Performance of bean bruchids Callosobruchus maculatus and Zabrotes subfasciatus (Coleoptera: Bruchidae) reared on resistant (IT81D-1045) and susceptible (Epace 10) Vigna unguiculata seeds: relationship with trypsin inhibitor and vicilin excretion.

Callosobruchus maculatus (Cm) and Zabrotes subfasciatus (Zs) were reared on resistant (IT81D-1045) and on susceptible (Epace 10) cowpea seeds. The emergence of adult insects, total developmental period (TDP) and excretion of trypsin inhibitor and vicilin were determined for both bruchid populations. Parameter evaluation showed that the Zs populations emerged from both seeds had no significant differences in emergence and TDP. The Cm population raised from resistant seeds had lower emergence (5.6+/-1.3%) and delayed TDP (46+/-1.25 days) than those emerged from susceptible seeds. The excretion of defense proteins showed that Zs reared in resistant seeds excreted 1.7 times more trypsin inhibitor, but this did not affect emergence or TDP. Furthermore, Cm population emerged from resistant seeds excreted 7 times higher vicilin and 0.4 times less trypsin inhibitor than that emerged from susceptible seeds. These results indicate that vicilins from resistant seeds are involved to significantly longer TDP (46 days) and also drastic reduction of insect emergence ( approximately 5%) of C. maculatus.

Purification and characterization of an insect alpha-amylase inhibitor/endochitinase from seeds of Job's Tears (Coix lachryma-jobi).

A protein inhibitor of locust gut alpha-amylase was purified from seeds of Job's Tears (Coix lachryma-jobi) using ammonium sulphate precipitation, affinity chromatography on Red Sepharose and reversed-phase HPLC. It consisted of two major isomers, each a dimer of two closely similar or identical subunits of Mr about 26,400, and associated by inter-chain disulphide bonds. These isomers also had closely similar amino acid compositions. The major isomer showed no inhibitory activity against amylases from other sources: human saliva, porcine pancreas, Bacillus subtilis, Aspergillus oryzae and barley malt. The manual DABITC/PITC method was used to determine about half of the amino acid sequence of the major isoform. This showed a high degree of homology with previously reported sequences of endochitinase enzymes from several species (tobacco, potato, barley, bean), and endochitinase activity was demonstrated by following the release of radioactivity from [3H]chitin. This novel combination of functions may be relevant to protection of the grain from insect feeding and fungal infection.

The amino acid sequence of a cereal Bowman-Birk type trypsin inhibitor from seeds of Jobs' tears (Coix lachryma-jobi L.).

The major trypsin inhibitor from seeds of Jobs' tears (Coix lachryma-jobi) was purified by heat treatment, fractional precipitation with (NH4)2SO4, ion-exchange chromatography on DEAE-Sepharose, gel-filtration on Sephadex G-75 and preparative reverse-phase HPLC. The complete amino acid sequence was determined by analysis of peptides derived from the reduced and S-carboxymethylated protein by digestion with trypsin, chymotrypsin and the S. aureus V8 protease. The polypeptide contained 64 amino acids with a high content of cysteine. The sequence exhibited strong homology with a number of Bowman-Birk inhibitors from legume seeds and similar proteins recently isolated from wheat and rice.