BETA-1,3-GLUCANASE AND CHITINASE AS PATHOGENESIS-RELATED PROTEINS IN THE DEFENSE REACTION OF 2 CAPSICUM-ANNUUM CULTIVARS INFECTED WITH CUCUMBER MOSAIC-VIRUS

Pathogenesis-related (PR) proteins from pepper (Capsicum annuum L.) cv . Americano (tolerant) and cv. Smith-5 (sensitive), both elicited by i nfection with cucumber mosaic virus (CMV), were assayed for chitinase and glucanase activities. Two basic PR-proteins, M(r) 49.0 and 28.0 kD , were elicicited from the intracellular fraction (INTRA-F) of both cv s. by CMV infection, while four acidic M(r) 15, 19, 36 and 40 kD and t wo basic M(r) 21.2 and 24 kD PR-proteins were elicited from the interc ellular fluid (LF) of cv. Americano leaves. Five acidic M(r) 21.5, 23. 2, 24.4, 25.2 and 36 kD and five basic M(r) 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 occurr ence, in both pepper cultivars, of one acidic M(r) 36 kD and one basic M(r) 25 kD PR-protein with glucanase activity. After native-PAGE for acidic proteins, the acidic PR-protein of Rf 0.7 and M(r) 36 kD presen t 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, M(r) 25 kD) common to both cvs. and two additional bands (Rf 0. 49, M(r) 26 kD and Rf 0.79, M(r) 33 kD) in the cv. Americano with gluc anase activity. The specificity shown by the basic PR-proteins suggest s glucanase activity is involved in the mechanisms of resistance to CM V in the cv. Americano. There was no difference in chitinase isoform p atterns between the two pepper cultivars analyzed. After IEF of the TF proteins, one acidic chitinase isoform was detected. Native-PAGE sepa ration of the IF showed one band (M(r) 30 kD) with chitinase activity. Chitinase activity was not detected in the INTRA-F of either cultivar .