Effects of drought stress and its interaction with silicon on stimulates the antioxidant system and lipid peroxidation in fennel (Foeniculum vulgar)

Drought stress stimulates the production of reactive oxygen species (ROS) in chloroplasts. ROS laed to lipid peroxidation and damage to the cell membrane. In the current study, the effect of different concentrations of silicon were examined on oxidative stress caused by drought in fennel plant. The experimental design was a split plot based on RCBD with three replications in which irrigation regimes includingirrigation at 100%, 70% and 40% of field capacity were assigned as main plots and five levels of silicon foliar sprays (0, 2.5, 5, 7.5 and 10 mM) were allocated to sub plots. The experiment was conducted in 2009 at the Zabol University research farm, Zabol, Iran. The results showed that drought stress significantly decreased chlorophyll a, chlorophyll b, carotenoids, leaf relative water content and catalase activity. In drought conditions, malondialdehyde levels and electrolyte leakage showed a 2 -fold increase over the control. Silicon treatment (7.5 mM) accompanied by drought, increased the activity of peroxidase and ascorbate peroxidase, proline and soluble sugars by 18, 25, 14 and 28%, respectively and decreased malondialdehyde and electrolyte leakage by 30 and 28%, respectively over the control, suggesting that silicon spraying (5 and 7.5 mM) could increase the ability of plants in response to drought stress by strengthening the antioxidant system of the plant and increasing osmolytes, and have protective effect against lipid peroxidation, induced by stress.