Ultrastructural and metabolic modifications at the plant–pathogen interface in Mesembryanthemum crystallinum leaves infected by Botrytis cinerea

Botrytis cinerea infection-induced ultrastructural and metabolic changes in Mesembryanthemum crystallinum performing C3 and CAM photosynthesis were investigated and compared with the defence response. Regardless of the plant photosynthetic carbon metabolism, infection induced hypersensitive response-like necroses that successfully inhibited the fungal growth. To gain an insight into the co-regulation of photosynthesis, the antioxidant defence and carbohydrate metabolism, we studied the infection-induced ultrastructural changes in chloroplasts and metabolic modifications related to the photochemical activity and prooxidant/antioxidant homeostasis. Different patterns of B. cinerea-induced ascorbate-, glutathione- and tocopherol-related changes were found in C3 and CAM leaves indicating that specific mechanisms were involved in regulation of the antioxidant defence. A decrease in photochemical activity visualized by chlorophyll fluorescence imaging was found only in CAM plants. This was accompanied by the ultrastructural dismantling of chloroplasts, increased number of plastoglobules and diminished number of starch grains in chloroplasts. However, in infected C3 plants, showing similar ultrastructural disturbances in the chloroplasts, the photochemical activity and the number of starch grains remained unaffected whereas decreased surface of starch grains were found. We propose that the specific co-regulation of the response to pathogen and photochemical activity, sink/source relations and antioxidant mechanisms found in C3 and CAM plants were possibly related to the different photosynthetic carbon metabolisms.

► We compared the defence response of C3 and CAM plants to pathogen.
► Changes in chloroplast ultrastructure, photochemical activity and antioxidants were studied.
► Photosynthetic carbon metabolism affected responses of C3 and CAM plants to pathogen.