β-1,3-glucanase and chitinase as pathogenesis-related proteins in the defense reaction of twoCapsicum annuum cultivars infected with cucumber mosaic virus

Abstract

Pathogenesis-related (PR) proteins from pepper (Capsicum annuum L.) cv. Americano (tolerant) and cv. Smith-5 (sensitive), both elicited by infection with cucumber mosaic virus (CMV), were assayed for chitinase and glucanase activities. Two basic PR-proteins, Mr 49.0 and 28.0 kD, were elicicited from the intracellular fraction (INTRA-F) of both cvs. by CMV infection, while four acidic Mr 15, 19, 36 and 40 kD and two basic Mr 21.2 and 24 kD PR-proteins were elicited from the intercellular fluid (IF) of cv. Americano leaves. Five acidic Mr 21.5, 23.2, 24.4, 25.2 and 36 kD and five basic Mr 23.3, 26, 28.8, 30 and 32.3 kD PR proteins were elicited from the IF of cv. Smith-5. Isoelectric focusing (IEF) of the IF and the INTRA-F proteins revealed the occurrence, in both pepper cultivars, of one acidic Mr 36 kD and one basic Mr 25 kD PR-protein with glucanase activity. After native-PAGE for acidic proteins, the acidic PR-protein of Rf 0.7 and Mr 36 kD present in the IF of both pepper cvs. showed glucanase activity. Native-PAGE for basic proteins of the INTRA-F showed the presence of one band (Rf 0.61, Mr 25 kD) common to both cvs. and two additional bands (Rf 0.49, Mr 26 kD and Rf 0.79, Mr 33 kD) in the cv. Americano with glucanase activity. The specificity shown by the basic PR-proteins suggests glucanase activity is involved in the mechanisms of resistance to CMV in the cv. Americano. There was no difference in chitinase isoform patterns between the two pepper cultivars analyzed. After IEF of the IF proteins, one acidic chitinase isoform was detected. Native-PAGE separation of the IF showed one band (Mr 30 kD) with chitinase activity. Chitinase activity was not detected in the INTRA-F of either cultivar.