Cold tolerance is the result of complex physiological mechanisms involving many cellular and plant traits. Plants differ in their tolerance to cold (0-15 ºC) and freezing (Say no to plagiarism. Get a tailor-made essay on "Why violent video games should not be banned"? Get an original essay Many species of tropical origin or subtropical are damaged by low non-freezing temperatures and show various symptoms of cold injury such as chlorosis, necrosis or growth retardation. In contrast, cold-tolerant species are able to grow at such cold temperatures. Membrane damage is the consequence major of cold injury forms of membrane damage can occur as a consequence of freezing-induced cellular dehydration, including expansion-induced lysis, lamellar to hexagonal phase II transitions, and fracture jump injury (Steponkus et al. 1993) Cold acclimation by plants is to stabilize membranes against freezing damage by preventing expansion-induced lysis and the formation of phase II hexagonal lipids. This adaptive capacity impacts plant distribution and survival and crop yields. It appears that multiple mechanisms are involved in this stabilization process. The well-characterized one is changes in lipid composition (Steponkus et al. 1993). Second, temperature-induced change in membrane fluidity is another consequence in plants during low-temperature stress and could represent a potential site of sensing and/or damage ( Horvath et al. 1998 , Orvar et al. The adaptation of living cells to cooling temperatures is a function of alteration in membrane lipid composition due to increased fatty acid unsaturation Genetically modified tobacco plants overexpressing the glycerol-3-phosphate acyltransferase (GPAT) gene. chloroplast (involved in the desaturation of phosphatidylglycerol fatty acids) from pumpkin (Cucurbita maxima) and A. Thaliana showed an increase in the number of unsaturated fatty acids and a corresponding decrease in sensitivity to cooling. At low temperature, increased unsaturation of lipids of membrane appears to be crucial for optimal membrane function. Arabidopsis fatty acid biosynthesis mutant (FAB1) with more saturated membranes showed a decrease in photosystem II (PSII) quantum efficiency, chlorophyll content and quantity. of chloroplast glycerolipids. after prolonged exposure to low temperatures (Wu et al. 1997). A triple fatty acid desaturation mutant (fad3-2 fad7-2 fad8) lacking trienoic fatty acids (18:3 or 16:3) produced a FAB1-like phenotype, when plants were subjected to prolonged exposure to low temperatures (Routaboul 2000). Remember: this is just an example. Get a custom paper from our expert writers now. Get a custom essay. Similarly, fad5 and fad6 mutants with more saturated membranes became chlorotic and showed growth retardation during low-temperature incubation (Hugly et al. 1992 ). In addition to membrane unsaturation, it appears that lipid asymmetry in the membrane also contributes to the physical structure of the membrane at low temperature (Gomes et al. 2000). The accumulation of sucrose and other simple sugars that typically occurs with cold acclimation also appears to contribute to membrane stabilization since these molecules can protect membranes from freezing-induced damage in vitro (Strauss et al. 1986, Anchordoguy et al. 1987).