Biochemical responses of wheat under oidium attack in the presence of silicon under hydroponic conditions

OSCAR FONTAO DE LIMA FILHO; CARLOS ALBERTO MOLDES; RICARDO ANTUNES AZEVEDO; RUI A. GOMES-JUNIOR; SIU MUI TSAI

Uberlandia

Conferencia; III Conferência Internacional sobre Silicio na Agricultura; 2005

Wheat plants cultivar BR40 were cultivated in Johnson nutrient solution with increasing rates of silicon (Na2SiO3.5H2O): 0; 0.36; 0.89, 1.78 and 3.57 mM. Approximately 30 days after emergency (DAE), a natural infestation of oidium occurred in the greenhouse, which attacked all plants. Visual evaluations at 60 and 63 DAE were carried out in three branches, using the second and first leaves from the main ear. Two different disease analysts scored from 1 to 5 according with James?s scale. The disease symptoms exhibited a gradual decrease as silicon concentration increased in the nutrient solution. At 65 DAE, the first and the second leaves from each treatments were collected and stored at ultrafreezers for polyphenols analysis and determination of the antioxidant enzymes - catalase (CAT), ascorbate peroxidase (APX) and superoxide dismutase (SOD). The lipid peroxidation levels using malondialdehyde (MDA) was also performed. In stress conditions reactive oxygen species (ROS) can accumulate in tissues resulting in CAT, APX and SOD activity alterations and lipoperoxide production. In the aerial parts of the plants, the activities of antioxidant enzymes and lipid peroxidation (MDA) were shown to decrease with the increase in silicon concentration. Furthermore, phenol synthesis in the highest silicon treatment was stimulated. These results suggest that the increase in wheat resistance to oidium, in the sampling period tested, may be of chemical as well as of mechanical nature. The increase in polyphenols in plants with high levels of silicon indicates a probable resistance mechanism of chemical nature, whereas the reduction in antioxidant enzymes activities and lipoperoxidation suggest a protective effect of silicon of mechanical nature.