**4. Discussion**

268 Soybean Physiology and Biochemistry

**ns**

**ns**

**SOD BRS133 PEG -0,3 MPa**

**ns**

**ns**

**60 72**

**Periods of imbibition (h)**

D0 - Check with water D1 - 100 mL Cruiser/100 kg seeds

**SOD cv. Pintado PEG -0,3 MPa**

**72 84**

**Periods of imbibition (h)**

D0 - Check with water D1 - 100 mL Cruiser/100 kg seeds

Fig. 29. Superoxide dismutase activity (U mg proteína-1) in soybean seeds cv. BRS133 and Pintado treated at recommended dose of Cruiser (D1) and check (D0), under PEG. **ns**: not

Tukey α=0.01

differ significantly for each imbibition period.

**U/mg protein**

Tukey α=0.01

**U/mg protein**

Cruiser used as treatment for soybean seeds cultivars BRS 133 and Pintado, accelerated germination, the effect being more pronounced at twice the recommended level. Therefore, the Cruiser's action on the germination reduces the time for crop establishment in the field, reducing the negative effects of competition with weeds or essential nutrients in the soil.

Have been reported that seed germination and seedling development are delayed by high concentrations of aluminum (Matsumoto, 2000; Echart & Cavalli-Molina, 2001, Rout et al., 2001), salinity (Ashraf & McNeily, 1988; Hampson & Simpson, 1990; Ramoliya & Pandey, 2003, Soltani et al., 2004, Luo et al., 2005) and drought (Davidson & Chevalier, 1987; Passioura, 1988, Soltani et al., 2004).

According to Kochian (1995), Matsumoto (2000) and Rout et al. (2001) high aluminum concentrations inhibit root elongation, being proposed that the effect is due to inhibition of cell division, disjunction of cell wall, inhibition of ions flow, loss of membrane integrity and increased production of reactive oxygen species (ROS).

Aluminum causes a delay in germination of the two soybean cultivars in the control treatment and least in treatment with Cruiser, being more pronounced at higher concentrations of this heavy metal.

Salinity causes growth inhibition, being related to a decrease in extensibility of cell walls in the regions of root expansion (Neumann et al. 1994; Chazen et al., 1995), decreases the hydration of the seed (Allen et al. 1986), affects the physiological activities of the embryo due the toxicity of the absorbed ions (Khan et al., 1989), change the metabolism of carbohydrates (Corchete & Guerra, 1986), proteins (Ramagopal, 1990; Dell'Áquila & Spada, 1993) and nucleic acids (Gomes Filho et al., 1983). These changes make difficult to mobilize seed reserves, delaying the emergence of embryonic tissues, or even become non-viable seed (Rogers et al. 1995; Khan & Ungar, 1997).

NaCl causes a delay in germination but Cruiser reduces the negative effect of salinity on germination of soybean cultivar BRS 133, being more evident higher is the concentration of NaCl. To cultivar Pintado no answer was observed.

Cruiser has no effect on germination of soybean cultivar BRS 133 in conditions of drought, but in the cultivar Pintado, Cruiser accelerates germination being the effect more clear in situations of severe water stress.

The reduction on percentage of seeds germination in water stress conditions is attributed to lower diffusion of water through the integument. Water stress causes a prolongation of the stationary phase of the imbibition due to reduced enzyme activity and, consequently, a smaller meristematic development and delay on radicle protrusion (Falleri, 1994).

Seed germination and seedling development of various cultures decrease, influenced by conditions of low water availability, as reported by Owen (1972); Kiem & Krostad (1981), Davidson & Chevalier (1987); Passioura (1988); Soltani et al. (2004).

According to Soltani & Galeshi (2002) the decrease in germination and seedling development, as effect of environmental adversities, with consequent deficiency on crop establishment can cause: a) decreasing the competitiveness of the crop with weeds; b) less protection of soil surface and subsequently greater loss of soil water through evaporation and therefore, less available water for crop; c) lower light interception and yield potential.

It can also be considered that the loss in germination in situations of water stress might result in lower seedling development in the morning period, when the vapor pressure deficit is low and as result decreases CO2 fixation (Tanner & Sinclair, 1983; Condon et al., 1993).

It was detected in the two soybean cultivars used on this study that Cruiser induced more development of the embryonic axis in presence of aluminum, salinity and water deficit, the effect being less evident with increasing of stress intensity.

The present results suggest it can be considered that Cruiser reduces the negative effects of stressful situations studied on germination of soybean seeds.

ROS generation during germination and root growth is generally accepted as an active physiological process, controlled in plant development (Chen & Schopfer, 1999; Schopfer et al., 2001), whose basal production is increased during conditions of biotic and abiotic stresses.

POD activity results indicate that Cruiser promotes this enzyme activity under stressful conditions, but has no effect on SOD activity during soybean germination under the same conditions.

According to Passardi et al. (2004), the peroxidases can be considered as bifunctional enzymes that can oxidize many substrates in H2O2 presence, but also produce ROS. They can promote cell elongation by ROS generation, or are involved in regulating H2O2 concentration, whose reactions cause restriction of growth.

Lin & Kao (2001) suggested that elevated production of H2O2 in rice roots during osmotic stress is probably involved in cell wall stiffening catalyzed by peroxidase, as explanation for the reduction of root growth. It was also suggested that the increase of peroxidase activity in situations of salinity and water stress induced inhibition of growth (Bacon et al. 1997; Lin & Kao, 2001).

The peroxidases can also participate in the lignification of new xylem elements in the embryo, hypocotyl, radicle and the hydroxyl radical (•OH) produced by its action could help on the break of seed tegument and subsequent cell elongation (Passardi et al., 2004). Amaya et al. (1999), related that the increase on expression of peroxidase associated with cell wall caused higher rates of germination on tobacco seeds, for providing water retention under conditions of osmotic stress induced by NaCl.

Looking at the results of Cruiser's action on the induction of POD activity and compare it with the results of germination determined in the same periods of imbibition and stressful situations, can be generally considered that the increases in germination are related to increased activity of POD, which had one of two consequences:

a) consumption of ROS originated in stressful situations, thereby preventing the damage caused by these molecules on the cell components and their metabolism or

b) increased production of ROS, arising in situations of stress and for Cruiser's action, which would cause the stimulation of cell elongation, promoting greater radicle development.

As Cruiser had no effect on SOD activity, future work should be focused on investigating the action of the insecticide on other enzymes such as catalase, ascorbate peroxidase, glutathione peroxidase and lipoxygenase, participants of the enzymatic complex involved in protection against the oxidative stress triggered by the presence of aluminum, salinity and water deficit. It would also be of interest to investigate the action of Cruiser on activity of peroxidase associated with the cell wall, whereas in this study was determined only the total peroxidase.

#### **5. Conclusions**

Cruiser used in the treatment of soybean seeds cultivars BRS 133 and Pintado:

• accelerates the germination during the process of imbibition, and the effect is more pronounced at twice recommended level.

