Interaction of nitrogen stress and salicylic acid on the physiological characteristics of borage

Deficiency of nitrogen may lead to decrease in yield and yield potential of crop plants. An experiment was done under glasshouse conditions in order to investigate nitrogen levels and salicylic acid interaction on some physiologic traits of borage (Borago officinials L.). In this experiment various levels of nitrogen (including; 27.5, 55, 110, 220 and 330 mg/L from ammonium nitrate) and salicylic acid (including; zero, 400, 800 and 1200 µM) was used. The results indicated that stomatal conductance, photosynthesis rate, respiration rate, chlorophyll a, chlorophyll b, carotenoids, proline, and ascorbate peroxidase, were increased by increasing of nitrogen level. However, intercellular CO2 concentration, anthocyanin, flavonoids, soluble carbohydrates, catalase, and peroxidase were decreased. Among nitrogen levels, the maximum effect was obtained by 220 and 330 ppm treatments. Furthermore, salicylic acid spraying led to promote stomatal conductance, photosynthesis rate, transpiration rate, photosynthetic pigment content, proline, anthocyanin, flavonoids, soluble carbohydrates, and catalase, peroxidase and ascorbate peroxidase enzyme, but not intercellular CO2 concentration. The highest values of stomatal conductance, photosynthesis rate, transpiration rate, photosynthetic pigment content, proline, anthocyanin, flavonoids, soluble carbohydrates, and activities of catalase, peroxidase, and ascorbate peroxidase enzymes were achieved by 800 and 1200 µM concentrations of salicylic acid and 330 ppm of nitrogen. The results showed that appropriate concentrations of salicylic acid can recover nitrogen shortage and improve the measured traits.