Zoysiagrass (Zoysia spp.) is a common warm-season turfgrass well adapted in use of lawns and golf courses in many regions because of its excellent heat tolerance, density, low pesticide requirements, and minimal maintenance inputs (Patton et al., 2007a, 2007b; Zhang et al., 2009). Expanded use of zoysiagrass could play an important role in making golf courses and home lawns more environmentally friendly and sustainable (Patton and Reicher, 2007). However, the use of zoysiagrasses has been limited by its relatively weak winter hardiness compared with some other C4 turfgrass species, such as bafflograss, and freezing injury in many regions. Freezing temperature may cause damage by forming ice crystals, which result in rupture of cell membranes and cell dehydration (Fry and Huang, 2004; Zhang et al., 2008). Injury during exposure to chilling temperature also results from reduced or defective metabolic defense functions (Karpinski et al., 2002; Thomashow, 1999).
Zoysiagrasses undergo cold acclimation in late fall as temperature drop and photoperiod gets shorter. It has been well documented that increased cold acclimation could improve freeze tolerance of plants, including turfgrasses (Anderson et al., 2003). Plants possess various adaptive mechanisms for surviving freezing temperature such as increases in certain sugars or amino acids, increases in ABA content, and antioxidant capacity (Patton et al., 2007a, 2007b; Rogers et al., 1977; Zhang and Ervin, 2008; Zhang et al., 2009).
Various metabolites (such as proline) may accumulate during cold acclimation (Zhang and Ervin, 2008; Zhang et al., 2006, 2008). Proline, an amino acid, functions as osmoprotectant and antioxidant to protect cell membrane during dehydration. Patton et al. (2007a, 2007b) reported that proline content increased in response to cold acclimation in zoysiagrasses. Bermudagrass (Cynodon L.C. Rich) cultivars with higher stolon proline content exhibited greater freezing tolerance than those with lower proline during the winter (Munshaw et al., 2006).
Decreases in temperature and photoperiod in fall may create an imbalance, so that the energy absorbed through the light harvesting complex exceeds what can be dissipated or transduced by photosystem II (PSII; Karpinski et al., 2002; Zhang and Ervin, 2008). Excess energy may be directed to O2 and result in accumulation of toxic reactive oxygen species (ROS). To protect from oxidative stress, plants have developed efficient antioxidant defense systems to scavenge ROS such as superoxide radicals (O2−), hydrogen peroxide (H2O2), and hydroxyl radicals (HO−.) (McKersie and Bowley, 1997). The SOD (EC 1.15.11), a group of metalloenzymes, can convert O2− to H2O2, and considered as the “primary defense” against ROS (Perl-Treves and Perl, 2002; Zhang et al., 2008). The H2O2 is further reduced to water by the antioxidant enzymes—CAT (EC 188.8.131.52) and APX (EC 184.108.40.206). The CAT, localized in peroxisomes, scavenges H2O2 produced by glycolate oxidase in the C2 photorespiratory cycle (Perl-Treves and Perl, 2002). POD (EC 1.11.17) is also an important antioxidant enzyme for scavenging ROS. Antioxidant enzymes and metabolites have been shown to be associated with freezing tolerance in plants, including bermudagrass (Karpinski et al., 2002; Zhang and Ervin, 2008). Overexpression of a chloroplast Cu/Zn SOD gene increased resistance to chilling stress in tobacco (Gupta et al., 1993).
ABA and H2O2 have been considered as signaling molecules for inducing plant antioxidant defense systems against abiotic stresses (Xiong et al., 2002). Cytokinins exhibit antisenescence and antioxidant function. Heino et al. (1990) reported that ABA deficiency prevented development of freezing tolerance in Arabidopsis thaliana. Stolon ABA accumulation during cold acclimation is associated with freezing tolerance in bermudagrass (Zhang et al., 2008) and zoysiagrass (Zhang et al., 2009), and exogenous ABA increased freezing tolerance of bermudagrass (Zhang et al., 2008). Hu et al. (2006) found that ABA is a key inducer of H2O2 production in maize exposed to drought stress. Hsu and Kao (2010) indicated that ABA-induced leaf senescence of rice seedlings is due to H2O2 accumulation. Prasad et al. (1994) reported that accumulation of ABA and H2O2 protect mitochondria against CI in maize seedlings.
