Gulzar S.Sanghera et al./ Elixir Agriculture 39 (2011) 5065-5075 5065 Introduction Abiotic stresses adversely affect growth, productivity and trigger a series of morphological, physiological, biochemical and molecular changes in plants. Cold stress is a major environmental factor that limits the agricultural productivity of plants in hilly areas. Low temperature has a huge impact on the survival and geographical distribution of plants. It often affects plant growth and crop productivity, which causes significant crop losses (Xin and Browse, 2000). Plants differ in their tolerance to chilling (0-15ºC) and freezing (< 0ºC) temperatures. Plants from temperate regions are chilling tolerant, although most are not very tolerant to freezing but can increase their freezing tolerance by being exposed to chilling, non freezing temperatures, a process known as cold acclimation (Levitt, 1980), which is associated with biochemical and physiological changes (Shinozaki and Yamaguchi-Shinozaki, 1996; Thomashow, 1998; Gilmour et al. 2000). By contrast, plants of tropical and subtropical origins, including many crops such as rice, maize and tomato etc. are sensitive to chilling stress and largely lack the capacity for cold acclimation. Freezing temperature greatly limits the geographical distribution of cultivated plants and often causes severe losses in agriculture production and productivity. Conventional breeding methods have met with limited success in improving the cold tolerance of important crop plants involving inter-specific or inter-generic hybridization. Besides, in vitro induced variations have also been applied to improve the abiotic stress tolerance of various crop plants but without much success. The conventional breeding approaches are limited by the complexity of stress tolerance traits, low genetic variance of yield components under stress condition and lack of efficient selection criteria. It is important, therefore, to look for alternative strategies to develop cold stress tolerant crops Biotechnology offers new strategies that can be used to develop transgenic crop plants with improved tolerance to cold stress. A number of genes have been isolated and characterized that are responsive to freezing stress. Many studies have suggested that cold regulated gene expression is critical in plants for both chilling tolerance (Hsieh et al. 2002) and cold acclimation (Knight et al. 1999, Tamminen, 2001). The molecular tool makes it possible to select directly at the gene label without waiting for the phenotype to show up. Therefore it is important to use most appropriate tools that help in reaching the goals. The designed genotype should be better than the available ones and must reach the farmers. An attempt has been made in this article to review the various mechanisms and genes involved in cold acclimatization Tele: 01931-238246 E-mail addresses: g_singh72@rediffmail.com © 2011 Elixir All rights reserved ABSTRACT Plants respond with changes in their pattern of gene expression and protein products when exposed to low temperatures. Thus ability to adapt has an impact on the distribution and survival of the plant, and on crop yields. Many species of tropical or subtropical origin are injured or killed by nonfreezing low temperatures, and exhibit various symptoms of chilling injury such as chlorosis, necrosis, or growth retardation. In contrast, chilling-tolerant species are able to grow at such cold temperatures. Conventional breeding methods have met with limited success in improving the cold tolerance of important crop plants involving inter- specific or inter-generic hybridization. Recent full-genome transcript profiling studies, in combination with mutational and transgenic plant analyses, have provided a snapshot of the complex transcriptional network that operates under cold stress. The changes in expression of hundreds of genes in response to cold temperatures are followed by increases in the levels of hundreds of metabolites, some of which are known to have protective effects against the damaging effects of cold stress. Various low temperature-inducible genes have been isolated from plants. Most appear to be involved in tolerance to cold stress and the expression of some of them is regulated by C-repeat/dehydration-responsive element binding (CBF/DREB1) transcription factors. Genetic analysis has revealed important roles for cellular metabolic signals, and for RNA splicing, export and secondary structure unwinding, in regulating cold-responsive gene expression and chilling and freezing tolerance. Numerous physiological and molecular changes occur during cold acclimation which reveals that the cold resistance is more complex than perceived and involves more than one pathway. The findings summarized in this review have shown potential practical applications for breeding cold tolerance in crop and horticultural plants suitable to temperate geographical locations. © 2011 Elixir All rights reserved. A critical review on morpho-physiological and molecular aspects associated with cold stress in plants Gulzar S. Sanghera 1 and V K Sharma 2 1 Shere Kashmir University of Agricultural Sciences and Technology of Kashmir, Rice Research and Regional Station, Khudwani, Anantnag, 192102, Kashmir, India 2 GBPUAT-Hill Campus, Ranichauri, Tehri Garhwal, 249199 Uttarakhand, India. ARTICLE INFO Article history: Received: 3 August 2011; Received in revised form: 23 September 2011; Accepted: 30 September 2011; Keywords Cold Tolerance, Chlorophyll Accumulation, Photosynthesis, Pollen Fertility and Seed Set. Elixir Agriculture 39 (2011) 5065-5075 Agriculture Available online at www.elixirpublishers.com (Elixir International Journal)