When fresh vegetable tissues are subjected by freeze-thaw treatment, the texture dramatically changes softening. However, the mechanism has been still ambiguous. In this study, the restricted diffusion of water molecules in the onion tissues before and after freezing was measured using NMR (Nuclear magnetic resonance) technique. Further, the onion tissues were subjected by chloroform treatment to destroy cell membrane. From the NMR data and the cell size information observed by optical microscopic method, the water permeability inter cells for the fresh, freeze-thawed, and chloroform treatment tissues samples were calculated and compared. The results showed that the water permeability for fresh onion tissue is significantly lower, but the permeability for freeze-thawed and chloroform samples become higher considerably. On the other hand, the microscopic observation result did not show any damage in their tissue structures. From these results, it is suggested that texture changes for onion tissue after, freeze-thawing would be caused by increasing in the cell membrane permeability of water, rather than in the cell wall.

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The good relationship between ice nucleation temperature and pure water volume (radius) was reported by many researchers from the droplet experiment. In this study, many different volumes of distilled water and several aqueous solutions (1 molkg^<-1> ethylene glycol, sucrose, and polyethylene glycol Mw 200 (PEG200), and l0%wt PEG10000 solutions) were subjected for the measurement of the ice nucleation temperature and the enthalpy of ice melting by using differential scanning calorimetry (DSC). Our obtained results showed the good relationship between the ice nucleation temperature and the enthalpy of ice melting for sample solutions.

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Knowledge of dynamic state of water and membrane permeability will provide a measure against water loss of leafy vegetables. Therefore, the proton NMR relaxation time T_1 and the osmotic water permeability L_p of spinach cell membrane were measured. T_1 of water in spinach leaf was composed of long and short components. The increase in long T_1 suggested the deterioration of cell membrane during storage. This corresponded to the increase in L_p that regulates the water movement across membrane. This finding implies that water changes its site from vacuole to cytoplasm as L_p increases and it can be detected through long T_1.

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Trehalose is known to act as a protectant against various environmental stresses, including drying, freeze, oxidation, ethanol, osmolarity and so on. In this mini review, we discuss such cross protection effect of trehalose together with possible molecular mechanisms. First, the cross protection effect against salt, freeze-dying and ethanol stresses in yeast cells are discussed based on the so-called water replacement mechanism. Second, the desiccation tolerance in larvae of Polypedilum vanderplanki is discussed based on the vitrification mechanism. Third, the antioxidant function of trehalose is discussed based on the interaction model between trehalose and a hydrophobic group, especially cis type C=C bond. Finally, it is suggested that the physicochemical origin of the cross protective function of trehalose is ascribed to the structural peculiarity of this sugar, that is, the presence of α, α-l,1 glycosidic bond.

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Polyglutamine diseases, such as Huntington disease (HD) and spinocerebellar ataxia 1 and 3, are autosomal dominant neurodegenerative disorders. They are caused by CAG trinucleotide repeat expansions that are translated into abnormally long polyglutamine tracts. One of the pathological hallmarks in polyglutamine diseases is the formation of intranuclear inclusions of polyglutamine-containing proteins in the brain. We developed a novel in vitro model system for polyglutamine diseases using myoglobin as a host protein. We searched for small molecules that inhibit polyglutamine-mediated aggregation by in vitro screening with a mutant myoglobin containing a 35 polyglutamine repeat. The screening assay revealed that disaccharides have a potential to inhibit polyglutamine-induced protein aggregation and to increase survival in a cellular model of HD. Oral administration of trehalose, the most effective disaccharide in vitro, decreased polyglutamine aggregates in the cerebrum and liver, improved motor dysfunction and extended life span in a transgenic mouse model of HD. In vitro experiments suggest that the beneficial effects of trehalose result from its ability to bind and stabilize polyglutamine-containing proteins. The lack of toxicity and high solubility, coupled with its efficacy upon oral administration, make trehalose promising as a therapeutic drug or lead compound for the treatment of polyglutamine diseases.

