Soybean protoplast culture and direct gene uptake and expression by cultured soybean protoplasts

A method was developed for culturing protoplasts freshly isolated from developing soybean (Glycine max L.) cotyledons. First cell divisions were observed within 5 days after protoplast isolation and microcalli, consisting of about 20 cells, were formed within 10 days. Thirty days after protoplast isolation, callus tissues were observed without the aid of a microscope. A 30 to 50% plating efficiency was consistently obtained. Using a polyethylene glycol-electroporation technique, DNA was introduced into these protoplasts. The protoplasts were then cultured to form callus. Chloramphenicol acetyltransferase (CAT) activity was detected in protoplast cultures 6 hours after introduction of a 35S-CAT-nopaline synthase 3' chimeric gene. The highest CAT activity was detected in 3-day-old electroporated protoplast cultures, indicating transient expression of the introduced gene. Some CAT activity was detected in 40-day-old callus cultures and in geneticin (G418) selected callus tissues which also received a chimeric neomycin phosphotransferase II gene, indicating the presence of stable transformants. A control chimeric gene with an inverted 35S promoter failed to produce any CAT activity in this system.