Influence of nitrate level on nitrate assimilation in tomato (Lycopersicon esculentum) plants under saline stress

This experiment was conducted to study the effect of salinity and different NO3- concentrations on NO3- uptake, transport, and reduction. To avoid the significant effect of plant size, the main difference from other studies was the short time period of treatment application. Tomato plants (Lycopersicon esculentum Mill. 'Asun') were grown for 11 d in half-strength Hoagland solution (with 7 mmol/L NO3-) in a growth chamber under controlled conditions. After that, the different NO3- treatments were 0.5, 2, and 4 mmol/L NO3-, and saline treatments consisted of two levels of NaCl: 0 (control) and 75 mmol/L. Under control conditions, an increase in NO3- concentration in the nutrient solution resulted in greater NO3- uptake, NO3- xylem flux, NO3- concentrations in tissues, and leaf and root nitrate reductase activity. However, when plants were exposed to salinity for a short period of time and the plant size or the shoot/root ratio was not an additional factor affecting the physiological parameters, the NO3- concentration in the solution slightly affected the different steps of NO3- assimilation.