Chilling-induced oxidative stress in young sal (Shorea robusta) seedlings

Aerial parts of the chilling-sensitive young sal seedlings showed overproduction of reactive oxygen species (ROS) and thiobarbituric acid reactive substances (TBARS) in response to constant chilling exposure during November to March (9–14.1 °C) in field conditions. Almost 4–6 fold increase in ROS was observed in aerial parts of chilling exposed seedlings than the control seedlings (maintained in greenhouse). Increased formation of ROS was found to be closely associated with the rise in TBARS in leaf (5.8 fold) and shoot (4.8 fold) tissues. On the contrary the leaf and shoot of control seedling and root of both control and chilling exposed seedlings exhibited relatively very low levels of superoxide and TBARS. The chilling exposed seedlings also showed striking weakening in the free radical processing enzyme systems. The low temperatures during November to March resulted in reduced activities of superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (POX) and ascorbate peroxidase (APX) almost by 49, 26, 7 and 78 % in leaves and 65, 46, 9 and 85% in shoots respectively compared to leaves and shoots of control seedlings. Our results indicated that, substantially higher rates of liberation of superoxide and TBARS along with drastic failure of antioxidant enzyme system in chilling sensitive sal seedlings leads to oxidative bursts terminating into irreversible injury in leaves and shoot of these seedlings.