Vegetative growth, physiological and enzymatic responses of purslane medicinal plant (Portulaca oleracea) to cadmium concentrations the soil

Cadmium is one of the most commonly used heavy metals in the contaminated areas which entered in the ecosystem and the food chains and will have ecological harmful effects on living organisms. Considering the risk of increasing heavy elements in agricultural soils and subsequent exposure to medicinal plants such as purslane (Portulaca oleracea L.), a factorial experiment was conducted in a completely randomized design with three replications. The aim of the presented study was to study the vegetative growth response and the physiological and enzymatic parameters of this medicinal plant in comparison with the increase of cadmium concentration (0 to 275 mg/kg) in the soil. The results showed that vegetative traits, photosynthetic pigments, soluble protein content and relative water content of leaf decreased with increasing cadmium concentrations while increased the levels of malondialdehyde, hydrogen peroxide and proline. Also, the changes in the activity of the three enzymes of peroxidase (POX), ascorbate peroxidase (APX) and superoxide dismutase (SOD) increased at lower levels of toxicity while decreased at higher levels. Purslane was more sensitive to higher levels of cadmium, so that gradient of more studied variables like dry weight of vegetative organs, the photosynthetic pigments, proline, soluble protein and hydrogen peroxide at low levels of cadmium (ranging from zero up to 60 mg/kg) was lower and then continued with a more slope. Overall, the results showed that the purslane medicinal plant has the ability to grow up to 275 mg per kg of cadmium in the soil. However, at concentrations higher than about 60 mg, the accumulation of dry matter and the functioning of the plants defense systems decreased by more than 50%.