Effect of Molybdenum on Nitrogenase and Ni- Trate Reductase Activities of Wheat Inocu- Lated with Azospirillum Brasilense Grown Un- Der Drought Stress

The effect of Mo on nitrate reductase and nitrogenase activities as well as the growth and mineral nutrition of wheat inoculated with Azospirillum brasilense in greenhouse pot experiments under drought stress conditions was evaluated. Plant dry weight and total N-yield appeared to be drastically affected by the severe drought stress. This inhibition was associated with a decline in nitrate reductase (NR) and nitrogenase (NA) activities of both shoot and root systems. Under severe water stress (35%) low nitrogen-fixing activity and low Azospirillium content were obtained. Mo application affected positively wheat growth, total plant N-yield, saccharides, protein, potassium and magnesium contents both in control and inoculated plants under severe water stress (35%). Nitrate reductase (NR) and nitrogenase (NA) activities in inoculated and uninoculated plants in the absence of Mo declined as a result of water stress injury. Mo application caused a stronger increase in the activity of nitrate reductase compared to nitrogenase activity. Application of Mo led to an increased accumulation of K+ ions up to 2-fold compared to the respective Mo-untreated plants. Our results indicated that Mo could contribute considerably to the tolerance of water deficits in wheat inoculated with Azospirillum. Abbreviations: MoMolybdenum; NRNitrate reductase; NANitrogenase; SMC Soil moisture content; AZAzospirillum brasilense