The combined effects of salinity and nitrogen forms on Catharanthus roseus: The role of internal ammonium and free amino acids during salt stress

AbstractCatharanthus roseus is widely cultivated at the seaside of Hainan island of China for production of vinblastine with anticancer activity. Improving growth of this plant and vinblastine content under saline conditions is one of the agronomic challenges. In this study, we compare the responses of C. rosesus upon nitrate (N1) or ammonium nitrate (N2) nutrition to salinity. Biomass accumulation, reproductive growth, photosynthetic gas exchange, and the concentrations of soluble sugars (SS), free amino acids (FAA), ammonium (NH$ _4^+ $), sodium (Na+), and vinblastine were determined during 3 weeks of treatment in N1‐control, N1‐salt, N2‐control, and N2‐salt plants. The retarded growth caused by salt stress was largely ameliorated by the N2 nitrogen form. One of the reasons for this improved salt resistance in N2‐salt plants was related to the competitive uptake of NH$ _4^+ $ and Na+. The N2‐salt plants displayed a more rapid response to salinity, leading to decreased transpiration rate, well‐kept water relations, and reduced uptake of Na+. The N2‐control plants rapidly increased the concentrations of soluble sugars and free amino acids, such as sucrose, glucose, proline, and threonine in the first week. These compounds may act as compatible solutes to adjust osmotic stress and retain ion homeostasis in salt‐stressed plants. The increased FAA was found to be at the expense of glutamate accumulation, and the activities of nitrogen assimilation enzymes were tightly linked with this process. The medical alkaloid vinblastine in C. roseus was significantly increased in N2‐salt plants in the first week and in N1‐salt ones in the third week compared to their controls. It is concluded that the supplied nitrogen regime modified salinity‐induced vinblastine production in a time‐dependent way, and this process was tightly related to NH$ _4^+ $ status.