The identification of an anther specific antigen in Brassica species using a heterologous monoclonal antibody

Abstract

Monoclonal antibody, MAb 69-139-19, raised against sheep sperm, cross-reacted with anther proteins from four Brassica species tested. Early in anther development the MAb weakly detected a polypeptide of ~ 42 kDa. At the mid-maturation stage the MAb still bound weakly to this band but it also detected a polydisperse band of Mr ~ 160-230 kDa. In mature pollen MAb 69-139-19 labelled the polydisperse region of 160-230 kDa very strongly, as well as a faint, but distinct, band of ~ 116 kDa. Immunogold labelling of B. napus L. anthers and pollen grains also showed a differential pattern of labelling. At the early vacuolate stage the MAb recognized an antigen within the tapetum and the microspore cytoplasm and nucleus. During the late vacuolate stage the MAb bound to the tapetal material during transfer to the pollen grain wall, leading to strong labelling of the pollen wall at maturity. In sheep MAb 69-139-19 binds to the postacrosomal region of the sperm (Hou, 1989). The polypeptide present in plants, which contains the epitope recognized by the MAb is likely to be a different protein to that in sheep, but we suggest that it plays a role in sexual reproduction in Brassica. It is possible that as the polypeptide is located in the pollen coat it may be involved in pollen/stigma interactions during pollination leading to successful adhesion and pollen tube germination.