Carbon and nitrogen metabolism during Dendrobium huoshanense protocorm-like body development in suspension culture

Abstract

The aim of this work was to study carbon and nitrogen metabolism during suspension culture of protocorm-like bodies (PLBs) from Dendrobium huoshanense. No significant lag phase of PLB growth was found, and a maximum biomass of 288.6 g l−1 was obtained at day 30 of culture. Sucrose concentration was halved as PLB growth proceeded, while no change in glucose and fructose levels in the medium was found in the first 3 days, followed by a gradual increase until day 9 of culture. Conversely, sucrose in PLBs accumulated dramatically in the first 6 days of culture, followed by a rapid decrease. At the same time, glucose and fructose content of PLBs increased, then declined after 9 days of culture. Soluble acidic invertase (soluble acidic IT) and alkaline invertase (alkaline IT) were activated after inoculation, and reached the highest value on day 6 and day 18, respectively whereas cell wall-bound invertase (cell wall-bound IT) seemed to be repressed throughout culture. The maximum value of sucrose synthase (SuSy) activity was observed on day 18, while sucrose phosphate synthase (SPS) stayed low and constant from inoculation to the end of culture. Ammonium concentration in the medium decreased rapidly, and was hardly detectable after 12 days, when the rapid utilization of nitrate began. Conversely, ammonium in PLBs showed a sharp increase in the first 3 days of culture, followed a rapid decrease until day 12, corresponding to nitrate depletion. Peaks in glutamine synthase (GS) and glutamate synthase (GOGAT) activity were observed on day 12 and 15, respectively. Nitrate reductase (NR) was repressed in the early culture stage, and activated from day 9 to 15 of culture. These results suggest that soluble acidic IT, alkaline IT, SuSy, GS, GOGAT and NR control carbon and nitrogen metabolism at different PLB growth stages.