ters, however, these organs can be killed when the frost zone moves below the rhizome layer. Even during rela-Seashore paspalum (Paspalum vaginatum Sw.) is a warm-season tively mild winters, the crowns and rhizomes are suscepturfgrass, best known for its superior salt tolerance. Plants are subject tible to injury due to the cold. Reestablishment of damto injury during winter conditions along the northern boundary of aged turf is expensive both in terms of labor and plant their zone of adaptation. New cultivars that are more tolerant to low temperatures are needed for use in the transition zone. Cold material. Thus, a more complete understanding of the tolerance has been correlated with the degree of unsaturation in tolerance of warm season grasses to low temperatures membrane lipid fatty acids. Unsaturated fatty acids are thought to is needed to improve their utility and extend their range. aid in maintaining membranes in a fluid state necessary for biological Whereas most temperate perennial plants can survive functioning (homeophasic adaptation). The primary objective was extensive exposure to subfreezing conditions, most tropto characterize fatty acid composition of membrane lipids in three ical and a number of subtropical plants have little or no genotypes differing in cold tolerance. A second objective was to invescapacity to withstand freezing temperatures. A plant's tigate changes in fatty acid content in these genotypes during exposure ability to alter its physiology in response to low temperato low temperatures. Cold-treated plants were exposed to a 10-h ture, such that it can survive otherwise lethal temperaphotoperiod at 8؇/4؇C day/night temperatures and light intensity of tures, is called cold acclimation (hardening). The pro-250 mol m Ϫ2 s Ϫ1 photosynthetic photon flux density for 3 wk. Rhizomes and crowns were harvested at 7-d intervals. Total lipids were cess of cold acclimation occurs seasonally when plants extracted and the polar lipids separated by thin-layer chromatography. are exposed to low, nonfreezing temperatures beforeFatty acids were identified by gas chromatography (GC) and mass the onset of winter (Levitt, 1980). Some C4 grasses have spectroscopy. In all three genotypes, the two saturated fatty acids, been shown to cold acclimate (Anderson et al., 1988, palmitic acid and stearic acid, did not change during cold treatment. 1993). The biochemical changes accompanying acclima-The triunsaturated linolenic acid increased significantly during low tion to low temperature include alterations in soluble temperature exposure. The magnitude of change was greater in the carbohydrate content, synthesis, and conformation of finer-textured and more cold-tolerant PI 509018-1 ('SeaIsle1') than in proteins and changes in membrane lipid composition the intermediately cold-tolerant 'Adalayd' or in the cold-susceptible, and fatty acid saturation (Li, 1984; Sakai and Larcher, coarse-textured PI 299042. These findings suggest that accumulation 1987; Hallgren and Oquist, 1990). Many of the new of linolenic ac...

Three genotypes of seashore paspalum, `PI 299042', `Adalayd', and `PI 509018-1' considered to be cold-sensitive, intermediately cold-tolerant and cold-tolerant, respectively, were analyzed to investigate the biochemical basis of cold tolerance. The cultivars were acclimated to 8/4 °C day/night temperatures and rhizomes nodes and crowns were harvested at 7-day intervals over the 4-week experiment. Total lipid was extracted from these tissues, and the fatty acids present in the lipid fraction were identified by gas chromatography. Palmitic acid, stearic acid, linoleic acid and linolenic acid were the major fatty acids present. In cold acclimated tissues, the level of palmitic acid and stearic acid did not change significantly during the treatment period. There was a decrease in the level of linoleic acid by the second week of cold treatment. The amount of linolenic acid increased significantly during the second week of cold treatment corresponding to the decrease in linoleic acid. The change in the amount was significantly greater in `PI 509018-1' than in `Adalayd' or `PI 299042'. These results are similar to what was found for cultivars of bermudagrass that differ in their cold-tolerance phenotypes. Desaturases are enzymes involved in introducing the double bonds into the fatty acid chains. Research is underway to characterize and clone the genes encoding the Ω3, Ω6, and Ω9 desaturases, which may have an important role in affecting the cold tolerance by altering the degree of membrane lipid fatty acid saturation.