NITRATE is one of the major sources of nitrogen for the growth of plants. It is taken up by plant roots and transported to the leaves where it is reduced to nitrite in the. The main objective of this research was to investigate stimulatory effects of sodium NITRATE, potassium NITRATE, ammonia and urea on the production/generation of the NITRATE REDUCTASE mRNA in Triticum aestivum plants. The plants were grown in standard nutrient solution for 21 days and then starved in a media without NITRATE for seven days. Starved plants were stimulated with various concentrations of sodium NITRATE, potassium NITRATE, ammonia and urea, and the expression of NITRATE REDUCTASE mRNA was analyzed by real-time PCR. Our results indicated that starvation caused significant decrease in the production of NITRATE REDUCTASE mRNA in the plant leaf. Sodium and potassium NITRATE were capable of restoring the production of NITRATE mRNA in a dose-dependent manner, since 50 mM of each produced the highest level of the mRNA. The stimulatory effect of potassium NITRATE was higher than sodium NITRATE, while ammonia and urea did not show such activity. At low concentrations, sodium NITRATE and potassium NITRATE caused significant increase in the NITRATE/nitrite mRNA production, whereas high concentrations of these salts suppressed the expression of this gene considerably.

Lettuce is one of the best accumulators of heavy metals and NITRATE between leafy vegetables. Through this research, it was tried to decreased cadmium absorption with humic acid (HA) and studies the effect of HA on the accumulation and metabolism of NITRATE. Plants were grown in the peat/perlite and irrigated with Hoagland solution with addition of cadmium (2 and 4 mg L-1) and HA (100 and 1000 mg L-1). Results showed that Cd in media increased Cd of leaves and decreased protein and fresh weight but it has not any effect on the N, P and NITRATE concentration and NITRATE REDUCTASE activity. With increasing concentration of HA, increasing in fresh weight, N, protein concentration and decreasing in Cd concentration in leaves was observed. Using of HA and Cd together in nutrient solution showed that HA decreased absorption of Cd. So toxic effect of Cd decreased on the physiological changes of lettuce and do not accumulate NITRATE in leaves, as well. More investigations should be done for using HA on the polluted soil for planting of lettuce.

With the increased usage of NITRATE fertilizers, the removal of their stable ionic and water-soluble end products is a challenge for human health. Several physicochemical methods have been examined for NITRATE removal of water, but biological treatments are mostly preferred due to a higher efficiency and lower cost. To remove nitrogen from water, we investigated the potential of NITRATE-reducing halophilic and halotolerant bacteria. A total of 50 strains from different saline and hypersaline environments of Iran, including the Incheboron wetland, Aran-Bidgol salt-lake, and Urmia endorheic salt-lake, were screened for NITRATE REDUCTASE production. Among investigated bacteria, 60% and 19% of strains obtained from Urmia lake, and Incheboron wetland produced NITRATE REDUCTASEs, respectively. The NITRATE REDUCTASE coding genes narG, and napA were analyzed in all strains with confirmed NITRATE-reducing capacity. The napA gene was successfully amplified from a gram-negative halophilic strain, and the narG gene was detected in ten halophilic strains. Among NITRATE-reducing isolates with the narG gene expression, the Kocuria rosea strain R3A34 showed the highest NITRATE REDUCTASE production level. This strain was selected to optimize for its denitrifying activity. Results showed that 32° C, pH 7. 0, NaCl 8% (w/v), and mannitol (as a carbon source) provide the optimal environmental conditions for the efficient production of NITRATE REDUCTASE by the Kocuria rosea strain R3A34. As these are compatible with wastewaters conditions, this bacterium can be a proper candidate for bioremediation of wastewaters from NITRATE pollutants.

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 as well as chemical fertilization. It seems that Pseudomonas species could diminish NITRATE accumulation by inducing NITRATE REDUCTASE activity (NRA) and could increase iron uptake by producing siderophore. To achiev this purpose, in a factorial experiment based on randomized complete block design with two factors and three replications, spinach plants were inoculated with bacteria (Pseudomons fluorescens ChaO, 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 and iron concentrations were significantly increased in shoot while shoot NRA had not significant changes. By applying the bacteria, NITRATE REDUCTASE activity, significantly increased in shoot and the most increase of NRA (~180. 51% ) was observed in plants inoculated with P. putida compared to the non-inoculated treatment. NITRATE concentration showed about 32. 98% decrease in P. putida compared to the control. Also iron concentration, increased up to 40 and 26. 85% in shoot and 8. 09 and 9% in root 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 and the highest NRA and iron concentration in spinach shoots were achieved by P. putida inoculation.

