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 220.127.116.11) and APX (EC 18.104.22.168). 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.
BerntE.BergmeyerH.U.1974Inorganic peroxides p. 2246–2248. In: H.U. Bergmeyer (ed.). Methods of enzymatic analysis. Academic Press New York NY
CaiQ.WangS.CuiZ.SunJ.IshiiY.2004Changes in freezing tolerance and its relationship with the contents of carbohydrates and proline in overwintering centipedegrass (Eremochloa ophiuroides (Munro) Hack.)Plant Prod. Sci.7421426
DaviesP.J.2010Plant hormones: Biosynthesis signal transduction and action. 3rd ed. Springer New York NY
DhindsaR.S.MatoweW.1981Drought tolerance in two mosses: Correlated with enzymatic defense against lipid peroxidationJ. Expt. Bot.327991
FryJ.D.HuangB.2004Applied turfgrass science and physiology. John Wiley & Sons Hoboken NJ
GuptaA.S.HeinenJ.L.HoladayA.S.BurkeJ.J.AllenR.D.1993Increased resistance to oxidative stress in transgenic plants that overexpress chloroplastic Cu/Zn superoxide dismutaseProc. Natl. Acad. Sci. USA9016291633
HeinoP.SandmanG.LångV.NordinK.PalvaE.T.1990Abscisic acid deficiency prevents development of freezing tolerance in Arabidopsis thaliana (L.)Heynh. Theor. Appl. Genet.79801806
HsuY.T.KaoC.H.2010Abscisic acid-induced leaf senescence of rice seedlings is due to hydrogen peroxide accumulationCrop Environ. Bioinform.7243249
HuX.ZhangA.ZhangJ.JiangM.2006Abscisic acid is a key inducer of hydrogen peroxide production in leaves of maize plants exposed to water stressPlant Cell Physiol.4714841495
KarpinskiS.WingsleG.KarpinskaB.HallgrenJ.2002Low 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
LuS.SuW.LiH.GuoZ.2009Abscisic acid improves drought tolerance of triploid bermudagrass and involves H2O2- and NO-induced antioxidant enzyme activitiesPlant Physiol. Biochem.47132138
ManD.BaoY.X.HanL.B.ZhangX.2011Drought tolerance associated with proline and hormone metabolism in two tall fescue cultivarsHortScience4610271032
McKersieB.D.BowleyS.R.1997Active 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
MunshawG.C.ErvinE.H.ShangC.AskewS.D.ZhangX.LemusR.W.2006Influence of late-season iron, nitrogen, and seaweed extract on fall color retention and cold tolerance of four bermudagrass cultivarsCrop Sci.46273283
PattonA.J.CunninghamS.M.VolenecJ.J.ReicherZ.J.2007aDifferences in freeze tolerance of zoysiagrasses: I. Role of proteinsCrop Sci.4721622169
PattonA.J.CunninghamS.M.VolenecJ.J.ReicherZ.J.2007bDifferences in freeze tolerance of zoysiagrasses: II. Carbohydrate and proline accumulationCrop Sci.4721702181
Perl-TrevesR.PerlA.2002Oxidative stress: An introduction p. 1–32. In: D. Inze and M. Van Montagu (eds.). Oxidative stress in plants. Taylor & Francis London UK
PrasadT.K.AndersonM.D.StewartC.R.1994Acclimation, hydrogen peroxide, and abscisic acid protect mitochondria against irreversible chilling injury in maize seedlingsPlant Physiol.105619627
RaoM.V.PaliyathmG.OrmondD.P.1996Ultraviolet-B and ozone induced biochemical changes in antioxidant enzymes in Arabidopsis thalianaPlant Physiol.110125136
SAS Institute Inc.2004SAS v.9.1.3. SAS Institute Inc. Cary NC
Systat Software2007Sigmaplot v.10. San Jose CA
ZhangQ.FryJ.PanX.RajashekarC.BremerD.EngelkeM.WangX.2009Cold acclimation of Zoysia japonica and Z. matrella and changes in rhizome abscisic acid levelsIntl. Turfgrass Soc. Res. J.11883889
ZhangX.ErvinE.H.2004Cytokinin-containing seaweed and humic acid extracts associated with creeping bentgrass leaf cytokinins and drought resistanceCrop Sci.4417371745
ZhangX.ErvinE.H.LaBrancheA.J.2006Metabolic defense responses of seeded bermudagrass during acclimation to freezing stressCrop Sci.4625982605
ZhangX.ErvinE.H.WaltzC.MurphyT.2011Metabolic changes during cold acclimation and deacclimation in five bermudagrass varieties: II. Cytokinin and abscisic acid metabolismCrop Sci.51847853
ZhangX.WangK.ErvinE.H.2008Bermudagrass freezing tolerance associated with abscisic acid metabolism and dehydrin expression during cold acclimationJ. Amer. Soc. Hort. Sci.133542550
ZhangJ.KirkhamM.B.1996Enzymatic responses of the ascorbate-glutathione cycle to drought in sorghum and sunflower plantsPlant Sci.113139147