' ionizing radiation resistance is incidental, a consequence of this organism's adaptation to a common physiological stress, dehydration.     

The soybean retroelement SIRE1 uses stop codon suppression to express its envelope-like protein

The soybean SIRE1 family of Ty1/copia retrotransposons encodes an envelope-like gene (env-like). We analysed the DNA sequences of nine SIRE1 insertions and observed that the gag/pol and env-like genes are in the same reading frame and separated by a single UAG stop codon. The six nucleotides immediately downstream of the stop codon conform to a degenerate nucleotide motif, CARYYA, which is sufficient to facilitate stop codon suppression in tobacco mosaic virus. In vivo stop codon suppression assays indicate that SIRE1 sequences confer leakiness to the UAG stop codon at an efficiency of 5%. These data suggest that SIRE1 retro-elements use translational suppression to express their envelope-like protein; this is in contrast with all characterized retroviruses, which express the envelope protein from a spliced genomic messenger RNA.     

The relationship between the digestive enzymes in arctic char,Salvelinus alpinus (Salmonidae,Osteichthyes) and its ability to survive in extreme environments

Digestive enzymes of chars from seven Austrian lakes have been studied. Trypsin activity ml⁻¹ fluid is proportional to body size but inversely proportional to the amount of food in the digestive tract. The pancreas appears to secrete trypsin ± continuously and the activity measureable in the intestinal fluid seems to depend largely on the gut passage rate. There is no seasonal rhythm of enzyme activity. Amylase activity is very weak. Pepsin activity seems to depend mostly on the dilution of the gastric juice. The results indicate that the steering mechanisms of digestive enzymes in salmonidae are well distinct from other families. This work was part of a PH. D. thesis (Reimer, 1984). This work was part of a PH. D. thesis (Reimer, 1984).     

Cellular responses to extreme water loss: The water-replacement hypothesis

The previously advanced hypothesis that desiccation resistance involves the replacement of water adjacent to intracellular surfaces with polyhydroxy compounds has been supported by experiments on cysts of the brine shrimp, Artemia, and in a model system of albumin-glycerol-water, using nuclear magnetic resonance spectroscopy, microwave dielectrics, and density measurements. We have also considered other problems that cells face when large fractions of their total water content are removed. Observations by other investigators have indicated that a variety of mammalian cells can lose roughly 50% of their water and survive; for a given cell type death occurs if its volume is reduced below a certain minimum level. Membrane damage has previously been suggested to be a major cause of dehydration damage. We have proposed some additional plausible mechanisms that might also be involved.     

Degrade to survive: the intricate world of piroplasmid proteases

Piroplasmids of the genera Babesia, Theileria, and Cytauxzoon are tick-transmitted parasites with a high impact on animals and humans. They have complex life cycles in their definitive arthropod and intermediate vertebrate hosts involving numerous processes, including invasion of, and egress from, host cells, parasite growth, transformation, and migration. Like other parasitic protozoa, piroplasmids are equipped with different types of protease to fulfill many of such essential processes. Blockade of some key proteases, using inhibitors or antibodies, hinders piroplasmid growth, highlighting their potential usefulness in drug therapies and vaccine development. A better understanding of the functional significance of these enzymes will contribute to the development of improved control measures for the devastating animal and human diseases caused by these pathogens.     

How to survive in the host: the Yersinia lesson

The Yop virulon allows Yersinia spp. to resist the immune response of the host by injecting harmful proteins into host cells. It is composed of four elements: (i) type III secretion machinery called Ysc; (ii) a set of proteins required to translocate the effector proteins inside the eukaryotic cells; (iii) a control system, and (iv) six Yop effector proteins.     

The stratagem utilized by the plasminogen activator from the snake Trimeresurus stejnegeri to escape serpins

The plasminogen activator isolated from the venom of the snake Trimeresurus stejnegeri (TSV-PA) triggers plasmin production, along with tissue-type plasminogen activators (t-PA) and urokinase (u-PA). The half-life of TSV-PA in plasma is remarkable. We unveil in this paper two of the molecular mechanisms allowing TSV-PA to escape inhibition by plasma serpins. The first involves a phenylalanine at position 193 (chymotrypsinogen numbering system). Phe(193) distinguishes TSV-PA from nearly all trypsin-like proteinases, having glycine at this position. A mutant of TSV-PA (F193G), in which Phe(193) had been replaced by a glycine, was inactivated by plasminogen activator inhibitor 1 (PAI-1) and alpha(2)-antiplasmin 100-fold more rapidly than the wild-type enzyme. The second mechanism originates from the 37-loop of TSV-PA. Swapping the 37-loop of TSV-PA for either that of t-PA or that of u-PA also increased dramatically the rate of inactivation by PAI-1. Loop swapping and F193G mutations were additive, resulting in a rate of inactivation by PAI-1 that was 4 orders of magnitude higher than for the wild-type enzyme. The potential role of Phe(193) and of the 37-loop in the immunity of TSV-PA toward alpha(1)-antitrypsin and antithrombin is also discussed.     

Responses to environmental stresses in woody plants: key to survive and longevity

Environmental stresses have adverse effects on plant growth and productivity, and are predicted to become more severe and widespread in decades to come. Especially, prolonged and repeated severe stresses affecting growth and development would bring down long-lasting effects in woody plants as a result of its long-term growth period. To counteract these effects, trees have evolved specific mechanisms for acclimation and tolerance to environmental stresses. Plant growth and development are regulated by the integration of many environmental and endogenous signals including plant hormones. Acclimation of land plants to environmental stresses is controlled by molecular cascades, also involving cross-talk with other stresses and plant hormone signaling mechanisms. This review focuses on recent studies on molecular mechanisms of abiotic stress responses in woody plants, functions of plant hormones in wood formation, and the interconnection of cell wall biosynthesis and the mechanisms shown above. Understanding of these mechanisms in depth should shed light on the factors for improvement of woody plants to overcome severe environmental stress conditions.