Abstract:Protoplasts were isolated and cultured from hypocotyl embryogenic callus tissue of Gossypium hirsutum L. cv. "Lumian 6". The highest yields of viable protoplasts were obtained from a vigorous embryogenic callus 7 to 9 d old subcultured on MS medium supplemented with 2 mg/L IAA and 1 mg/L KT using a solution of 1% cellulase Onozuka R-10, 1% pectinase, 0.7 mmol/L KH2PO4, 2.5 mmol/L Ca2+ , and 0.5 mol/L osmoticum (mannitol), at pH 5.8 and at a temperature of 30 ℃. After separation and purification (in 21% sucrose floatation medium), the protoplasts were laid up in a quiet liquid protoplast culture medium containing K3 salts, NT vitamins with 0.1 mg/L 2,4-D, 0.2 mg/L KT and 0.45 mol/L glucose for 10 to 15 min. The protoplasts were fractioned into an upper and a lower layer in the centrifugal tube. Most of the protoplasts in the lower layer were smaller, round and rich in cytoplasts in which contain many granular substances. When this kind of protoplasts were cultured in the thin liquid protoplast culture medium with a density of 1 x l0s to 5 x los protoplasts/mL, the division and the callus formation of the regenerated cells were easily observed. The first divisions occurred in 3 days and small cell clusters could be seen after 2 to 3 weeks in the culture. At this moment, the addition of the protoplast culture medium with decreased osmoticum once or twice is needed for the continuous protoplasts division to form calli. Regenerated calli, 3 to 5 mm in diameter, were transferred in succession on MS medium with 2 mg/L IAA and 1 mg/L KT for the initiation of embryogenesis. The embryoids germinated on the hormonefree MS medium and a number of plantlets were obtained. It seems that using vigorous embryogenic callus and decreasing osmoticum are the two critical factors for plant regeneration of cotton protoplasts.