Zoysiagrass (Zoysia spp.) is a common turfgrass used for golf course fairways and tees in southern and transition zone climates because of its good heat and drought tolerance and low requirement for maintenance (Fry et al., 2008). ‘Meyer’ has been the predominant commercial cultivar used in the transition zone since its release in 1952 because of its relatively fine leaf texture compared with common Z. japonica, and its excellent freezing tolerance (Grau, 1952; Grau and Radko, 1951). Several high-quality cultivars, including ‘Cavalier’ (Engelke et al., 2002a), ‘Diamond’ (Z. matrella) (Engelke et al., 2002b), and ‘Palisades’ (Z. japonica) (Engelke et al., 2002c), have been developed and released by researchers at Texas A&M University; however, poor freezing tolerance has limited their use in the transition zone (Morris, 1996; Patton and Reicher, 2007).
Physiological contributors to freezing tolerance in Zoysia spp. have been evaluated, but the results are inconclusive. For example, Rogers et al. (1975) reported accumulation of total nonstructural carbohydrate and starch during cold acclimation in ‘Meyer’ in a field study. In contrast, Patton et al. (2007a) reported decreased starch concentrations in zoysiagrass acclimated under controlled conditions. Fuller et al. (1999) concluded that starch and sucrose were not reliable indicators of zoysiagrass cold tolerance, whereas Patton et al. (2007a) observed a negative correlation between starch content and freezing tolerance. Recently, research showed that proline, proteins, and abscisic acid (ABA) are associated with Zoysia freezing tolerance (Patton et al., 2007a, 2007b; Zhang et al., 2009). More information is needed regarding physiological contributors to freezing tolerance in Zoysia spp. to assist in selection and development of high-quality, cold-tolerant cultivars.
Membranes are the primary sites of freezing injury in plants (Steponkus and Wiest, 1978). During freeze-induced dehydration, plasma membranes and chloroplast membranes may form a hexagonal II phase (HII), which compromises membrane integrity and cell function (Cullis and De Kruijff, 1979; Uemura and Steponkus, 1997, 1999). Thus, during cold acclimation, changes in lipid composition take place to preserve the membrane bilayer structure, fluidity, and function (Alberdi and Corcuera, 1991). Research has shown that polar lipids change when plants are exposed to stress such as drought, oxidative assaults, or extreme temperatures (Chen et al., 2006; Li et al., 2004; Selstam and Öouist, 1990; Styer et al., 1996; Toivonen et al., 1992; Wang, 2005). Higher concentrations of polar lipids were observed in woody evergreen leaves (Nothofagus dombeyi) from plants grown at high altitudes (LT50 = −10.2 °C) compared with those grown at lower altitudes (LT50 = −5.0 °C) (Alberdi et al., 1990). Furthermore, dominant lipids in N. dombeyi, digalactosyl diacylglycerol (DGDG), monogalactosyl diacylglycerol (MGDG), and phosphatidylglycerol (PG), increased 200% to 400% during cold acclimation. Welti et al. (2002) observed higher phosphatidylcholine (PC) and lower phosphatidic acid (PA) contents in Arabidopsis thaliana with enhanced freezing tolerance after cold acclimation at 4 °C for 3 d or exposure to −8 °C. In other studies, no relationship has been reported between membrane changes and freezing tolerance (Senser and Beck, 1984; Uemura and Steponkus, 1994).
Fatty acid unsaturation levels are associated with cold hardiness in plants. Unsaturated fatty acid content was higher in bermudagrass (Cynodon spp.) and seashore paspalum (Paspalum vaginatum) cultivars that were more cold tolerant (Cyril et al., 2001, 2002; Samala et al., 1998). Changes in membrane composition and their association with freezing tolerance in turfgrass, and specifically zoysiagrass, have not been measured. Our objective was to compare differences in rhizome polar lipid classes in less hardy Z. matrella ‘Cavalier’ and more hardy Z. japonica ‘Meyer’, and to determine their potential role in freezing tolerance.
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Zhang, Q., Fry, J., Pan, X., Rajashekar, C., Bremer, D., Engelke, M. & Wang, X. 2009 Cold acclimation of Zoysia japonica and Z. matrella and changes in rhizome abscisic acid levels Intl. Turfgrass Soc. Res. J. In press