Comparison of various stress responses in oat in compatible and nonhost resistant interactions with rust fungi

The role of extracellular fl-1,3-glucanases and chitinases was investigated in oat leaves after infection with different rust fungi . The oat leaves (Avena sativa L .) were inoculated with the compatible rust Puccinia coronata f. sp . avenae and the two nonpathogens Puccinia recondita f. sp . tritici and Puccinia graminis f. sp. tritici . No alterations in enzyme activities were found in the compatible interaction . In the nonhost interaction with P. recondita ff sp . tritici (1-1,3-glucanase and chitinase activities increased by 100 % 24 h after infection. With P . graminis f. sp . tritici the activities of both enzymes increased about twofold after 48 h . In both nonhost interactions the observed increase in activity was due to the induction of an acidic fl-1,3-glucanase and a chitinase whereas the activity of the basic enzymes did not change . This increase is small compared to other systems and apparently the enzymes are not able to inhibit growth of the different rust fungi . Treatment of noninfected plants with the abiotic stress factor mercuric chloride induced necrosis and production of avenalumins but had no effect on the activities of the two enzymes investigated . In the nonhost systems no alteration of peroxidase activity and no induction of avenalumins could be found . Our results indicate that mechanisms other than the stress responses of oat plants studied so far are active in nonhost resistance .