Overexpression of bacterial catalase in tomato leaf chloroplasts enhances photo‐oxidative stress tolerance
The Escherichia coli gene katE, which is driven by the promoter of the Rubisco small subunit gene of tomato, rbcS3C, was introduced into a tomato ( Lycopersicon esculentum Mill.) by Agrobacterium tumefaciens -mediated transformation. Catalase activity in progeny from transgenic plants was approximately three-fold higher than that in wild-type plants. Leaf discs from transgenic plants remained green at 24 h after treatment with 1 µ M paraquat under moderate light intensity, whereas leaf discs from wild-type plants showed severe bleaching after the same treatment. Moreover, ion leakage from transgenic leaf discs was significantly less than that from wild-type leaf discs at 24 h after treatment with 1 µ M paraquat and 10 m M H 2 O 2 , respectively, under moderate light intensity. To evaluate the efficiency of the E. coli catalase to protect the whole transgenic plant from the oxidative stress, transgenic and wildtype plants were sprayed with 100 µ µ µ M paraquat and exposed to high light illumination (800 µ mol m − 2 s − 1 ). After 24 h, the leaves of the transgenic plants were less damaged than the leaves of the wild-type plants. The catalase activity and the photosynthesis activity (indicated by the F v / F m ratio) were less affected by paraquat treatment in leaves of transgenic plants, whereas the activities of the chloroplastic ascorbate peroxidase isoenzymes and the ascorbate content decreased in both lines. In addition, the transgenic plants showed increased tolerance to the oxidative damage (decrease of the CO 2 fixation and photosystem II activity and increase of the lipid peroxidation) caused by drought stress or chilling stress (4 ° C) under high light intensity (1000 µ mol m − 2 s − − − 1 ). These results indicate that the expression of the catalase in chloroplasts has a positive effect on the protection of the transgenic plants from the photooxidative stress invoked by paraquat treatment, drought stress and chilling stress.