Influence of γ- radiation stress on scavenging enzyme activity and cell ultrastructure in groundnut (Arachis hypogaea L.)

The biological effect of gamma rays on plant cell is mainly due to interaction with water molecules producing free radicals, which can potentially damage important components of exposed cell. Consequently the balance between the production of Reactive oxygen species (ROS) and quenching activity of scavenging enzymes is upset resulting in oxidative damage. Among the major active oxygen species viz., superoxide radical (O-2), hydrogen peroxide (H2O2), hydroxyl radical (OH) and singlet oxygen (1O2), the H2O2 and OH radicals are most reactive, toxic and destructive. The cell membrane and cellular organelles are the main targets for free radical attack. The aim of this study was to establish changes in the activity of the scavenging enzymes, plant pigments like chlorophyll which confer sensitivity to irradiation stress, and also to assess the damage caused by ionizing radiation on cell membrane and cellular organelles on exposure to gamma radiation. When the groundnut (Arachis hypogaea L.) cv. Narayani seedlings were subjected to gamma rays (0.00, 10, 20, 40, 50 and 100Gy) from a cobalt source (60Co) at a dose rate of 3.06 kGy/hr, a dose dependent increase in the activity of peroxidase (POD) and superoxide dismutase (SOD) was observed in response to free radical generation. Further, gradual decline in leaf chlorophyll content was observed with increased dose and 100Gy exposure resulted in lowest leaf chlorophyll content (0.895mg/g FW) due to maximum pigment deterioration. The gamma ray induced ultra structural changes included distortion of nuclear membrane, chloroplast swelling, thylakoid dilation, rupture of chloroplast outer membrane and swollen endoplasmic reticulum. Damage to ultra structure, accumulated with exposure time and led to both vesiculation in the chloroplast stroma and endoplasmic reticulum of the cells after the exposure to gamma rays at a dose of 100Gy