Effects of Nitrogen Sources on Nitrate Reductase Activity and Some Physiological Parameters in Psyllium （Plantago ovata F.） under Salinity Stress

The effects of three nitrogen sources （ammonium, nitrate and ammonium＋nitrate） and three salt treatments （0, 100 and 200 mM NaCl） on nitrate reductase activity, proline, soluble protein and carbohydrate contents in psylliom （Plantago ovata） plants were Studied. The nitrate reductase activity tended to increase when NO3- was included in the root-zone solution, but decrease as salinity increased. All N sources stimulated plant growth and nutrient uptake. Shoot and root dry matter tended to decrease as salinity increased, but less so when both NH4＋ and NO3- were present. Shoot biomass accumulated to significantly greater quantities under the mixed-N treatments than when produced using either NH4＋ or NO3- N-form alone. Although not statistically significant, the root biomasses showed a similar tendency. Generally, leaf proline and soluble shoot carbohydrate contents increased with increasing salinity in contrast to soluble protein which decreased regardless of the N source. Under salinity conditions, the concentration of Na＋ in shoot and root tissues was highest in ammonium-N treatment, while that of K＋ was highest in the mixed-N treatment.