Nutrient limitation as a tool for the induction of secondary metabolites with antioxidant activity in basil cultivars

Sweet basil (Ocimum spp.) is an important source of secondary metabolites with a significant diversity of polyphenolic compounds. In order to investigate possibilities of induced synthesis of secondary metabolites under conditions of limited nutrition, four basil cultivars ('Small leaved', 'Genovese', 'Dark Opal' and 'Lemon basil') were exposed to different levels of mineral nutrition (high, medium and low) with two forms of nitrogen (nitrate alone or in combination with ammonium) and under controlled conditions. Nutrient limitation effects have been assessed on lipid peroxidation, the activity of phenylalanine ammonium lyase (PAL), total phenolic content, flavonoid concentration, and total antioxidant activity together with LC-DAD-MS/MS analysis of main phenolic acids in different plant parts. After one month of prolonged nutrient limitation results clearly indicate induced synthesis of assessed metabolites, together with lower lipid peroxidation, higher PAL activity, and prominent antioxidant activity. The results are also cultivar and nutrient specific. The highest content of phenolic compounds (particularly caffeic acid - 1.45 mg g(-1) DW) and the highest antioxidant activity (IC50 = 22.36 mu g ml(-1)) was in extracts from 'Small leaved' basil roots, whereas the highest concentration of rosmarinic acid (61.2 mg g(-1) DW) was in extracts from 'Genovese' basil roots, both under the condition of nutrient limitation. This study provided a novel approach for the higher metabolite production with uniformity of cultivation conditions and lower content of mineral nutrition applied and pointed out to basil roots as a viable source of metabolites of interests.