Physiological responses of Catharanthus roseus to different nitrogen forms

The responses of carbon and nitrogen metabolisms in the medical plant Catharanthus roseus to the nitrogen solutions (N1, N2 and N3) containing different ratio of nitrate to ammonium (1:0, N1; 1:1, N2; 1:3, N3) were investigated here. The plants in N3 nitrogen solution were strongly inhibited in photosynthetic gas exchange and carbohydrate accumulation, reflecting the toxicity symptom of excess ammonium continuously accumulated in plants. The treatment with N2 nitrogen solution, however, displayed an obviously synergistic effect on plant growth and metabolisms in contrast to nitrate as the sole source. The short-term (7 days) exposure of plants to N2 nitrogen solution resulted in an increased shoot/root ratio, leaf mass ratio, and Pn, as well as the elevated levels of sucrose, glutamate, aspartate, proline and threonine. The plants in N2 nitrogen solution accumulated twofold catharanthine and vinblastine than did the plants in N1 or N3 nitrogen solution after the long-term incubation. Internal nitrate had an increased accumulation in the plants in N2 nitrogen solution compared to the counterparts. The supply of N2 or N3 nitrogen solution to plants for 7 days induced an over tenfold increase of ammonium in leaves as compared to the case using N1 nitrogen solution. The increased ammonium ion promoted the activities of NADH-dependent glutamate dehydrogenase (NADH-GDH) both in the leaf and root of plants. Under the ammonium-containing solution (N2 and N3 nitrogen solutions), there was a significantly increased activity for glutamine synthase (GS) in the root during experiment and for nitrate reductase (NR) in the leaf and root only after 21 days of treatment. The performed correlation analysis revealed a negative relation between soluble sugars and internal ammonium, whereas a positive correlation of alkaloid production with glutamate and aspartate.