Effects of Botrytis cinerea and Pseudomonas syringae infection on the antioxidant profile of Mesembryanthemum crystallinum C3/CAM intermediate plant

Mesembryathemum crystallinum plants performing C3 or CAM (crassulacean acid metabolism) appear to be highly resistant to Botrytis cinerea as well as to Pseudomonas syringae. Fungal hyphae growth was restricted to 48 h post-inoculation (hpi) in both metabolic types and morphology of hyphae differed between those growing in C3 and CAM plants. Growth of bacteria was inhibited significantly 24 hpi in both C3 and CAM plants. B. cinerea and P. syringae infection led to an increase in the concentration of H2O2 in C3 plants 3 hpi, while a decrease in H2O2 content was observed in CAM performing plants. The concentration of H2O2 returned to the control level 24 and 48 hpi. Changes in H2O2 content corresponded with the activity of guaiacol peroxidase (POD), mostly 3 hpi. We noted that its activity decreased significantly in C3 plants and increased in CAM plants in response to inoculation with both pathogens. On the contrary, changes in the activity of CAT did not correlate with H2O2 level. It increased significantly after interaction of C3 plants with B. cinerea or P. syringae, but in CAM performing plants, the activity of this enzyme was unchanged. Inoculation with B. cinerea or P. syringae led to an increase in the total SOD activity in C3 plants while CAM plants did not exhibit changes in the total SOD activity after interaction with both pathogens. In conclusion, the pathogen-induced changes in H2O2 content and in SOD, POD and CAT activities in M. crystallinum leaves, were related to the photosynthetic metabolism type of the stressed plants rather than to the lifestyle of the invading pathogen.