Regeneration of shoots from cell suspension-derived protoplasts ofAllium cepa

Callus from pre-selected regenerating lines ofAllium cepa andA. fistulosum were used to initiate cell suspensions. Small clusters of callus selected for greater friability were placed into BDS liquid medium containing 2,4-dichlorophenoxyacetic acid (2,4-D) and 6-benzylaminopurine (BA), and were subcultured biweekly. Rapidly growing, finely dispersed lines were used for protoplast isolation. The highest yields came from 3-4 month old cell suspension lines. Protoplasts were cultured in modified K8P liquid medium. Microcalli recovery depended on the number of weeks the cell suspension had been in culture with highest recovery from 4-5 month old cell suspensions. Microcalli were moved to semisolid media when they were approximately 2 mm in diameter. After 4-6 weeks, embryogenic calli thus recovered were moved to variations of standard onion regeneration media containing picloram and BA. Elongating shoots were obtained from up to 88 % of the microcalli of one line, and 40-50 % of the shoots were further multiplied in culture.