Biochemical Genetics, Vol. 39, Nos. 9/10, October 2001 ( C  2001) Differential Esterase Expression in Leaves of Manihot esculenta Crantz Infected With Xanthomonas axonopodis pv. manihotis ´ Alvaro J ´ ulio Pereira, 1 Ana S´ ılvia Lapenta, 1 Pedro Soares Vidigal-Filho, 2 and Maria de F ´ atima P. S. Machado 1,3 Received 13 Aug. 2000—Final 7 May 2001 The polyacrylamide gel electrophoresis system (PAGE) and inhibition tests for biochemical characterization of α- and β -esterases were used to obtain a func- tional classification of esterases in plants and to show a differential expression of esterases as markers of pathogenesis in cassava plants (Manihot esculenta Crantz). The characterization of α- and β -esterases from leaves of M. esculenta by the PAGE system was possible using an extraction solution containing two phenol-complexing agents (PVP-40 and sodium metabisulfite), three antioxidant agents (EDTA, β -mercaptoethanol, and DTT), and one quinone reducer (ascorbic acid). Fourteen esterase isozymes were detected in young unexpanded leaves of M. esculenta cultivars. The inhibition pattern of α- and β -esterases of M. esculenta showed that Est-9 is an arylesterase, and in the unexpanded leaves of the M. esculenta plants infected with Xanthomonas axonopodis pv. manihotis, the Est-7 β -esterase showed the characteristic staining of an α/ β -esterase. This dif- ferential expression of Est-7 isozyme in young unexpanded leaves of cassava plants can be used as a marker of pathogenesis after infection with X. axonopodis pv. manihotis. KEY WORDS: esterase; cassava blight; bacteriosis; phytophatogenic xanthomonads. 1 Department of Cell Biology and Genetics, State University of Maring´ a, 87020-900 Maringa, Parana, Brazil. 2 Department of Agronomy, State University of Maring´ a, 87020-900 Maringa, Parana, Brazil. 3 To whom correspondence should be addressed. 289 0006-2928/01/1000-0289$19.50/0 C  2001 Plenum Publishing Corporation