Protoplast isolation and fusion in three Ulmus species

Protoplasts were isolated from cotyledons, callus, and suspension cultures of Ulmus americana L. and U. pumula L. and from cotyledons and callus of U. parvifolia Jacq. using various enzyme solutions. Isolation frequencies (percent protoplasts in a solution containing both protoplasts and broken or damaged protoplasts, but very few intact cells) were usually about 10%; however, for U. pumila cotyledons, protoplast frequencies reached 100%. In a limited number of cases, cell wall regeneration occurred after 4–21 days and cell division after 9–21 days. Finally, U. pumila protoplasts were fused using a PEG–calcium solution.