Effect of Absence of Seed .ALPHA.-Amylase Inhibitor on the Growth Inhibitory Activity to Azuki Bean Weevil(Callosobruchus chinensis)in Common Bean(Phaseolus vulgaris L.).

Abstract

Individual seeds of 212 common bean cultivars were analyzed by Ouchterlony immunodiffusion method using the antiserum raised against common bean α-amylase inhibitor (CBAI). Two cultivars, Ofuku-5 and Ofuku-8, gave no reaction with the anti-CBAI serum and no inhibitory activity against porcine pancreatic α-amylase. Furthermore, these CBAI-lacking cultivars contained no lectin.'Analysis of F2 seeds from the cross between Ofuku-5 and Taishou-kintoki (CBAI-containing) indicated that the absence of CBAI was recessive to the presence of CBAI and tightly linked to the absence of lectin. In a previous report, we showed that CBAI strongly inhibited the larval growth of Callosobruchus chinensis. Thus, effects of the absence of CBAI on the larval growth of C. chinensis were examined using artificial beans containing seed components of the two CBAI-lacking cultivars and two CABIcontaining cultivars (Taishou-kintoki and Ofuku-1). The flour of the CBAI-lacking cultivars showed weak inhibitory activity on the larval growth compared with that of the CBAI-containing cultivars, although the larvae could not grow in the intact seeds of the CBAI-lacklng cultivars. The role of lectin, which was also absent In the seeds of Ofuku-5 and Ofuku-8, has been implicated with resistance to insects, especially bean weevils. CBAI and the lectin in the seeds of the CBAI-containing cultivars were separated well by extraction with 20mM sodium phosphate buffer solution and subsequent ammonium sulfate fractionation. The feeding tests using the protein fractions separated from the CBAI-lacking cultivars and the CBAI-containing cultivars demonstrated that the absence of CBAI is considerably responsible for the lowering of the growth inhibitory activity of the flour of CBAI-lacking cultivars.