Role of reactive oxygen species and antioxidative enzymes in the loss and re-establishment of desiccation tolerance in germinated pea seeds

Abstract

This study highlights the regulatory function of ROS and its detoxifying enzymes during the loss and re-establishment of desiccation tolerance (DT) in PEG pretreated and untreated germinated pea (Pisum sativum L.) seeds with 2 mm long radicles. Dehydration of untreated pea seedlings to initial water content (IWC; 0.11 gH2O g−1 DM) and below IWC (0.06 gH2O g−1 DM) reduced the DT to 60 and 20 %, respectively. Significant amelioration in DT was observed in PEG pretreated seedlings by ∼100 % and 70 % following dehydration at IWC and below IWC, respectively. Rendering DT in the PEG pretreated seedlings was negatively associated with an extensive reduction in superoxide (∼2.3 folds) and H2O2 (∼1.8 folds) levels compared to the untreated seedlings. Enhanced expression, levels (quantitative) and number (isoenzyme) of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) in the PEG pretreated seedlings negatively correlated with the lowering ROS levels and its associated oxidative damage. It is concluded that the re-induction of increased antioxidative capacity is a key factor in the re-establishment of DT in PEG-pretreated pea seedlings. Additionally, PEG pretreatment resulted in 50 % disappearance of superoxide in the sub-apical zone (SZ) of the radicle compared to the radicle of untreated seedlings dehydrated below IWC. Further, in situ detection of superoxide accumulation in the apical zone (AZ) was NADPH-oxidase dependent but in the SZ it was independent of NADPH-oxidase. Our results showed that the osmotic stress induced the expression of antioxidative enzymes in germinated pea seeds and made them desiccation tolerant against oxidative stress caused by desiccation/drought.