Reactive oxygen species, lipid peroxidation, protein oxidation and antioxidative enzymes in dehydrating Karanj (Pongamia pinnata) seeds during storage

We investigated the storage behaviour of karanj (Pongamia pinnata L. Pierre), a very popular tree valued for medicinal and biodiesel use, seeds at ambient conditions (27-30 °C and RH 45%). Fresh karanj seeds, showing 100% germination were shed with water content of 0.22 gH2O g− 1 DM. The karanj seeds exhibited intermediate storage behaviour as the percent germination dropped from 100 to 80% when the seeds desiccated below critical water content i.e. 0.11 gH2O g− 1 DM. The loss of germination index (GI) and viability, and increase in solute leakage preceded the loss of germinability. Dehydration mediated decline in seed viability and vigour was negatively associated with accumulation of reactive oxygen species (ROS, like superoxide radical and H2O2). In dehydrating seeds, excess amounts of ROS mediated cellular damage by oxidizing biomolecules like lipids and proteins. The activities of antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) were higher in the 100% viable seeds, and reduced with dehydration induced viability and vigour loss. The expression of specific isoenzymes of SOD (band 1) and CAT (band 2) detected only in seeds exhibiting higher germination, may be considered as markers for seed quality.