DETECTION OF IMMUNOLOGICALLY RELATED KUNITZ AND BOWMAN-BIRK PROTEINASE-INHIBITORS EXPRESSED DURING POTATO-TUBER DEVELOPMENT

Antiserum against a potato Kunitz-type proteinase inhibitor (PKPI) exp ressed in Escherichia coli was produced. In immunoblotting assays of p roteins from potato tubers cultured in vitro, three proteins reacted t o the antiserum, two of 20 kDa and one of 10 kDa. Their N-termini were sequenced. While the 20 kDa proteins showed 59 and 90% identity to PK PI, the 10 kDa one had 65% identity to soybean C-II proteinase inhibit or. Characterization of the temporal expression of these proteins show ed that both could be detected from 10 days after induction of tuberiz ation (DAI) in vitro, but the times when maximum amounts of PKPI and 1 0 kDa protein could be detected were different, corresponding to 22 an d 32 DAI, respectively. The amounts of these proteins decreased in the following stages, and no positive reaction of the antiserum with matu re tuber proteins could be found. The 20 kDa proteins were also detect ed in early stages of development of potato tubers grown in the held, indicating that these proteins are expressed during normal tuber devel opment, and differ from the PKPIs reported previously.