Ultrastructural localization of Bowman-Birk inhibitor on thin sections of Glycine max (soybean) cv. Maple Arrow by the gold method.

The soybean Bowman-Birk inhibitor (BBI), a polypeptide of MW 8,000, has a specificity directed against trypsin and chymotrypsin. BBI was localized at the ultrastructural level by the protein A gold method on thin sections of Glycine max (soybean) cv. Maple Arrow. In cotyledon and embryonic axis, BBI was found in all protein bodies, the nucleus and, to a lesser extent, the cytoplasm. Contrary to the Kunitz trypsin inhibitor (Horisberger and Tacchini-Vonlanthen 1983), BBI was not present in the cell wall but was found in the intercellular space. Intensity of marking in cotyledons of four-day-old seedlings was similar with the exception of the intercellular space which was free of BBI. In two lines lacking the Kunitz inhibitor (P.I. 157440 and 196168), data indicated that marking intensity was similar to that of cv. Maple Arrow. In contrast, in varieties lacking the lectin (Norredo, T-102) marking was more intense than in cv. Maple Arrow.