Pollen-wall proteins: Exine-held fractions associated with the incompatibility response in cruciferae

During maturation of the pollen in species ofIberis (Cruciferae) materials from the anther tapetum are transferred to cavities of the exine. These sporophytically-derived materials are responsible for the rejection response induced in the stigmatic papillae within 4-6 h. following incompatible pollination, a response which leads to the occlusion of the stigma papillae by the polysaccharide, callose. The rejection reaction can be induced with agar or agarose gels into which pollen-wall materials have been allowed to diffuse, and also with isolated fragments of the tapetum itself taken from anthers of incompatible plants before transfer of its contents to the pollen. Partial fractionation of the exine-held materials using thin-layer gel filtration suggests that the incompatibility reactions are mediated by one or more "recognition" proteins or glycoproteins in a group with molecular weights in the range 10,000-25,000 daltons.The rejection response has been found to be a rapid and sensitive assay for incompatibility in several Cruciferae.