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Chickpea defensive proteinase inhibitors can be activated by podborer gut proteinases

Author:
Giri, A.P., Harsulkar, A.M., Deshpande, V.V., Sainani, M.N., Gupta, V.S., Ranjekar, P.K.
Source:
Plant physiology 1998 v.116 no.1 pp. 393-401
ISSN:
0032-0889
Subject:
trypsin, protein synthesis, insect pests, trypsin inhibitors, developmental stages, chymotrypsin, inactivation, proteolysis, Helicoverpa armigera, Cicer arietinum, pest resistance, protein composition, seed development
Abstract:
Developing chickpea (Cicer arietinum L.) seeds 12 to 60 d after flowering (DAF) were analyzed for proteinase inhibitor (Pi) activity. In addition, the electrophoretic profiles of trypsin inhibitor (Ti) accumulation were determined using a gel-radiographic film-contact print method. There was a progressive increase in Pi activity throughout seed development, whereas the synthesis of other proteins was low from 12 to 36 DAF and increased from 36 to 60 DAF. Seven different Ti bands were present in seeds at 36 DAF, the time of maximum podborer (Helicoverpa armigera) attack. Chickpea Pis showed differential inhibitory activity against trypsin, chymotrypsin, H. armigera gut proteinases, and bacterial proteinase(s). In vitro proteolysis of chickpea Ti-1 with various proteinases generated Ti-5 as the major fragment, whereas Ti-6 and -7 were not produced. The amount of Pi activity increased severalfold when seeds were injured by H. armigera feeding. In vitro and in vivo proteolysis of the early-and late-stage-specific Tis indicated that the chickpea Pis were prone to proteolytic digestion by H. armigera gut proteinases. These data suggest that survival of H. armigera on chickpea may result from the production of inhibitor-insensitive proteinases and by secretion of proteinases that digest chickpea Pis.
Agid:
665416