Nitrate Reductase Activity, Iron and Nitrate Concentrations in Spinach Inoculated with Two Species of Pseudomonas under Different Nitrogen Levels

Spinach (Spinacia oleracea L.) has been known as iron rich vegetable but in many cases it not only lacks enough iron but accumulates a high amount of nitrate due to irrigation with polluted water around the cities. It seems that Pseudomonas species could diminish nitrate accumulation by inducing nitrate reductase activity (NRA) and could increase iron uptake by producing siderophore. In a factorial experiment based on randomized complete block design with two factors and three replications, spinach plants were inoculated with bacteria (Pseudomons fluorescens Cha0, P.putida Tabriz and non-bacterial) and treated with three levels of nitrogen (0, 125 and 250 mg N Kg-1 as urea).Statistical analysis showed that with increasing levels of nitrogen in soil from 0 to 250 mg kg-1 nitrate concentration and iron was significantly increased in shoot while shoot nitrate reductase activity had not significant changes. By applying the bacteria, nitrate reductase activity was significantly increased in shoot and the most NRA about 180.51% was observed in plant inoculated with P.putida compared to the non non inoculated treatments. Nitrate concentration showed about 32.98% decrease P.putida compared to control. Also iron concentration, increased up to 40 and 26.85% in shoot in P.putida and P.fluorescens treated plants, respectively compared to the non-bacterial. Based on the result obtained in this study, The highest decrease in nitrate accumulation, the highest nitrate reductase activity and iron cocentration in spinach shoots were achieved by P.putida inoculation.