OICC Press International Nano Letters 2228-5326 5 4 (December 2015) 2015 07 21 Effect of nano-zinc oxide on nitrogenase activity in legumes: an interplay of concentration and exposure time 10.1007/s40089-015-0155-6 EN Praveen Kumar Central Arid Zone Research Institute, Jodhpur, 342003, IN Uday Burman Central Arid Zone Research Institute, Jodhpur, 342003, IN P. Santra Central Arid Zone Research Institute, Jodhpur, 342003, IN Journal Article 2015 07 21 Abstract Experiments were carried out to study the effect of zinc oxide nanoparticles (nano-ZnO) on nitrogenase activity in legumes. In the first experiment, nodulated roots of cluster bean, moth bean, green gram and cowpea were dipped in Hoagland solution containing 1.5 and 10 μg mL −1 of nano-ZnO for 24 h. Nitrogenase activity in cluster bean, green gram and cowpea roots increased after dipping in solution containing 1.5 μg mL −1 nano-ZnO, but decreased in roots dipped in solution containing 10 μg mL −1 nano-ZnO. However, in moth bean roots, nitrogenase activity decreased after dipping in solution containing either concentration of nano-ZnO. In the second experiment, nodulated roots of green gram were dipped in Hoagland solution containing 1, 4, 6, 8 and 10 μg mL −1 nano-ZnO for 6–30 h before estimating nitrogenase activity. Results showed that an interactive effect of nano-ZnO concentration and exposure time influenced nitrogenase activity. The possible reasons behind this effect have been discussed. A model [ A  = 3.44 + 0.46 t  − 0.01 t 2  − 0.002 tc 2 ( R 2  = 0.81)] involving linear and power components was developed to simulate the response of nitrogenase activity in green gram roots to the concentration and exposure time of nano-ZnO.