Aggregation of plant protoplasts by artificial lipid vesicles

Sonicated unilamellar lipid vesicles, consisting of egg lecithin, stearylamine, and cholesterol in 7:2:1 molar ratios, promoted the aggregation of tobacco (Nicotiana glutinosa) protoplasts with the aid of mono- or divalent cations.A reaction mixture containing liposomes (0.4 micromoles lipid per milliliter), 50 millimolar CaCl(2), 0.5 molar mannitol, and 5 x 10(5) protoplasts per milliliter resulted in approximately 25% protoplast aggregation. To achieve the maximum protoplast aggregation, 1.6 x 10(8) liposomes per protoplast per hour would be required.The kind of liposomes effective in protoplast aggregation were positively charged, small-size vesicles which were obtained either by 60-minute sonication or by membrane filtration in conjunction with sonication.