All plants are exposed to environmental stress at some time during their life cycle. Plants respond to such stress by regulating the expression of genes ultimately responsible for synthesis of compounds that help in adapting to the stress. Cold temperature is an important stress affecting crops in the U.S. Some plants are more tolerant to low temperature stress than others, and many of these "acclimate" to withstand previously lethal low temperatures. Acclimation is a naturally occurring physiological process in many temperate perennial plants. In addition to synthesis of compounds like osmolytes and cryoprotectants, the degree of unsaturation of membrane lipid fatty acids contributes to the ability of these plants to withstand prolonged exposure to low temperature. Bermudagrass is a warm season turfgrass, which shows an increase in the synthesis of the tri-unsaturated fatty acid, linolenic acid during cold-acclimation. In addition, there is concomitant decrease in the amount of the di-unsaturated fatty acid linoleic acid. There are cultivar-specific differences in the timing and magnitude of these changes, but the basic pattern is the same. We are currently cloning the omega-3 and omega-6 desaturase genes, of the fatty acid biosynthetic pathway leading to linolenic acid. We used a PCR-based cloning method, with degenerate primers, to clone members of the omega-3 and omega-6 desaturase gene families. Gene family sizes will be determined by genomic Southern blot analysis. Full-length cDNA clones will be obtained by rapid amplification of cDNA ends (RACE). A genomic library, in lambda EMBL3, will be screened to obtain the full-length gene clones. Expression patterns of the desaturase genes in different tissues/organs, during cold acclimation, also will be investigated.

Key words: bermugadrass, cold acclimation, DNA sequence, fatty acid desaturase, gene expression