Physiological mechanism of the enhanced drought tolerance in transgenic poplar (Populus alba × Populus glandulosa) with codA gene

Abstract

Poplar is a tree species with important economic value and ecological function. Investigating the response mechanism of transgenic poplar expressing choline oxidase (codA) gene to drought stress can provide a theoretical basis for the drought tolerance breeding and application of poplar. In this research we studied with a potted experiment the influences of drought stress and rehydration on plant growth, contents of hydrogen peroxide (H2O2), malondialdehyde (MDA), glycine betaine (GB) and antioxidant enzyme activities in leaves of transgenic poplar (T) and wild-type (NT). Results showed that: (1) Plant height and total biomass increased slowly under drought stress condition, while the transgenic poplar plants grew better than NT plants and recovered faster after rehydration. After five weeks of drought stress, the dry weight of shoots and roots in transgenic line decreased by 21.01% and 22.97%, respectively. While, the dry weight of shoots and roots in NT decreased by 47.21% and 52.11%, respectively. Compared with the NT, T plants had higher dry weight of shoots and roots. (2) Under drought stress condition, the contents of H2O2 and MDA in leaves of poplar increased evidently and then decreased, and continued to fall after rehydration, but their contents were higher in the NT plants than in the transgenic poplar plants. Under drought stress condition, the free proline and glycinebetaine content in leaves of transgenic poplar plants were significantly higher than those in NT plants. After three weeks of drought stress, the content of GB in transgenic line was 2.38 folds those in NT plants. (3) The activities of SOD, POD, CAT and APX in leaves gradually increased with the extension of drought time, and then decreased after rehydration; except for POD, the other three antioxidant enzyme activities were significantly higher in transgenic line than those in NT plants. These results indicated that increasing osmotic adjustment substance contents and enhancing the antioxidant enzyme activities could be the intrinsic physiological mechanism of enhanced drought resistance and recovery ability of transgenic poplar.