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Infection of pepper (Capsicum annuum) plants with Phytophthora capsici led to the accumulation of β-1,3-glucanases in the stem tissues soon after inoculation. After the appearance of the symptoms on the pepper stems, β-1,3-glucanase accumulation became much more pronounced in the resistant (Smith-5 [S-5]) than in the susceptible (Yolo Wonder [YW]) cultivar. β-1,3-Glucanase activity was also detected in the control stems (uninoculated) but only in the resistant cultivar. The direct detection of β-1,3-glucanase on polyacrylamide gels revealed a basic isoenzyme (Rf 0.18) in the intracellular fraction (INTRA-F), which may be associated with the expression of resistance to P. capsici since its activity was detected only in the resistant cultivar. The fact that other basic isoenzymes (Rf 0.70 and 0.61 from the INTRA-F and Rf 0.57 from the intercellular fraction) and one acidic isoenzyme (Rf 0.70 from the intercellular fraction) were detected in both cultivars suggests that these play a less important role in the development of resistance although they appeared earlier and at greater intensity in the resistant cultivar than in the susceptible one. Using degenerate primers and reverse-transcriptase polymerase chain reaction (RT-PCR), β-1,3-glucanase product of approximately 500 bp was obtained and cloned from cv. S-5 total RNA. This was used as a probe on northern blots of RNA extracted from both cultivars at specific times after infection. One transcript, size 2.0 kb, was detected in both cultivars, and accumulated very close to the inoculation site between 1 and 3 days after inoculation, but to a greater extent in the resistant cultivar (S-5) than in the susceptible cultivar (YW). These data suggest that an early and rapid accumulation of β-1,3-glucanase transcript is associated with the defence reaction that develops in pepper stems infected with P. capsici. [ABSTRACT FROM AUTHOR]

Cell suspension cultures of three cultivars of Capsicum annuum L., with different degrees of sensibility to the fungus Phytophthora capsici, responded to elicitation by both lyophilized mycelium and fungus filtrate. They showed conductivity changes, browning, production of the phytoalexin capsidiol and synthesis or accumulation of pathogenesis‐related (PR) proteins with glucanase (EC 3.2.1.39) and chitinase (EC 3.2.1.14) activities. The cultivation medium was optimised for growth of both the plant and the fungus in order to avoid any stress during their combination. The resistant cv. Smith‐5, showed a more rapid and intense response to the elicitor preparations than the sensitive cvs Americano and Yolo Wonder. This was particularly evident when the cell suspensions were elicited with the filtrate, when differences became clearly visible after only 6 h incubation. The greatest rate of capsidiol accumulation occurred after 18 h in the mycelium‐elicited cells and after 12 h in those elicited with the filtrate. These times are the optimal for capsidiol accumulation, and the phytoalexin is produced much more rapidly than it can be excreted into the extracellular medium. The inhibition threshold of fungal growth (300 µg capsidiol [g dry weight]−1) was reached only in the resistant cultivar. The induction of an intracellular glucanase (pI 8.9 and Rf 0.18) and an extracellular chitinase (pI 5.4 and Rf 0.70) only in the resistant cultivar 24 h after elicitation suggests that these enzymes are involved in the resistance to Phytophthora capsici, while other hydrolases common to all three cultivars form part of a more general defence. The results indicate that elicitation of pepper cell suspension cultures by signal molecules from P. capsici exhibits properties of a multicomponent dynamic system in which different protective mechanisms play complementary roles in the overall expression of the defence reaction. We confirm that the differential responses of resistant and susceptible pepper cultivars to P. capsici previously seen in plant stem sections are retained in suspension culture. [ABSTRACT FROM AUTHOR]