Optimizing Bioreactor Culture System Of Protocorm-Like Bodies In Dendrobium Candidum

Dendrobium candidum, a precious traditional Chinese herbal medicine belongs to Dendrobium species and is characterized by special pharmacological function and higher medicinal value. In recent years, the wild resource of D. candidum has been severely depleted, and the artificial cultivation development has been inhibited due to the low and unstable efficient compound contents in cultivated plants. Therefore, this study used in vitro cultured protocom-like bodies (PLBs) to investigate the factors affecting PLB growth and bioactive compound accumulation for establishing an optimized bioreactor culture system and providing an alternative material for production of D. candidum products.PLB growth in bioreactor and solid culture was compared, PLB biomass in bioreactor culture was significantly better than in solid culture, PLB fresh and dry weight in bioreactor culture were1.48-fold and1.75-fold more than in solid culture, respectively. To optimize PLB bioreactor culture system, several factors affecting PLB biomass and bioactive compound accumulation were studied. At variable aeration during bioreactor culture, PLB biomass and alkaloid and polysaccharide contents were more favorable than at constant aeration; Inoculation density also had an obvious effect, the maximum growth coefficient was found at30g of inoculation density while the highest biomass at50g of inoculation density, alkaloid and polysaccharide content reached maximum levels at inoculation densities of40and50g.During PLB bioreactor culture, the culture medium was also modified. Sucrose was better than glucose and fructose,30g·L-1sucrose was more suitable when compared with other sucrose concentrations. Favorable PLB biomass and bioactive compound accumulation were found at1/2MS medium contained1.8mM PO43-and30mM NO3-(as sole nitrogen source). PLB growth was promoted at pH5.8and inhibited at the pH levels higher or lower than5.8. Alkaloid and polysaccharide contents were differently affected by pH levels, the maximum alkaloid (330.73μgmg-1) and polysaccharide (574.13mg·g-1) contents were determined at pH4.8and pH7.8, respectively, but the highest yields of both compounds were calculated at pH5.8.The histochemical location of alkaloids and polysaccharides in PLBs and plant leaves and stems was studied by using light microscopy. Both compounds of alkaloids and polysaccarides distributed in parenchymal cells of PLBs but in mesophyll cells of plant leaves. In the plant stem, alkaloids were found in parenchymal cells but polysaccharides were observed around the vascular bundle.