This study has been conducted to evaluate the effect of different levels of nitrogen on NITRATE REDUCTASE activity, NITRATE content and vegetative growth (based on shoot and root dry weight) in selected Iranian land races of spinach. The experiment ws carried out in 2010-2011 as factorial design under randomize complete blocks in Agriculture College of Shahid Chamran University of Ahvaz. Seedlings of 10 land races of spinach were subjected to three nitrogen treatments (modified Hoagland solution with recommended level of KNO3 as control, Hoagland solution with two or three- fold level of KNO3). Results showed that NITRATE REDUCTASE activity in leaves of ‘Gorgan’ and ‘Kerman’ land races were higher than other land races. In leaves of ‘Tonekabon’, ‘Zanjan-1’, ‘Sari-1’, ‘Sari-2’, ‘Khoor Abad- Qom’, NITRATE REDUCTASE activitywere lower than other land races. NITRATE REDUCTASE activity at control (1 M KNO3) and two or three fold KNO3 level were significantly different in roots all land races.There was significant differences in root or shoot NITRATE accumulation among the plants of all land races treated with different concentrations of KNO3.When grown under control or KNO3 treatment (2 M), plants of ‘Gorgan’ had the highest content of  NITRATE in shoot followed by plants of ‘Sari-1’ and ‘Saqri-2’ treated with KNO3 (3M). The results ofpresent study demonstrate that increasing nitrogen is highly effective in the metabolism of NITRATE in roots and leaves of Iranian spinach land races. These differences may be important for selecting of a spinach land race as an efficient genotype for NITRATE metabolism.

Nitrogen is considered as an essential nutrient for plants and could be taken up in large amounts by plants. Nitrogen fertilizers are known to have beneficial effects when added to pistachio and other fruit trees. But the nitrogen assimilation of Pistacia species in response to salinity, including uptake and NO-3 reduction, has not been well understood. In this study, NITRATE REDUCTASE activity, total amino acids, NITRATE, calcium and sodium accumulation were evaluated in seedlings of Pistacia vera L. ̒ Badami Zarand̕ in response to sodium chloride (0, 75, 150 mm) and calcium NITRATE (0, 10, 15 mm). Results showed that by increasing the level of salinity, NITRATE REDUCTASE activity in leaves and the concentration of NITRATE, total amino acids and calcium (Ca2+) were reduced in the leaves and roots of P. Vera seedlings. Calcium NITRATE induced a significant increase in both the root and leaf NITRATE and total amino acids or NITRATE REDUCTASE activity in leaf under NaCl stress. Calcium NITRATE, also, significantly increased root/ leaf total amino acids ratio and decreased Na+/Ca2+, ratio in the roots. Results showed that salinity affects the NITRATE assimilation in P. Vera plants. Also, results suggest an efficient salt protective mechanism in P. Vera seedlings mediated by free total amino acids and calcium ions

Every organism has different potential to accumulate NO3- from the environment. NITRATE reduction processes are perhaps most significant in maintaining water quality by alteration of NITRATE to nitrite. A comparative study between the NITRATE REDUCTASE NR activity of green and blue green algae in presence of heavy metals is being conducted to present a situation where NITRATE REDUCTASE process may be affected in presence of heavy metals. Metals interacted negatively with the NITRATE REDUCTASE activity of a blue green alga, Anacystis nidulans and green algae, Chlorella vulgaris in both free and immobilized state. The activity was more repressed in C. vulgaris in presence of Ni compared to Zn and Cd. However, Cd was more toxic to NR activity in A. nidulans (free state). Metal dependent variation between free and immobilized cells were found to be significant (P< 0.01) however, the concentration dependent pattern in the activity between free and immobilized state was non significant in both the test organisms. C.vulgaris is more efficient in conversion of NITRATE to nitrite compared to A.nidulans in presence of heavy metals.

Hyoscyamus is one of the medicinal plants, rich in tropane alkaloids. In this research the effects of NITRATE and ammonium on production of secondry metabolites and other physiological parameters, were investigated. The results indicated that when NITRATE and ammonium were both present in nutrient solution and ammonium concentration was lower than NITRATE, dry and fresh weight of root and shoot increased. However, by increasing ammonium concentration, plant growth decreased. With increased concentrations of ammonium, root/shoot ratios were decreased.NITRATE REDUCTASE activity increased in both NITRATE and ammonium fed plants.However, the higher ratio of ammonium to NITRATE led to a decreased NRA. Alkaloid content (sum of hyoscyamine and scopolamine) increased in both NITRATE and ammonium fed plants. However, the higher the ratio of ammonium to NITRATE, the lower the alkaloid content.

Leafy vegetables play a crucial role in human dietary. Excessive application of nitrogen fertilizer leads to accumulation of high levels of NITRATE in the tissues and causes further consequence. In order to evaluate the impact of zinc and harvest times on the reduction of NITRATE accumulation and NITRATE REDUCTASE activity, an experiment was conducted as completely randomized design with factorial arrangement and three replicates in Hoagland and Arnon nutrient solutions. Treatments were two levels of zinc (7 and 50 mg.L-1), two harvest times (29 and 46 days) and two plants of lettuce and spinach. The results indicated that with increasing zinc concentration, NITRATE concentration in lettuce shoots in both times decreased and NITRATE concentration in roots decreased during the second harvest, whereas no reduction was found in roots and shoots of spinach plants. NITRATE REDUCTASE activity was increased in lettuce and spinach plants with application of high zinc levels. Reduced enzyme activity, and increased NITRATE accumulation was observed over time in both experimental plants. The results of this study indicated that NITRATE metabolism in plants affected by activity of NITRATE REDUCTASE enzyme, the species of plant, harvest time and plant nutrients such as the zinc.