A Guide to Establishing Water Potential of Aqueous Two-Phase Solutions (Polyethylene Glycol plus Dextran) by Amendment with Mannitol

A practical guide to calculating the mannitol (MAN) amendment required to achieve the desired water potential (Psi) of polyethylene glycol/dextran (PEG/DEX) aqueous two-phase systems for protoplast purification is presented. The empirically generated equation Psi = 305[PEG'](2)[MAN] + 0.74[PEG'][MAN]T - 103[PEG'][MAN] + 5.6[PEG'](2)T - 623[PEG'](2) - 0.25[PEG']T + 12.7[PEG'] - 0.078[MAN]T - 22.75[MAN]accurately predicts experimental Psi (in bars). [PEG'] indicates the presence of DEX where [DEX] = [PEG]/(0.6-0.4[PEG]). The equation is applicable for these ranges: [PEG'] from 0.047 to 0.13 gram per gram H(2)O; [MAN] from 0 to 0.7 molal; T from 4.5 to 40 degrees C. Actual Psi should differ from derived Psi by no more than 8% for the least negative values to 4% for the most negative values. The Psi for solutions of MAN, of PEG, and of DEX were also determined. Equations to fit data for each were generated. Analyses indicated a significant synergistic effect on Psi when MAN is added to PEG/DEX and, at certain concentrations, between PEG and DEX.