Cytokinins are adenine derivatives characterized by an ability to induce cell division in tissue culture (in the presence of auxin). They also promote shoot initiation, lateral bud growth, leaf expansion, nutrient mobilization, chloroplast differentiation, and activation of shoot meristems and delay senescence (Davies, 2010). Zeatin and zeatin riboside are some of the most important forms of cytokinins. Cytokinins are synthesized in root tips and developing seeds and transported from roots to shoots via the xylem (Davies, 2010). Taylor et al. (1990) measured cytokinin and ABA levels in field- and growth chamber-grown winter wheat plants. They found that ABA level increased, whereas cytokinin level declined during cold acclimation.
Research on changes of ABA, cytokinin, and H2O2 associated with antioxidant metabolism in zoysiagrass is lacking. Very few studies have been reported on antioxidant metabolism associated with cold acclimation and freezing tolerance in zoysiagrass. Investigations concerning the physiological responses of zoysiagrass to cold acclimation treatment would provide valuable selection information for turfgrass breeders and practitioners. The objectives of this study were to examine effect of cold acclimation treatment on the levels of ABA, cytokinin, and antioxidant enzyme activity and to investigate if cold treatment–induced changes of the hormones and antioxidants are associated with freezing tolerance in zoysiagrass.
Anderson, J.A., Taliaferro, C.M. & Martin, D.L. 2003 Longer exposure durations increase freeze damage to bermudagrasses Crop Sci. 43 973 977
Bernt, E. & Bergmeyer, H.U. 1974 Inorganic peroxides, p. 2246–2248. In: H.U. Bergmeyer (ed.). Methods of enzymatic analysis. Academic Press, New York, NY
Cai, Q., Wang, S., Cui, Z., Sun, J. & Ishii, Y. 2004 Changes in freezing tolerance and its relationship with the contents of carbohydrates and proline in overwintering centipedegrass (Eremochloa ophiuroides (Munro) Hack.) Plant Prod. Sci. 7 421 426
Davies, P.J. 2010 Plant hormones: Biosynthesis, signal transduction, and action. 3rd ed. Springer, New York, NY
Dhindsa, R.S. & Matowe, W. 1981 Drought tolerance in two mosses: Correlated with enzymatic defense against lipid peroxidation J. Expt. Bot. 32 79 91
Fry, J.D. & Huang, B. 2004 Applied turfgrass science and physiology. John Wiley & Sons, Hoboken, NJ
Gupta, A.S., Heinen, J.L., Holaday, A.S., Burke, J.J. & Allen, R.D. 1993 Increased resistance to oxidative stress in transgenic plants that overexpress chloroplastic Cu/Zn superoxide dismutase Proc. Natl. Acad. Sci. USA 90 1629 1633
Heino, P., Sandman, G., Lång, V., Nordin, K. & Palva, E.T. 1990 Abscisic acid deficiency prevents development of freezing tolerance in Arabidopsis thaliana (L.) Heynh. Theor. Appl. Genet. 79 801 806
Hsu, Y.T. & Kao, C.H. 2010 Abscisic acid-induced leaf senescence of rice seedlings is due to hydrogen peroxide accumulation Crop Environ. Bioinform. 7 243 249
Hu, X., Zhang, A., Zhang, J. & Jiang, M. 2006 Abscisic acid is a key inducer of hydrogen peroxide production in leaves of maize plants exposed to water stress Plant Cell Physiol. 47 1484 1495
Karpinski, S., Wingsle, G., Karpinska, B. & Hallgren, J. 2002 Low temperature stress and antioxidant defense mechanisms in higher plants, p. 69–103. In: D. Inze and M. Van Montagu (eds.). Oxidative stress in plants. Taylor & Francis, London, UK
