Aspartic proteases (APs) one of the main proteinase classes, have different physiological functions in animals, fungi and viruses. In plants, knowledge of the biological roles of APs is less well developed. An AP has been purified from potato tuber and leaves (Guevara et al., 1999, 2001). In this paper, the changes in the level of AP in response to infection by Phytophthora infestans (P. infestans) and wounding were studied in intercellular washing fluids (IWFs) from tuber disks of two potato cultivars differing in their susceptibility to P. infestans. A differential induction was observed between both cultivars: in the resistant cultivar, induction was higher and faster in infected tissues than in wounded ones. In the susceptible cultivar, a lower and later accumulation was observed than in the resistant cultivar. In addition, AP had a direct inhibitory effect on the germination of cysts of P. infestans and conidia of Fusarium solani. The pattern of accumulation and in vitro activity of AP suggest that this enzyme may have a role in the defense response of potato.
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