Association of a 33-Kilodalton Cysteine Proteinase Found in Corn Callus with the Inhibition of Fall Armyworm Larval Growth

Protein patterns of callus from corn (Zea mays L.) inbreds that are either resistant or susceptible to fall armyworm (Spodoptera frugiperda J.E. Smith) were analyzed by two-dimensional electrophoresis. Fall armyworm larvae reared on callus initiated from resistant inbreds were significantly smaller than those reared on callus of susceptible inbreds. A 33-kD protein found in callus from the resistant inbreds Mp704 and Mp708 was absent in callus from the susceptible inbreds Tx601 and Ab24E. However, a 36-kD protein found in Ab24E callus immunoreacted with polyclonal antibody raised against the 33-kD protein. When Mp704 nonfriable callus changed to friable, larval growth was not inhibited and the 33-kD protein was absent. There was a significant negative correlation between the concentration of the 33-kD protein in the callus and the weight of the larvae feeding on the callus in the F2 progeny of Mp704 x Tx601. The N-terminal amino acid sequence of the 33-kD protein suggested that it was cysteine proteinase. Purification of the 33- (Mp708) and 36-kD (Ab24E) proteins indicated that they were both cysteine proteinases. The 33-kD cysteine proteinase had 7-fold higher specific activity than the 36-kD enzyme.