Freezing tolerance is one of the most important traits that determine the productivity and distribution of plants. Even in global climate changes era, there are frequent occasions in both regional and/or local environments that temperature drops quite rapidly and stays low for a few days to weeks during crop growing seasons, especially in late fall and early spring. Thus, the increase of plant freezing tolerance is critical to maintain or improve crop productivity. Temperate plants including many crop species have an ability to increase their freezing tolerance when exposed to low but non-freezing temperatures, which is known as cold acclimation (for example, a winter rye can withstand freezing as low as -30℃ after cold acclimation). Many studies have tried to elucidate mechanism(s) of cold acclimation in plants but it still remains to be cleared in many issues due to diverse and seemingly unrelated changes occurring during cold acclimation. Because the plasma membrane (PM) is the primary site of freezing injury, the maintenance and rearrangement of the PM is thought to be the key issue for cold acclimation and survival at freezing temperatures. Thus, it is reasonable to hypothesize that diverse changes occurring during cold acclimation ultimately lead to the stabilization of the PM against various stresses imposed by freezing (such as dehydration, salinity, osmotic and mechanical stresses). This has been the standpoint of our research programs that are described in this article. First, this article overviews how plant cells respond to extracellular freezing and how different freeze-induced lesions occur at the PM before and after cold acclimation. Next, evidence of dynamic alterations in the PM compositions during cold acclimation is described. In addition, a recently proposed concept of the PM organization, microdomains that consist of specific lipid and protein components, is introduced. Microdomains in the PM are likely involved in functional changes of the PM, which have significant effects on the increase in freezing tolerance in plant cells. Lastly, experimental evidence showing the functional involvement of lipids and proteins in the PM is summarized. Apparently, PM components are actively involved in the reorganization of its functions and structure and, as a result, the PM determines the tolerance against freezing-induced stresses in plants.

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Glass transition temperature (T_g) of biomaterials including pharmaceutical and food materials is a practically important factor. However, it is difficult to obtain a clear T_g because biomaterials are complex and heterogeneous system. In this paper useful techniques for the T_g determination of biomaterials were briefly reviewed. Isothermal aging and cooling-heating cycle rate can emphasize glass transition observed by differential scanning calorimetry. Thermal rheological analysis can provide additional information on the glass transition of biomaterials.

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Antifreeze proteins (AFPs), which have been discovered in organisms living in cold regions, have two main functions related to freezing. One is to inhibit ice growth at temperatures even below the equilibrium melting point, and the other is to inhibit ice nucleation initiated by ice nucleating agents. First, in this article, the effects of AFPs on ice growth and ice nucleation were reviewed. Then, the latest research trends of antifreeze synthetic polymers (AFSPs), which have the same functions as AFPs, are also reviewed. Finally, potential applications of AFSPs in the field of refrigeration and air conditioning are discussed.

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Bioaerosols are airborne particles that are biological in origin. Bioaerosols can be formed from nearly any process that involves biological materials and generates enough energy to separate small particles from the larger substance, such as wind, water, air, or mechanical movement. Plants, soil, water, and animals all serve as sources of bioaerosols, and bioaerosols are subsequently present in most places where any of these sources live. Bioaerosols have direct and indirect effects on our environment and life. One is to play as ice or cloud condensation nuclei, another is to act airborne pathogens to plant and animals including human.

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This article describes atmospheric icing, which is caused by the collision of supercooled minute water droplets in the atmosphere with overhead power conductor, aircraft, wind turbine and meteorological instrument. When it occurs, the degradation of the aerodynamic characteristics and/or the load increase due to the ice accretion may hamper their fundamental function, which results in a fatal accident or the collapse of the infrastructure in a worst case scenario. In the article, what influences icing exerts, how it has been studied and what measures for icing prevention have been considered are dealt with.

