preparations are passed through a 45 lm stainless steel or
nylon mesh screen to remove undigested cell clumps and
debris from broken cells. Protoplast-containing filtrates are
then centrifuged for 4–10 min at 100g in 15 ml calibrated
screw-top centrifuge tubes. The supernatant is removed
with a Pasteur pipette, and the pellet containing the protoplasts
is gently resuspended in 5 ml of a 25% sucrose
solution containing CPW nutrients (27.2 mg/l KH2PO4,
100 mg/l KNO3, 150 mg/l CaCl2, 250 mg/l MgSO4,
2.5 mg/l Fe2(SO4)3.6H2O, 0.16 mg/l KI, 0.00025 CuSO4,
pH 5.8) (Frearson et al. 1973). This is followed by slowly
pipetting 2 ml of a 13% mannitol solution (containing
CPW salts) directly on top of the sucrose layer (avoid
mixing). Centrifuge for 6 min at 100 g. Viable protoplasts
form a band at the interface between the sucrose and the
mannitol. Carefully remove the protoplasts from this
interface and resuspend them in the appropriate volume of
BH3 medium in preparation for somatic fusion.