Lu, S., Su, W., Li, H. & Guo, Z. 2009 Abscisic acid improves drought tolerance of triploid bermudagrass and involves H2O2- and NO-induced antioxidant enzyme activities Plant Physiol. Biochem. 47 132 138
Man, D., Bao, Y.X., Han, L.B. & Zhang, X. 2011 Drought tolerance associated with proline and hormone metabolism in two tall fescue cultivars HortScience 46 1027 1032
McKersie, B.D. & Bowley, S.R. 1997 Active oxygen and freezing tolerance in transgenic plants, p. 203–214. In: P.H. Li and T.H.H. Chen (eds.) Plant cold hardiness. Plenum Press, New York, NY
Munshaw, G.C., Ervin, E.H., Shang, C., Askew, S.D., Zhang, X. & Lemus, R.W. 2006 Influence of late-season iron, nitrogen, and seaweed extract on fall color retention and cold tolerance of four bermudagrass cultivars Crop Sci. 46 273 283
Nakano, Y. & Asada, K. 1981 Hydrogen peroxide is scavenged by ascorbate-specific peroxidase in spinach chloroplasts Plant Cell Physiol. 22 867 880
Patton, A.J., Cunningham, S.M., Volenec, J.J. & Reicher, Z.J. 2007a Differences in freeze tolerance of zoysiagrasses: I. Role of proteins Crop Sci. 47 2162 2169
Patton, A.J., Cunningham, S.M., Volenec, J.J. & Reicher, Z.J. 2007b Differences in freeze tolerance of zoysiagrasses: II. Carbohydrate and proline accumulation Crop Sci. 47 2170 2181
Patton, A.J. & Reicher, Z.J. 2007 Zoysiagrass species and genotypes differ in their winter injury and freeze tolerance Crop Sci. 47 1619 1627
Perl-Treves, R. & Perl, A. 2002 Oxidative stress: An introduction, p. 1–32. In: D. Inze and M. Van Montagu (eds.). Oxidative stress in plants. Taylor & Francis, London, UK
Prasad, T.K., Anderson, M.D. & Stewart, C.R. 1994 Acclimation, hydrogen peroxide, and abscisic acid protect mitochondria against irreversible chilling injury in maize seedlings Plant Physiol. 105 619 627
Rao, M.V., Paliyathm, G. & Ormond, D.P. 1996 Ultraviolet-B and ozone induced biochemical changes in antioxidant enzymes in Arabidopsis thaliana Plant Physiol. 110 125 136
SAS Institute, Inc. 2004 SAS v.9.1.3. SAS Institute, Inc. Cary, NC
Systat Software 2007 Sigmaplot v.10. San Jose, CA
Thomashow, M.F. 1999 Plant cold acclimation: Freezing tolerance genes and regulatory mechanisms Annu. Rev. Plant Physiol. Plant Mol. Biol. 50 571 599
Taylor, J.S., Bhalla, M.K., Robertson, J.M. & Piening, L.J. 1990 Cytokinins and abscisic acid in hardening winter wheat Can. J. Bot. 68 1597 1601
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. 11 883 889
Zhang, X. & Ervin, E.H. 2004 Cytokinin-containing seaweed and humic acid extracts associated with creeping bentgrass leaf cytokinins and drought resistance Crop Sci. 44 1737 1745
Zhang, X. & Ervin, E.H. 2008 Metabolic defense responses of bermudagrass during acclimation to freezing stress: A review Acta Hort. 783 181 194
Zhang, X., Ervin, E.H. & LaBranche, A.J. 2006 Metabolic defense responses of seeded bermudagrass during acclimation to freezing stress Crop Sci. 46 2598 2605
Zhang, X., Ervin, E.H., Waltz, C. & Murphy, T. 2011 Metabolic changes during cold acclimation and deacclimation in five bermudagrass varieties: II. Cytokinin and abscisic acid metabolism Crop Sci. 51 847 853
Zhang, X., Wang, K. & Ervin, E.H. 2008 Bermudagrass freezing tolerance associated with abscisic acid metabolism and dehydrin expression during cold acclimation J. Amer. Soc. Hort. Sci. 133 542 550
Zhang, J. & Kirkham, M.B. 1996 Enzymatic responses of the ascorbate-glutathione cycle to drought in sorghum and sunflower plants Plant Sci. 113 139 147