Influence of different proportion of nitrate, ammonium and silicium on activity of antioxidant enzymes and some physiological traits in sunflower under conditions of salt stress.

The effect of sodium chloride, silicium and different proportions of ammonium and nitrate on photosynthetic rate, antioxidant enzyme activity, chlorophyll content, proline accumulation, relative water content and protein content of sunflower was studied in hydroponical conditions. Salinity was induced by 200 mM NaCl solution. Also, silicium was applied in three levels; 0, 2 and 4 mM. The plants were nourished by different proportions of nitrate and ammonium for supplying nitrogen (NO 3 :NH 4 ratios 100:0, 75:25, 50:50 and 25:75). The results showed that salinity stress decreased photosynthesis, chlorophyll content and relative water content while it increased antioxidant enzyme activity and soluble protein content. Silicium application increased photosynthesis, enzyme activity, chlorophyll and protein content but it had no significant effect on relative water content. The highest photosynthesis was observed in plants treated with 25:75 ratios. Moreover, this ratio increased enzyme activity; while it had no significant effect on chlorophyll, relative water content and soluble protein.