Morphological, physiological and biochemical responses to combined cadmium and drought stress in radish (Raphanus sativus L.)

Drought and heavy metal stress are among the most important stress factors that negatively affect plant growth. This study was carried out to determine the individual and combined effects of cadmium (Cd) and drought stress on growth (plant leaf area, stem and root diameter, shoot and root fresh weight, shoot and root dry weight), physiological [electrolyte leakage (EL), leaf relative water content (LRWC)] and biochemical [antioxidant enzyme activity, hydrogen peroxide (H2O2), malondialdehyde (MDA), proline, sucrose and mineral element content] parameters of radish. In the study, four Cd concentrations (0 mg kg(-1), 100 mg kg(-1), 150 mg kg(-1) and 200 mg kg(-1)), three irrigation levels (100%, 75% and 50% of field capacity-FC) were used. Leaf area, stem and root diameter, shoot and root fresh weight, shoot and root dry weight, LRWC, chlorophyll a, chlorophyll b and total chlorophyll content decreased with increased level of drought and Cd stress, but EL has increased. The effect of water deficit on these parameters was more detrimental than heavy metal stress; however, the stress-related damage was greater under combined stress conditions. In addition, H2O2, MDA, proline and sucrose content of radish leaves increased with increased water deficit and Cd stress levels. POD, CAT and SOD enzyme activities of radish leaves under combined stresses increased more than individual stress conditions. There was a significant increase in the content of Cd in the plant leaves and roots under Cd stress compared to the control. This increase in leaves was more pronounced than roots. Although individual drought and Cd stress negatively influenced radish growth and development, the damage was greater with the simultaneous occurrence of these two stress factors.