The isolation and purification of surface specific proteins of somatic and reproductive protoplasts of lily and rapeseed

The plasma membrane surface proteins of intact somatic (leaf) and reproductive (pollen, generative cell or sperm cell) protoplasts of lily ( Lilium longiflorum ) and rapeseed ( Brassica napus cv. Midas) were compared after probing with N-hydroxysuccinimido- (NHS) or sulfo-NHS-biotin. The plasma membranes of intact protoplasts are impermeable to these biotin probes, which bind covalently to the free amino groups of surface proteins. Enzyme-labelled streptavidin was used to detect membrane proteins after separation by SDS-PAGE and western blotting. In lily, six proteins specific to the surface membrane of leaf protoplasts were identified varying from 25–64 kDa, three proteins to pollen protoplasts in the range 35–64 kDa and two proteins to generative cell protoplasts, 63 and 67 kDa. In rapeseed leaf protoplasts, seven proteins in the range 22–69 kDa were detected, while in the sperm enriched fraction five proteins were present in the same kDa range. The proteins identified as membrane specific for generative cell protoplasts of lily have been isolated and were used as antigens for monoclonal antibody production. Preliminary results indicate the successful production of antibodies to surface antigens. These antibodies will be used to localise surface specific epitopes which are likely to be involved in cell-cell recognition at fertilization.