Antioxidant Responses of Ricebean [Vigna umbellata (Thunb.) Ohwi and Ohashi] Seedling under Iso-osmotic Potential of Salinity and Drought Stress

Background: Salinity and drought are the major abiotic stresses and both can cause osmotic imbalances. Drought stress directly results in osmotic stress whereas salinity problem firstly disrupts the water balance and eventually induces ion toxicity which results in cyto-toxicity, metabolic impairment, nutrient imbalance and finally poor crop growth and yield. The co-ordinated up-regulation or constitutive expression of antioxidative system in plants is the main defense in plant against these stresses and thus the present experiment was undertaken to study the antioxidant responses under drought and salinity stress at seedling stage in ricebean (Bidhan 1). Methods: For studying the effect of iso-osmotic potential of salinity and drought stress solutions of NaCI and PEG 6000 with -0.2 MPa (50 mM NaCI and 10% PEG), -0.4 MPa (100 mM NaCI and 12% PEG) and -0.8 MPa (200 mM NaCI and 18% PEG) osmotic potential were used. The experiment was done in the laboratory of Department Plant Physiology, Bidhan Chandra Krishi Viswavidyalaya (BCKV), Mohanpur, Nadia and West Bengal in the year 2017-18 and 2018-19. Result: Under moderate to high intensity of osmotic stresses the leaf proline content decreased. The mild and medium stress treatments induced much higher activity of GPDX and APX in the leaf which then decreased somewhat as the intensity of stress increased. The experiment showed that drought stress was found to produce more drastic effects on seedling growth in ricebean as compared to the salinity stress at iso-osmotic potentials.