Common antigens and male-female recognition in plants

Abstract

THE question of how the female stigma of the plant recognises a pollen grain carrying a compatible male gamete from all the possibilities presented to it by air currents and visiting insects is an intriguing problem¹. When pollen is recognised at the stigma surface, a mixture of components, including proteins and glycoproteins, are released from cavities in the pollen walls^2,3. These components have been partially characterised^4,5 and include those essential to the recognition process⁶. The pollen wall components flow over and bind to the stigma surface which is covered by a secreted sticky coating⁷. The binding of specific recognition factors determines the success of a mating⁸. We have attempted to identify factors involved in poller-stigma recognition, using immunochemical methods with rabbit antisera to pollen and stigma surface components. The major antigen of the stigma surface shows immunological identity and has the same molecular weight as an antigenic pollen wall component. This stigma antigen is also partially identical with components of other tissues of the same plant. Absorption experiments show that the cross-reacting antibodies can be removed from the antisera, leaving antibodies which interact only with the immunising antigen. This raises the question whether plant cells, like animal cells⁹, are specified according to their family, species, organ and tissue by surface determinants.