Stomatal pores surrounded by a pair of guard cells regulate the gas exchange between plants and atmosphere through opening and closing their apertures in response to various environmental stimuli. Blue light induces the opening of stomata, which promotes plant growth and development through the uptake of CO_2 for photosynthesis and loss of water vapor via the transpiration. The transpiration decreases the leaf temperature by the evaporative cooling and enable plants to survive under high temperature conditions. In this review, we will focus on the mechanism of blue light-dependent stomatal opening, which facilitates leaf cooling.

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Plants respond to various environmental stimuli such as temperature shifts, by activating each component in the signaling cascade such as Ca^<2+> channels, required for adaptations to changing environments. In this study, we tested the effects of naturally existing rare earth elements (Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu) added as chloride salts, on Ca^<2+> influx in induced by two different temperature stresses, namely cold shock and heat shock, in suspension-cultured transgenic tobacco cell line (BY-2) expressing aequorin, a Ca^<2+>-sensitive luminescent protein in its cytosol. Action of Al^<3+> a putative TPC1-type channel inhibitor was also examined. Based on the results obtained, the nature of temperature-sensitive Ca^<2+> influx was discussed.

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Environmental stresses - low temperature, drought and salinity in particular - are major factors limiting the growth and production of crops. The development and improvement of stress tolerance of crops are primary targets for plant molecular and genetic breeding. Recent genetic and biochemical studies have revealed that protein phosphorylation plays an essential role in induction of stress tolerance-related genes in higher plant. Here, we focused on functions of trehalose synthesis pathway and a SNF1-related protein kinase (SnRK) of tomato under various stresses. This article briefly describes expression of trehalose metabolism-related genes and a novel stress-activated SnRK homolog, LeSRK2C, of tomato involved in low-temperature signal and chilling tolerance. Application of genetic engineering of stress-activated kinase and trehalose synthesis-related genes for breeding low-temperature tolerant tomato are discussed.

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Aquaporins are membrane proteins facilitating the membrane transport of water and low molecular weight compounds. Recent studies have indicated that aquaporins are involved in cellular tolerance mechanisms under low temperature stress in plants and insects. Critical roles of aquaporins in cold tolerance and the influence of H_2O_2 were suggested in the cucumber and figleaf gourd. Reduction of water uptake was observed in rice under chilling stress, in which the down-regulation of aquaporin expression and probable inactivation of aquaporins were involved. Glycerol and water transport by aquaporins was investigated, and revealed to be essential for freezing tolerance in insect cells.

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In order to elucidate the concentration and deposition of silicic acid in rice plant, its concentration and chemical form in xylem sap at the different four growth periods were examined by spectrophotometry. In addition, some major elements included in the soil solution around the root of rice plant and the xylem sap were determined by ion chromatography. Silicic acid was quite concentrated by the uptake of soil solution from soilsphere to xylem through the root and the silicic acid concentration was ten time higher than the solubility of amorphous silica at ordinary temperature. Surprisingly, the silicic acid did not polymerize to form polysilicic acid in the xylem but was present as monosilicic acid. Whereas the concentration of other elements were not so high, some showed the similar concentration to those in the soil solution, indicating that silicic acid is specifically concentrated by root but the polymerization in the xylem is retarded by a unknown factor. According to the observation of silica deposited on the cell wall of epidermal cells of leaves of rice plant by SEM-EDX, the shape of silica particles and their distribution were geometrically regular, suggesting that the deposition of silica in rice plant may be controlled accurately by the template reactions.

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This paper dealt with the osmotic response and subsequent injury of isolated cells in suspension resulted from concentration of extracellular NaCl solution, which plays an important role in the damage mechanism during freezing. Survival of human prostate cancer cells during and after exposure to hyperosmotic NaCl solution was measured using a perfusion microscope as a function of NaCl concentration, the time of exposure and the rate of change in concentration, to examine the mechanism of cell injury. The influence of osmotic injury on the cell damage during slow freezing of cells was also examined quantitatively by comparing the perfusion experiment with a freezing experiment.

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The effect of taurine on the survival of Saccharomyces cerevisiae after freezing and oxidative stress was investigated. In addition, proline and NaCl were used as a comparison. The accumulation of taurine in yeast cells seemed to lead to the enhancement of tolerance to freezing and oxidative stress in yeast. The stress tolerance was positively correlated with the concentrations of taurine added to the medium. Although taurine appeared to be less effective than proline in the development of freezing tolerance, based on intracellular amounts, taurine protected cells more effectively than proline. Our results suggest that taurine, as well as proline, may function as a cryoprotectant and/or an antioxidant in yeast.

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Trpm5, calcium-activated cation channel of the TRP superfamily, is highly expressed in taste buds of the tongue, where it has a key role in the perception of sweet, umami and bitter tastes. Activation of Trpm5 occurs downstream of the activation of G-protein-coupled taste receptors and is proposed to generate a depolarizing potential in the taste receptor cells. Factors that modulate Trpm5 activity are therefore expected to influence taste. Here we show that Trpm5 is a highly temperature-sensitive, heat-activated channel: inward Trpm5 currents increase steeply at temperatures between 15 and 35 degrees C. Heat activation is due to a temperature-dependent shift of the activation curve, in analogy to other thermosensitive TRP channels. Moreover, we show that increasing temperature between 15 and 35 degrees C markedly enhances the gustatory nerve response to sweet compounds in wild-type but not in Trpm5 knockout mice. The strong temperature sensitivity of Trpm5 may underlie known effects of temperature on perceived taste in humans, including enhanced sweetness perception at high temperatures and 'thermal taste`, the phenomenon whereby heating or cooling of the tongue evoke sensations of taste in the absence of tastants.

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Hibernation is characterized by the profound decrease in body temperature and metabolism, which is thought to save energy expenditure during periods of severe climate and food shortage. The Syrian hamster (Mesocricetus auratus) is known as a facultative hibernator, unlike the ground squirrel, a seasonal hibernator. We have established the system by which the hamsters can be introduced into hibernation for the investigation throughout the year. When the hamsters are kept under the conditions of cold (5±1℃) and short photoperiod (2hr light/22 hr dark), about 80% of animals go into the state of hibernation after 7 to 20 weeks. The mean hibernation-starting period is about 15 weeks. The torpor, a quiescent state with low body temperature, of the hamsters lasts usually 2 to 5 days, and the torpor bouts are interrupted by periodic arousals. The hamsters experience repeated cycles of torpor and arousal throughout the hibernation period (ca. 2 months). This phenomenon would lead to elevation of reactive oxygen species (ROS) generation, but no apparent damages have been detected in the hamsters. To study the blood antioxidant status during arousal from hibernation in the Syrian hamster, we determined the levels of antioxidative enzymes in the blood. Superoxide dismutase (SOD) and catalase (CAT) activities increased transiently in blood during arousal. These results suggest that both SOD and CAT may play some roles in the antioxidative defense mechanism of hibernating hamsters. We have expected that the study of hibernation would be useful for the therapy for brain/heart diseases, organ transplantation and space travel etc. in the future.

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