Biochemical analysis of enhanced tolerance in transgenic potato plants overexpressing D-galacturonic acid reductase gene in response to various abiotic stresses

Upregulation of the antioxidant enzyme system in plants provides protection against various abiotic stresses. Transgenic potato plants overexpressing the strawberry D-galacturonic acid reductase (GalUR) gene with enhanced accumulation of ascorbate (AsA) were used to study the antioxidant system involving the ascorbate-glutathione cycle in order to understand the tolerance mechanism in plants in response to various abiotic stresses under in vitro conditions. Transgenic potato tubers subjected to various abiotic stresses induced by methyl viologen, sodium chloride and zinc chloride showed enhanced activities of superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.1.1.1.6) and enzymes of the ascorbate-glutathione cycle such as ascorbate peroxidase (APX, EC 1.11.1.11), dehydroascorbate reductase (DHAR, EC 1.8.5.1) and glutathione reductase (GR, EC 1.8.1.7), as well as increased levels of ascorbate, glutathione (GSH) and proline when compared to untransformed tubers. The increased enzyme activities correlated with the mRNA transcript levels in the stressed transgenic tubers. Significant differences in redox status of AsA and GSH were also observed in stressed transgenic potato tubers that showed increased tolerance to abiotic stresses compared to untransformed tubers. This study suggests that the increased accumulation of AsA could upregulate the antioxidant system which imparts improved tolerance against various abiotic stresses in transgenic tubers compared to untransformed tubers.