**1. Introduction**

230 Soybean Physiology and Biochemistry

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Cruiser ® (thiamethoxam), developed and registered by Syngenta, is a chloronicotinic insecticide, belonging to the class of neonicotinoids for seed treatment and has long residual control for a wide range of chewing and sucking insects present in seeds, soil and leaves (Maienfisch et al., 2001).

Thiamethoxan acts by contact and ingestion and the insect stops eating within 24 h after contact with the insecticide. The primary mode of action involves interference with, or by binding to nicotinic acetylcholine receptors (Maienfisch et al., 2001).

Surprisingly, it has been noticed that the treatment of soybean seeds with Cruiser results in a "stand" more uniform, vigorous and more productive, thus acting on germination.

However, seed germination and seedling development of crops are negatively affected by adverse conditions, such as drought (Davidson & Chevalier, 1987; Passioura, 1988, Soltani et al., 2004), salinity (Hampson & Simpson, 1990; Ramoliya & Pandey, 2003, Soltani et al., 2004, Luo et al., 2005; Athar et al., 2008) and high concentrations of soluble forms of aluminum (Matsumoto, 2000; Echart & Cavalli-Molina, 2001, Rout et al., 2001).

A common characteristic of various stress types is the increased production of reactive oxygen species (ROS), which are generally considered harmful to plant cells (Alscher et al. 1997; Smirnoff, 1993, Richards et al., 1998). The ROS include superoxide radical (O2•-) and hydroxyl (•OH), hydrogen peroxide (H2O2) and singlet oxygen (1O2). There are evidences that increased production of ROS under environmental adversities may induce oxidative stress in plants. It has been reported the induction of oxidative stress under conditions of water stress (Smirnoff, 1993; Alscher et al., 1997), salinity (Rio-Gonzalez et al. 2002; Bor et al., 2003; Athar et al., 2008) and excessive concentrations of aluminum in soils (Tamás et al., 2004).

For protection against ROS, plant cells contain an antioxidant system, including various enzymes, among wich, superoxide dismutase (SOD) and peroxidase (POD) (Fridovich, 1978, Bowler et al., 1992, Foyer et al., 1994; Cataneo et al., 2005; Ferreira et al., 2010). SOD and POD are metalloenzymes acting in the elimination of, respectively, O2• - radical and H2O2 produced in stress conditions. Peroxidases are active in many physiological and development processes and are involved both in consumption, as in the production of H2O2 and other ROS (Silva et al. 1994; McQueen-Mason & Cosgrove, 1994; McQueen-Mason, 1995, Bacon et al. 1997; Amaya et al. 1999; Passardi et al., 2004).

Thus, the aim of this study was to evaluate the effect of Cruiser on the enzymes involved in protection against oxidative stress (SOD and POD) caused by drought, salinity and presence of high concentrations of aluminum during soybean germination.
