Modified Responses To Salt Stress Of Catharanthus Roseus By Exogenously Supplied Nitrogen Forms

The effect of nitrogen content and mixed NO₃^-/NH₄⁺ regime under NaCl stress was essential for plant. Vindoline, vinblastine and catharanthine, three kinds of dimeric alkaloids from Catharanthus roseus in which there are many kinds of alkaloids, has been widely used in the treatment of cancer and received great attention for its metabolism and regulating mechanisms. In this study, we checked the variation rules of vinblastine, vindoline and catharanthine in C. roseus seedlings under different nitrogen to determine its characteristics of alkaloid metabolism.1. Nitrogen metabolism has attracted attention and nitrate is an important source of assimilable nitrogen, many species of plants can incorporate nitrate through the combined action of assimilatory nitrate reductase (NR). In plants, fertilization would decrease the C/N ratio resulting in a surplus of nitrogen, the excess nitrate could be shunted into the biochemical pathways for the synthesis of nitrogen-based secondary metabolites such as alkaloid. Therefore, we investigated the effects of exogenous NO₃^- on the metabolism of vinblastine in Catharanthus roseus (L.) G. Don seedlings. During the treatment of exogenous NO₃^-, NR activity was determined. NR activities both in roots and in leaves were increased, especially NO₃^- at the concentration of 0.12mM compared with 18mM, conformally the alkaloids contents were also increased observably at the concentration of 0.12mM. NR activities in leaves increased more dramatically than in roots owing to more excess NO₃^- in roots were transported to leaves and were assimilated.2. The effect of different nitrogen form in the nutrient solution on growth, C metabolism and N metabolism in C. roseus seedlings was evaluated. Both fresh and dry weights of leaves were significantly higher when a high concentration of NH₄⁺(75%) in the nutrient solution. Increasing of both NH₄⁺and NO₃^- ratio in the nutrient solution reduced photosynthetic (Pn) rate, however the reduction of Pn became more pronounced at nitrogen of 50%NO₃^- + 50% NH₄⁺in the nutrient solution. Soluble sugars such as sucrose and glucose was highest with 50% NO₃^- + 50% NH₄⁺ in the nutrient solution, however fructose was lower at 50% NO₃^- + 50% NH₄⁺ in the nutrient solution. The activity of GS was reduced by increasing NH₄⁺ and then increased at Glu in the solution. Vinblastine and vindoline was higher at 50% NO₃^- + 50% NH₄⁺ in the nutrient solution.Catharanthine was higher at 25% NO₃^- + 75% NH₄⁺ in the nutrient solution.3. Salinization is one of the most important factors that effect the productivity of soil. Growth of C. roseus seedlings is restricted in saline soils but may be improved by nitrogen nutrition. In this study, the effect of different nitrogen form on growth, soluble sugars content, amino acids content and ammonium assimilation enzyme activities of C. roseus seedlings irrigated with saline water, was determined. Plant fresh and dry weights increased under salinity but SLA, LMR and SMR declined. Shoot/root ratio declined under all nitrogen form with saline water. Differences in growth between the four nitrogen regimes and NaCl stress were due to differences in photosynthesis. Activities of NR, GS and GDH increased with salinity in 100%NO₃^-, whereas there was decreased activity of the alternative ammonium assimilation enzyme GDH at 25% NO₃^- + 75% NH₄⁺. The results suggest that the detrimental effects of salinity can be reduced by partial substitution of NO₃^- with NH₄⁺ and that this is due to the lower energy cost of N assimilation with NH₄⁺ as opposed to NO₃^- nutrition. Catharanthine increased under NaCl except at 100% NO₃^-.