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The effect of osmotic stress on cell growth and phenylethanoid glycosides (PeGs) biosynthesis was investigated in cell suspension cultures of Cistanche deserticola Y. C. Ma, a desert medicinal plant grown in west region of China. Various initial sucrose concentrations significantly affected cell growth and PeGs biosynthesis in the suspension cultures, and the highest dry weight and PeGs accumulation reached 15.9 g l(-1)-DW and 20.7 mg g(-1)-DW respectively at the initial osmotic stress of 300 mOsm kg(-1) where the sucrose concentration was 175.3 mM. Stoichiometric analysis with different combinations of sucrose and non-metabolic sugar (mannitol) or non-sugar osmotic agents (PEG and NaCl) revealed that osmotic stress itself was an important factor for enhancing PeGs biosynthesis in cell suspension cultures of C. deserticola. The maximum PeGs contents of 26.9 and 23.8 mg g(-1)-DW were obtained after 21 days at the combinations of 87.6 mM sucrose with 164.7 mM mannitol (303 mOsm kg(-1)) or 20 mM PEG respectively, which was higher than that of C. deserticola cell cultures grown under an initial sucrose concentration of 175.3 mM after 30 days. The stimulated PeGs accumulation in the cell suspension cultures was correlated to the increase of phenylalanine ammonium lyase (PAL) activity induced by osmotic stress.