Immunocytochemical localization of phenolic compounds in pollen walls using antibodies against p-coumaric acid coupled to bovine serum albumin

Two different antibodies against bovine serum albumin (BSA)-p-coumaric acid-conjugates were produced and used to localize phenolic compounds in exines of pollen from different species. p-Coumaric acid (pC) was coupled to BSA either via the carboxy group (BSA-pC) or directly to the aromatic ring system (BSA-azo-pC). The polyclonal antibodies raised in rabbits were characterized by ELISA with homologous and heterologous antigens using turkey ovalbumin as carrier protein. The results showed that the two immune sera directed against BSA-pC and BSA-azo-pC, respectively, were specific for p-coumaric acid and structurally similar compounds. Only a very poor binding by acetic acid-ovalbumin-conjugates gates and no binding by turkey ovalbumin was detectable. The antibodies reacted with partially purified pollen walls and with highly purified exines. The intensity of the immune reaction was proved to be dependent upon the pollen source and the preparation of the pollen walls. Using light and electron microscopy, it was shown for the first time that, in the exines of Cucurbita maxima, antibody binding was predominantly observed in the region of the germ pore apertures, the outer foot layers, and in the micro- and macrospines. We conclude from this and other earlier published data that phenols are important structural compounds of sporopollenin.