EFECTO DE LA REDUCCIÓN DE NITRÓGENO EN EL METABOLISMO DE COMPUESTOS FENÓLICOS EN BROTES DE Castilleja tenuiflora Benth. CULTIVADOS EN BIORREACTOR DE INMERSIÓN TEMPORAL

Abstract

Castilleja tenuiflora Benth. (“hierba del cáncer”) is recommended by the Mexican traditional medicine to treat symptoms associated with cancer, which could be due to accumulation of phenolic compounds, such as flavonoids and phenylethanoids. Nitrogen (N) is an essential element for growth and development of plants and its deficiency causes an increase in the concentration of phenolic compounds and on the activity of key enzymes of its synthesis such as the phenylalanine ammonia lyase (PAL). The aim of this study was to evaluate the effect of the reduction of N on the metabolism of phenolic compounds in C. tenuiflora. Shoots of C. tenuiflora were cultivated in temporary immersion bioreactors with B5 medium and 25.74 mM of total N (control) or reducing the concentration of N at 5% (1.32 mM N), without affecting the nitrate:ammonium rate. The results showed that the reduction of N caused a significant decrease in height and biomass of shoots, total concentration of chlorophyll, as well as their ability to multiply and root formation. The maximum activity of the enzyme PAL was 2.5 times higher in the shoots grown with reduced N (1.45 μmol cinnamic acid equivalents (CAE)/h/mg protein) than in the control (0.36 μmol CAE/h/mg protein). Similarly, the concentration of total phenolics and flavonoids was 1.7 and 1.8 times higher than that obtained in the control, respectively. Also from day 9, under reduced N, shoots accumulated anthocyanins. Methanol extracts were analyzed by HPLC, and found that phenylethanoids verbascoside and isoverbascoside are the main compounds, which mostly accumulated in the shoots with reduced N. The activity of the enzyme peroxidase was higher in the shoots under N reduction suggesting a stress condition. In conclusion, the reduction of N significantly affected the shoot growth of C. tenuiflora. In response to N deficiency stress, the shoots of C. tenuiflora accumulate higher concentrations of total phenolics and flavonoids. Specifically, concentration of phenylethanoid verbascoside and isoverbascoside and, anthocyanins were increased. Changes in the concentrations of the chemical compounds were associated with increased activity of the enzyme PAL.