Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/1996
Publication Date: N/A
Citation: N/A Interpretive Summary: Pressure is now being applied to reduce the amounts of pesticides applied to growing and stored crops. One way to do this is to develope crops containing natural compounds that can protect the plants from attack by pests. Such natural pesticides occur in barley seeds, but they had previously not been very well characterized. Before plant researchers can increase the amounts of these pesticides to make the plants more resistant to attack, they need to know exactly what they are and how they work. This work was carried out to identify such compounds in barley and to determine how they function. The compounds studied were identified as small proteins that inhibit the activity of one of the enzymes that allows a cereal insect, the yellow meal worm, to use barley grain as food. Two inhibitors were isolated and purified. Both inhibited the alpha-amylase enzyme of the yellow meal worm, but had no effect on similar enzymes from humans or from barley. The inhibitors were shown to be similar to previously studied proteins called defensins, a name they were given because they are toxic to either fungi or to other plant pests. This work indicates that the defensins may protect the plants by impairing the abilities of the insects to eat them. The knowledge gained indicates that plant breeders may be able to develope barleys that are more resistant to insect attack by increasing the amounts of these naturally occurring protein inhibitors in the plant.
Technical Abstract: Barley seeds contain proteins that apparently protect them against attack by microorganisms and insects. Studies of these barley defensive proteins may lead to the development of barleys having improved natural resistance to pests. We have purified two low molecular weight proteins, designated BI 1 and BIalpha2, from barley grain, using ion exchange chromatography and reversed phase and gel permeation HPLC. Both BI 1 and BIalpha2 inhibited insect (yellow meal worm, Tenebrio molitor) alpha-amylase activities. For the T. molitor alpha-amylase, the IC50 values of BI 1 and BIalpha2 were 40 g and 17 ug, respectively. Neither protein inhibited either human salivary alpha-amylase, barley alpha-amylase, or trypsin activities. The N-terminal amino acid sequences of the inhibitors were highly homologous with those of the plant proteins called defensins. The first 20 N-terminal amino acids of BIalpha2 were identical to those of gamma-hordothionin, but neither BI 1 nor BIalpha2 protein showed any homology with the chloroform/methanol (CM) soluble protein amino acid consensus sequence. The two inhibitors therefore apparently comprise another group of low-molecular-weight barley proteins that inhibit the alpha-amylase activities of some insects that attack cereal grains.