Callus formation from Malus x domestica cv. 'Jonathan' protoplasts.

Protoplasts could be successfully isolated and cultured from callus and suspension cultures of Malus xdomestica cv. 'Jonathan'. Protoplast-derived colonies were recovered when the osmoticum (glucose) was gradually reduced in semi-solid 8p medium or by the use of feeder plates. Formation of embryo-like structures was induced from the protoplast-derived callus on media supplemented with IAA and BA. These structures formed roots but plants failed to develop. Protoplasts could be isolated from leaves, but not from stems or petioles. The leaf protoplasts failed to divide.