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Mutational analyses were performed to elucidate the stress-resistant mechanisms of extremozymes from some extremophiles, such as thermophile, alkaliphile and halophile. Probable amino acid residues that could contribute to thermostability alkaliphily and halophily of the extremozymes were clarified.

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Food-borne pathogenic and spoilage bacteria can be killed by various methods in sterilization and pasteurization processes. In the process for minimizing the reduction in food quality, after the processing, bacterial cells often do not die but are in an injured state. During the post-treatment period these injured cells carry out the stress response and repair. Probably due to these functions, they become highly resistant to the subsequent secondary stress of not only the same type (acquired tolerance), but also other types (cross protection). I stress here a possibility of serious problems derived from the occurrence of these phenomena in practical use of a consecutive process consisting of two or more different methods for inactivation of bacterial cells. The clarification of the mechanisms of the acquired tolerance and cross protection at cellular and molecular levels is expected.

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Glycinebetaine (betaine) is a compatible solute that allows plants to tolerate various kinds of environmental stress, such as cold, freezing and high salt. To examine a direct relationship between the synthesis of betaine and the stress tolerance in plants, we transformed plants, such as Arabidopsis thaliana, Oriza sativa (rice) and Lycopersicon esculentum (tomato), are unable to synthesize betaine, with the codA gene for choline oxidase from a soil bacterium that catalyzes the synthesis of betaine from choline. We observed that resultant transgenic plants obtained the ability to synthesize betaine at a concentration no higher than 1 mM and to tolerate various kinds of stress. These findings indicate that betaine effectively enhances the ability of crossprotection against environmental stress but is ineffective in osmotic regulation.

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Rice seedlings, when kept at 42 ℃ for 24 h before being kept at 5 ℃ for 7 d, did not develop chilling injury. Chilling resistance was enhanced in parallel with the period of heat-treatment. The level of APX activity was higher in seedlings exposed to 42 ℃. The levels of apxa mRNA increased within 1 h after seedlings were exposed to 42 ℃. Elevated apxa mRNA levels could also be detected after 6, 9, 12 and 24 h of heat stress. The promoter of apxa had a minimal heat shock factor (HSF) binding motif, 5'-nGAAnnTTCn-3', located 81-bp upstream to the TATA box. Heat shock induction of apxa could be possible cause of reduced chilling injury in rice seedlings. Transgenic rice plants were generated via Agrobacterium tumefaciens-mediated transformation. The level of APX activity was higher in high-expression transgenic lines than the low-expression transgenic line and non-transformed control plants. Relative to the low-expression line and non-transformed control plants, high-expression lines showed significantly less injury from the chilling stress.

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DNA microarray was applied for the evaluation of induced genes after stress conditions. Forty six kinds of stress were selected under the consideration that the stress do cause biological alteration such as growth inhibition. The induced genes were selected as the genes that pass student t-test with the p-values less than 0.050 and induced more than 2.0 times. The high frequently induced genes were HSP12, MET17, ECM4, and YGR043c. The induced genes were functionally categorized into groups of 'Metabolisms', 'Energy' and 'Stress related genes'. The well-known stress related genes such as HSPs, PDRs and glutathione related genes were also significantly induced.

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Tardigrades are hydrophilous invertebrates with four pairs of lobopodous legs forming a phylum and inhabit various environments throughout the world. Terrestrial tardigrades lose their body water almost completely and contract their body into a form called as "tun" when the surrounding water disappears. Although the dried tardigrades show no sign of life, they will recover their activity if a drop of water is given. This ametabolic dry state is called "anhydrobiosis". Anhydrobiotic tardigrades are known to tolerate a variety of extreme environments: they can survive a wide range of temperatures from -273℃ to 151℃, vacuum, hydrostatic pressure up to 600 MPa, ionizing radiation (X-rays, y-rays and ultraviolet rays) and chemicals (alcohol and methyl bromide). Tardigrades may provide a useful model system to study extreme environmental biology in the future, although the mechanisms of tolerance to extreme environments remain unknown. We will summarize extraordinary high stress tolerance in tardigrades and discuss the possible mechanism responsible for it.

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