DEFENSE RESPONSE OF PEPPER (CAPSICUM-ANNUUM) SUSPENSION CELLS TO PHYTOPHTHORA-CAPSICI

Cell suspension cultures of three cultivars of Capsicum annuum L., wit h different degrees of sensibility to the fungus Phytophthora capsici, responded to elicitation by both lyophilized mycelium and fungus filt rate. They showed conductivity changes, browning, production of the ph ytoalexin capsidiol and synthesis or accumulation of pathogenesis-rela ted (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 bo th the plant and the fungus in order to avoid any stress during their combination. The resistant cv. Smith-5, showed a more rapid and intens e response to the elicitor preparations than the sensitive cvs America no and Yolo Wonder. This was particularly evident when the cell suspen sions were elicited with the filtrate, when differences became clearly visible after only 6 h incubation. The greatest rate of capsidiol acc umulation 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 in hibition threshold of fungal growth (300 mu g capsidiol [g dry weight] (-1)) was reached only in the resistant cultivar. The induction of an intracellular glucanase (pI 8.9 and R-f 0.18) and an extracellular chi tinase (pI 5.4 and R-f 0.70) only in the resistant cultivar 24 h after elicitation suggests that these enzymes are involved in the resistanc e to Pytophthora capsici, while other hydrolases common to all three c ultivars form part of a more general defence. The results indicate tha t elicitation of pepper cell suspension cultures by signal molecules f rom P. capsici exhibits properties of a multicomponent dynamic system in which different protective mechanisms play complementary roles in t he overall expression of the defence reaction. We confirm that the dif ferential responses of resistant and susceptible pepper cultivars to P . capsici previously seen in plant stem sections are retained in suspe nsion culture.