IMMUNOCYTOCHEMICAL LOCALIZATION OF δ-ZEIN IN THE PROTEIN BODIES OF MAIZE ENDOSPERM CELLS

The δ-zein, a minor component of the maize prolamin, shows extensive immunological cross-reactivity with α- and β-zeins. The adsorption of an anti-δ-zein serum sequentially with cross-reacting antigens revealed that only about 18% of the reactivity of the antiserum was directed to epitopes unique to δ-zein. The localization of the various zein classes within the protein bodies of endosperm cells is important to understanding the synthesis, sequestering, and utilization of these storage proteins. Sections of 28 days after pollination (DAP) isolated protein bodies and 18 and 40 DAP whole endosperms were reacted sequentially with whole anti-δ-zein serum and gold-conjugated protein A. The results showed intense gold labeling in the core (inside the peripheral zone) and weak labeling in the periphery of the sections. This localization was not definitive in view of the above-mentioned cross-reactivities. To obtain an unequivocal localization, the whole antiserum was adsorbed with α-, β-, and γ-zeins and rendered monospecific for δ-zein. Immunostaining of protein body sections with monospecific antiserum showed that gold label was exclusively in the core region of the protein body and appeared to be in discrete lines and zones especially in 18 DAP protein bodies. The data from localizations using the monospecific antiserum indicated that δ-zein occurs throughout the core region of the protein body, probably interspersed with α- and β-zeins. The location of δ-zein is consistent with that predicted from its order of degradation during seed germination.