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In order to clarify the role of the vascular system for creating ice segregation, the water pathway through the stem of Keisukea japonica and the freezing front of ice segregation were investigated. Harvested stems of Keisukea japonica were used as plant samples. The water pathway was visualized with a 2.5mM fluorescein solution. After ice segregation was induced, the stem was tightly fixed on a microtome that cross sectioned the stem every 40μm. The light source with excitation filter illuminated the stem cross section. Fluorescence emission was captured by using CCD camera with fluorescent filter. Three-dimensional fluorescent image was reconstructed from the series of captured images. By observing horizontal cross sections, fluorescent illumination reached to the periphery of xylem. It means the freezing front should be the xylem surface. Pits on xylem cells, were 0.4μm of averaged short diameter. According to Ozawa (1989), ice segregation grew on the surface of a micropore membrane filter (≦0.2μm) that were placed in between supercooling water and surrounding atmosphere below 0℃. We anticipate the mechanism of ice segregation is based on the pore of the xylem pits and should be similar to the micropore membrane filter.

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Overwintering temperate plants can enhance freezing tolerance in response to low, non-freezing temperatures (cold acclimation, CA). When cold-acclimated plants are transferred to a warm temperature, they reversibly lose their freezing tolerance rather quickly (deacclimation, DA). Particularly, DA is important under oscillatory temperature conditions in early spring in the field but has not been studied in detail. Thus, the purpose of this study is to accumulate fundamental knowledge of DA to explore possibilities to reduce freezing injury occurring in the DA period. First, we verified changes of freezing tolerance in Arabidopsis thaliana during CA and DA periods: acquired freezing tolerance after 1 week of CA at 2℃ was lost after 2 days of DA. Next, we focused on proteomic changes of the plasma membrane that is considered to be the primary site for determination of freezing tolerance. Proteome analysis identified 647 CA and/or DA responsive-proteins with different patterns of alternations during CA and DA periods and these proteins were categorized into specific functional categories. With these results, we discussed the function of CA and DA responsive-proteins in detail.

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Cucumber tissues were preserved using an osmotic dehydrofreezing technique at -18 and -55℃. Two mechanical texture parameters, fracture stress related to the cell wall and initial modulus related to the cell membrane were measured using a texture analyzer after freeze-thawing. At -18℃ preservation, the fracture stress of osmotic dehydrofreezed cucumbers were in better condition than that of non-treated ones. But the initial modulus of osmotic dehydrofreezed cucumbers could not be better than that of non-treated ones. At -55℃ preservation, the facture stress of osmotic dehydrofreezed cucumbers were almost the same as that of non-treated ones. The initial modulus of osmotic dehydrofreezed cucumbers was worse than that of non-treated ones.

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The reaction kinetic model was so far proposed by the authors to simulate the cell survival curve as a function of cooling rate under the extracellular freezing in cryopreservation of cells. In this study, the similar mathematical model has been applied and developed to the cell survival curve as a function of end temperature under the slow freezing, where the slow-freezing injury was caused by extracellular freezing w/o intracellular freezing. The model constant, kinetic constant for cell damage and death was determined from inverse problem analysis on the basis of experiment of human erythrocytes to investigate the temperature dependence of the kinetic constant. The result shows that the reaction kinetic model is appropriate for the cell survival curve as a function of end temperature.

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Most temperate plants can increase their freezing tolerance during cold acclimation. To increase freezing tolerance, plants need not only low temperature but also light in general. However, it is not well known what colors of the light and photoreceptors involve in regulation of cold acclimation. Here we showed that wild type Arabidopsis thaliana plants cold-acclimated under blue light gained a greater freezing tolerance than those cold-acclimated under red light. In addition, when cold-acclimated under blue light, blue light receptor (cryptochrome) knock-out mutants (cry1cry2) exhibited lower freezing tolerance than wild type. However, there were no significant differences of total sugar contents in wild type that were cold-acclimated under red or blue light conditions. These data collectively suggested that blue light received through cryptochormes during cold acclimation is more efficient in increasing freezing tolerance than red right but the difference is not likely due to the extent of sugar accumulation.

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In this study, we analyzed soluble proteins in winter bud during endodormancy release. Endodormancy of winter buds of Salix bakko and Larix kaempferi was released clearly in early and late December, respectively. SDS-PAGE analysis showed that soluble protein composition of buds in each species hardly changed in a short period of endodormancy release. Proteome analysis using LC-MS/MS revealed compositional changes in soluble proteins in this period of endodormancy release. However, the proportion of soluble proteins whose levels were changed in this period was under 5% of all detected proteins in each species of winter buds, and the variation was small.

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