Arboriculture & Urban Forestry 32(6): November 2006 283 much greater distances and causes further oxidative damage. Unless ROS are detoxified, there is irreversible damage to membrane lipids, proteins, and nucleic acids. Carotenoids (carotenes and xanthophylls) are found inside the chloroplasts where they function as accessory pigments to chlorophyll helping the plant harvest more light during photosynthesis. They also serve as photoxidative pigments (primarily anti- oxidants) by quenching and detoxifying ROS (Hasegawa et al. 2000; Apse and Blumwald 2002; Chinnusamy et al. 2004). In fact, available information strongly indicates that salt tol- erance is linked to ROS scavenging and detoxification (Chin- nusamy et al. 2004). In addition, sucrose and fructose have been shown to function directly to protect leaf cellular struc- ture through scavenging ROS (Hasegawa et al. 2000; Zhu 2001). In experiment 1, higher concentrations of all the major leaf photoxidative carotenoid and xanthophylls pigments were found in sucrose-treated compared to non-sucrose- treated plants at day 15 following the application of salt to tree root systems. In experiment 2, recovery rates of leaf chlorophyll were higher in sucrose-treated trees compared to non-sucrose-treated trees following salt-induced damage to leaf tissue. The combined effect of sucrose and salt on in- creased antioxidant pigment and chlorophyll levels may have significantly contributed to the induction of salt tolerance in both test species at day 15 after salt application (experiment 1) and greater recover rates from salt-induced leaf tissue dam- age (experiment 2). Other mechanisms, not explored in this study, by which sucrose may have induced stress resilience in both English oak and holly include compensation of photo- synthetic impairment by direct carbon feeding, stabilization of protein structure, induction of defense-related genes, and alterations to root rhizosphere microbial populations (see Koch 1996; Fukushima et al. 2001; Sulmon et al. 2004; Per- cival and Fraser 2005 for further details. Within the United Kingdom, deicing salts are directly re- sponsible for the death of many roadside and city trees (Per- cival and Henderson 2002). Remedial measures after salt damage include dilution of the soil with excess water, appli- cation of calcium-based compounds, and/or installation of physical barriers around the tree (Ryan 2005). The practicali- ties of our results indicate that application of sugars to salt- damaged tress may provide an alternative remedial system to aid tree recovery. Importantly, sugars are inexpensive, non- toxic to humans, plants, and animals, and can easily be in- corporated into existing management strategies for the after- care of trees after planting out. In addition, results indicate a protective role of sugars against salt-induced stress. Further studies are ongoing evaluating the protective properties of carbohydrates in trees against a range of environmental stresses frequently encountered in urban landscapes using larger landscape-sized planting material >50 mm (2 in) in diameter. Acknowledgment. The authors are grate- ful for funding in part from the TREE Fund (Hyland Johns Grant). LITERATURE CITED Apse, M.P., and E. Blumwald. 2002. Engineering salt toler- ance in plants. Current Opinion in Biotechnology 13: 146–150. Arntz, A.M., E.H. Delucia, and N. Jordan. 2000. From fluo- rescence to fitness: Variation in photosynthetic rate af- fects fecundity and survivorship. Ecology 81:2567–2576. Basra, A.S., and R.K. Basra. 1997. Mechanisms of environ- mental stress resistance in plants. Publ. Harwood Aca- demic Publishers, UK. 71 pp. Chinnusamy, V., K. Schumaker, and J.K. Zhu. 2004. Mo- lecular genetic perspectives on cross-talk and specificity in abiotic stress signalling in plants. Journal of Experi- mental Botany 55:225–236. Clark, A.J., W. Landolt, J. Bucher, and R.J. Strasser. 1998. The response of Fagus sylvatica to elevated CO2 and ozone probed by the JIP-test based on the chlorophyll fluorescence rise: OJIP, pp. 283–286. In Responses of Plant Metabolism to Air Pollution and Global Change. De Kok J.L., and Stulen, I., Eds. Brackhuys Publishers, Leiden, The Netherlands. ———. 2000. Beech (Fagus sylvatica L.) response to ozone exposure assessed with a chlorophyll a fluorescence per- formance index. Environmental Pollution (Barking, Es- sex: 1987) 109:501–507. Dobson, M.C. 1991. De-icing salt damage to trees and shrubs. Forestry Commission Bulletin 101. Foyer, C., M. Lelandais, C. Galap, and K. Kunert. 1991. Effects of elevated cytosolic glutathione reductase activity on cellular glutathione pool and photosynthesis in leaves under normal and stress conditions. Plant Physiology 97: 863–872. Fukushima, E., Y. Arata, T. Endo, U. Sonnewald, and F. Sato. 2001. Improved salt tolerance in transgenic tobacco expressing apoplastic yeast derived invertase. Plant & Cell Physiology 42:245–249. Garg, A.K., J.K. Kim, T.G. Owens, A.P. Ranwala, Y. Do Choi, L.V. Kochian, and R.J. Wu. 2002. Trehalose accu- mulation in rice plants confers high tolerance levels to different abiotic stresses. Proceedings of the National Academy of Sciences of the United States of America 99:15898–15903. Gibbs, J.N., and C.A. Palmer. 1994. A survey of damage to roadside trees in London caused by the application of de-icing salt during the 1990/91 winter. Arboricultural Journal 18:321–343. ©2006 International Society of Arboriculture
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