▪ Abstract Many plants increase in freezing tolerance upon exposure to low nonfreezing temperatures, a phenomenon known as cold acclimation. In this review, recent advances in determining the nature and function of genes with roles in freezing tolerance and the mechanisms involved in low temperature gene regulation and signal transduction are described. One of the important conclusions to emerge from these studies is that cold acclimation includes the expression of certain cold-induced genes that function to stabilize membranes against freeze-induced injury. In addition, a family of Arabidopsis transcription factors, the CBF/DREB1 proteins, have been identified that control the expression of a regulon of cold-induced genes that increase plant freezing tolerance. These results along with many of the others summarized here further our understanding of the basic mechanisms that plants have evolved to survive freezing temperatures. In addition, the findings have potential practical applications as freezing te...

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PLANT COLD ACCLIMATION: Freezing Tolerance Genes and Regulatory Mechanisms

Plant cold acclimation: Freezing tolerance genes and regulatory mechanisms

Aim At a coarse scale, the treelines of the world`s mountains seem to follow a common isotherm, but the evidence for this has been indirect so far. Here we aim at underpinning this with facts. Location We present the results of a data-logging campaign at 46 treeline sites between 68degrees N and 42degrees S. Methods We measured root-zone temperatures with an hourly resolution over 1-3 years per site between 1996 and 2003. Results Disregarding taxon-, landuse- or fire-driven tree limits, high altitude climatic treelines are associated with a seasonal mean ground temperature of 6.7 degreesC (+/-0.8 SD; 2.2 K amplitude of means for different climatic zones), a surprisingly narrow range. Temperatures are higher (7-8 degreesC) in the temperate and Mediterranean zone treelines, and are lower in equatorial treelines (5-6 degreesC) and in the subarctic and boreal zone (6-7 degreesC). While air temperatures are higher than soil temperatures in warm periods, and are lower than soil temperatures in cold periods, daily means of air and soil temperature are almost the same at 6-7 degreesC, a physics driven coincidence with the global mean temperature at treeline. The length of the growing season, thermal extremes or thermal sums have no predictive value for treeline altitude on a global scale. Some Mediterranean (Fagus spp.) and temperate South Hemisphere treelines (Nothofagus spp.) and the native treeline in Hawaii (Metrosideros) are located at substantially higher isotherms and represent genus-specific boundaries rather than boundaries of the life-form tree. In seasonal climates, ground temperatures in winter (absolute minima) reflect local snow pack and seem uncritical. Main conclusions The data support the hypothesis of a common thermal threshold for forest growth at high elevation, but also reflect a moderate region and substantial taxonomic influence.

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A world-wide study of high altitude treeline temperatures

In this review I first compile data for the worldwide position of climate-driven alpine treelines. Causes for treeline formation are then discussed with a global perspective. Available evidence suggests a combination of a general thermal boundary for tree growth, with regionally variable “modulatory” forces, including the presence of certain taxa. Much of the explanatory evidence found in the literature relates to these modulatory aspects at regional scales, whereas no good explanations emerged for the more fundamental global pattern related to temperature per se, on which this review is focused. I hypothesize that the life form “tree” is limited at treeline altitudes by the potential investment, rather than production, of assimilates (growth as such, rather than photosynthesis or the carbon balance, being limited). In shoots coupled to a cold atmosphere, meristem activity is suggested to be limited for much of the time, especially at night. By reducing soil heat flux during the growing season the forest canopy negatively affects root zone temperature. The lower threshold temperature for tissue growth and development appears to be higher than 3°C and lower than 10°C, possibly in the 5.5–7.5°C range, most commonly associated with seasonal means of air temperature at treeline positions. The physiological and developmental mechanisms responsible have yet to be analyzed. Root zone temperature, though largely unknown, is likely to be most critical.

/pdf/a-re-assessment-of-high-elevation-treeline-positions-and-2h8ncswvxc.pdf

A re-assessment of high elevation treeline positions and their explanation

In a world of increasing atmospheric CO2, there is intensified interest in the ecophysiology of photosynthesis and more attention is being given to other aspects of carbon exchange and storage in natural ecosystems. For example, how much will the photosynthesis of terrestrial and aquatic vegetation change as global CO2 increases? Are there major ecosystems, such as the boreal forests, which may become important sinks of CO2 and slow down the effects of anthropogenic CO2 emissions on climate? This volume reviews the progress which has been made in understanding photosynthesis in the past few decades at several levels of integration, from the molecular level to canopy, ecosystem and global scales.

Ecophysiology of Photosynthesis

Low temperature represents, together with drought and salt stress, one of the most important environmental constraints limiting the pro ductivity and the distribution of plants on the Earth. Winter survival, in particular, is a highly complex phenomenon, with regards to both stress factors and stress responses. The danger from winter cold is the result not only of its primary effect, i. e. the formation of ice in plant tissues; additional threats are presented by the freezing of water in and on the ground and by the load and duration ofthe snow cover. In recent years, a number of books and reviews on the subject of chilling and frost resistance in plants have appeared: all of these publications, however, concentrate principally on the mechanisms of injury and resistance to freezing at the cellular or molecular level. We are convinced that analysis of the ultrastructural and biochemical alterations in the cell and particularly in the plasma membrane during freezing is the key to understanding the limits of frost resistance and the mechanisms of cold acclimation. This is undoubtedly the immediate task facing those of us engaged in resistance research. It is nevertheless our opinion that, in addition to understanding the basic physiological events, we should be careful not to overlook the importance of the comparative aspects of the freezing processes, the components of stress avoidance and tolerance and the specific levels of resistance."

Frost Survival of Plants: Responses and Adaptation to Freezing Stress

Frost survival of plants

Plant cold hardiness and freezing stress :mechanisms and crop implications , Plant cold hardiness and freezing stress :mechanisms and crop implications , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Plant cold hardiness and freezing stress :mechanisms and crop implications

I HAVE succeeded1 in keeping alive living materials from the cell interiors of which all the easily freezable water was drawn by sufficient extra-cellular freezing at −30° C., after immersion in liquid nitrogen.

Survival of the Twig of Woody Plants at −196° C.

Freezing resistance studies were carried out on Salix sachalinensis (northern Japan), S. Sieboldiana (southwestern Japan), S. babylonica (Japan proper and Hachijo Island), S. caerulea (Lahore, Pakistan), S. tetrasperma (Singapore and Quetta, Pakistan), S. bonplandiana (Mexico City), and S. safsaf (Cairo). Twigs of the tenderest willows (S. Sieboldiana) wintering in the southwestern part of Japan resisted freezing to about —15°C, but when hardened at —3°C for 14 days in Sapporo, they resisted freezing at °50°C. After growing in Sapporo (northern Japan) for 1 year, these twigs survived immersion in liquid nitrogen (—196°C) following prefreezing at —20°C in winter. Cuttings from willows native to the tropics, when grown outdoors in Sapporo for 1 year, produced twigs which resisted freezing to about —30°C for 16 hr. A genetic potential to withstand freezing to very low temperatures is apparently present even in tropical willows. The temperatures most effective in producing maximum freezing resistance were nearly the same for both northern and subtropical willows irrespective of their native habitats, and the degree of freezing resistance in winter of any species of willow differed considerably and depended on air temperature in the localities at which plants were wintering.

A. Sakai

Papers

Frost Survival of Plants: Responses and Adaptation to Freezing Stress

Frost survival of plants

Plant cold hardiness and freezing stress :mechanisms and crop implications

Survival of the Twig of Woody Plants at −196° C.

Freezing Resistance in Willows from Different Climates