Submitted to: Journal of Applied Horticulture
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/1/2007
Publication Date: 6/15/2007
Citation: Wang, Y., Wisniewski, M.E., Meilan, R., Uratsu, S.L., Cui, M., Dandekar, A., Fuchigami, L. 2007. Ectopic expression of mn-sod in lycopersicon esculentum leads to enhanced tolerance to salt and oxidative stress. Journal of Applied Horticulture. 9(1):3-8. Interpretive Summary: Unfavorable environmental conditions result in reduced crop yields and loss of vigor for perennial crops, such as fruit crops. Exposure of plants to environmental stress results in the formation of reactive forms of oxygen, such as hydrogen peroxide and superoxide radicals. Collectively, these types of oxygen molecules are referred to as Reactive Oxygen Species (ROS). ROS can be very toxic and result in injury to plant membranes, proteins, and DNA. Understanding how plants manage and deal with oxidative stress is a key objective of National Program 302 (Plant Molecular and Biological Processes). Increased resistance to the effects of ROS could result in plants being less injured by many different types of environmental stress. The current research examined whether or not the overexpression of a manganese superoxide dismutase (SOD) gene in tomato could improve its resistance to salt and oxidative stress. SOD is part of an antioxidant system in plants that has evolved to help the plant cope with oxidative stress. This enzyme is responsible for converting ROS to hydrogen peroxide. Results indicated that higher levels of SOD were present in the transgenic lines of tomato compared to the non-transformed wild-type (WT) tomatoes. The transgenic tomato lines were less injured compared to WT plants when exposed to salt and oxidative stress. These results indicate that overexpression of SOD is an approach that can be used to produce plants more resistant to environmental stress. Alternatively, this information can be used as a breeding tool, i.e. plants can be screened for SOD activity. Those plants with naturally higher levels of SOD could be used as breeding material to develop new cultivars of crops that have increased resistance to environmental stress. Further research will explore the effect of overexpression of SOD on other antioxidant enzymes.
Technical Abstract: Production of reactive oxygen species (ROS) is associated with a number of physiological disorders in plants. Superoxide dismutase (SOD) catalyzes the breakdown of superoxide (O2-) into O2 and H2O2 and provides the first line of defense against the toxic effects of elevated levels of ROS. The effect of increased expression of Mn superoxide dismutase (Mn-SOD) on salt stress tolerance was studied using transformed tomato (Lycopersicon esculentum cv. Zhongshu No. 5) plants. Northern blots confirmed expression of the heterologous Mn-SOD in transgenic plants. Strong Mn-SOD enzyme activity was detected by native PAGE in transformed plants. Transgenic plants showed resistance to the superoxide-generating herbicide methyl viologen (MV, 10-4 M). The total SOD activity was one-and one-half to two-fold higher, and APX (ascorbate peroxidase) activity was six-to-seven fold higher in transgenic, than in wild-type (WT) plant under MV stress. Germination of transgenic tomato seeds at a NaCl concentration of 150 mM was greater than of wild-type seeds. When exposed to salt stress, roots of transgenic plants were less stunted and leaf injury was lower than that observed in WT plants. Also, the total APX activity of transgenic plants was four-to-five fold higher than that of WT under NaCl (200 mM) stress.