Superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) are antioxidant enzymes which have important role in the metabolic reactive oxygen species (ROS) and defence against oxidative stress damage. Antioxidant enzymes activity increases in plant cells as a response to environmental stresses. The objective of this study was to evaluate the effects of micronutrients application on the antioxidant enzyme metabolism (SOD, CAT and GPX) in sunflower under drought stress. This experiment was carried out at Golmakan Agriculture Research Station (Iran) in 2005, using a split plot randomized complete block design with four replications. Irrigation as a main factor at three levels (normal, low stress and high stress) and six micronutrient treatments (control, Fe, Fe+Zn, Fe+Zn+Cu, Fe+Zn+Cu+Mn, Fe+Zn+Cu+Mn+B) as sub-plots within the main plots. Base fertilizers (N,P,K) and micronutrient treatments also used as required on the basis of the soil test. Results showed that the activity of these enzymes was significantly different (a= 5%) between control and stress treatments. The antioxidant enzymes concentrations were increased at 11-31% under high stress. Also there were significant differences (a= 5%) between control and micronutrient treatments under different enzyme concentrations. The antioxidant enzymes concentrations were increased at 48-89% level with Fe+Zn+ Cu+Mn treatment. The results showed that under drought stress micronutrients application increase drought resistance in sunflower.

The use of bio-fertilizers in agro-ecosystems is considered to have the potential to improve plant growth in extreme environments featuring water shortages. However, while arbuscular mycorrhizal fungi (AMF) and bacteria bio-fertilizers have been used in other plants to enhance stress tolerance, little is known about their symbiotic effect on sorghum (Sorghum bicolor L.) growth under drought stress conditions. Therefore the aim of this study was to investigate the inoculation of sorghum with Nitroxin and Glomus mosseae and their interaction effects on the agro-physiological characteristics and grain yield of sorghum under drought stress conditions. Nitroxin is a bio-fertilizer that consists of a mixture of Azospirillum and Azotobacter bacteria. The results showed that co-inoculation of sorghum seeds with Nitroxin and AMF improved the chlorophyll (a, b and total) content, soluble proteins, water use efficiency) WUE(, relative water content (RWC), nitrogen (N) content in the plant, AMF spore density, proline content, grain yield, panicle length, the number of panicles per plant, grain number per panicle, 1000-grain weight and decreased the electrolyte leakage and water saturation deficit (WSD) in drought stress and non-stress conditions. Under drought stress conditions, there was a 27% increase in grain yield under the synergistic effects of bacteria and fungi compared to the non-application of these microorganisms. The results of this experiment show that Nitroxin and AMF bio-fertilizers can mitigate the negative effects of stress on plants in drought stress conditions by increasing the amount of photosynthetic pigments, soluble proteins and osmotic regulation and decreasing electrolyte leakage. We found that the combination of bacteria and AMF for sorghum growth and yield increment is a promising method to cope with the stress caused by drought.

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