Biochemical and molecular analyses of cold acclimation in bermudagrass and seashore paspalum

In the U.S. warm-season turfgrasses are grown commercially as far north as the transition zone (200-mile wide region) between the sub-tropical and temperate zones, where they can be exposed to winters severe enough to sustain significant damage to the perennating organs. Hence, it is of interest to select/breed for cultivars tolerant to low temperatures.;Change in membrane lipid fatty acids during low temperature exposure were studied in two bermudagrass genotypes ('Quickstand', a relatively cold-tolerant cultivar and Arizona common, a cold-sensitive seeded variety) and three seashore paspalum genotypes (P1509018-1, cold tolerant; Adalayd, intermediately cold tolerant; and P1299042, cold sensitive).;Plants were exposed 8°C days and 4°C nights, 250 mumol m -2 s-1 PPFD in 10-hour photo period over a three-week period. Total membrane polar lipids were isolated from rhizomes and crowns, and fatty acids were separated and analyzed by gas chromatography for changes in fatty acid composition over the experimental period.;Four major classes of fatty acids made up greater than 95% of the total content. No changes were observed for palmitic and stearic acids. Linoleic acid, showed a decrease during cold hardening, accompanied by an increase in linolenic acid. These alterations occurred more rapidly and to a greater magnitude in the relatively cold tolerant genotypes (i.e., Quickstand and P1509018-1) than in the relatively cold sensitive genotypes (i.e., Arizona common, Adalayd and P1299042). These findings support the concept that an increase in membrane lipid desaturation may be an adaptive response to low temperatures. This suggested that the activity of the desaturase enzymes and/or desaturase gene expression might be cold temperature regulated.;Partial cDNA clones of the three desaturases were obtained by PCR from 'Midiron' bermudagrass. Southern analysis showed that desaturases are encoded by gene families. The stearoyl-ACP (o-9) desaturase gene family is estimated at two to four members while oleoyl (o-6) desaturase and the linoleoyl (o-3) desaturase gene families are estimated at three to five members each. This nuclear organization is consistent with findings from other plant species, and with the ploidy level of the different bermudagrass genotypes.;Expression of the three desaturase gene classes was studied by Quantitative PCR. Steady-state mRNA levels of microsomal o-3 desaturase were up-regulated at least through the fourth day of cold treatment. Omega 9, o-6 and plastidal o-3 desaturase gene members did not appear to be regulated in response to low temperature. Therefore, o-3 desaturase may affect the cold-tolerance phenotype at the level of transcription. An increase in the amount of o-3 transcripts, in response to low temperature, may lead to an increase in the quantity of the active enzyme. Further studies will investigate the correlation between increases in o-3 desaturase mRNA levels, enzyme activity and the accumulation of linolenic acid during cold acclimation.