Assessment of some urban ornamental plants in southern Iran revealed that they choose one of the two enzymatic or non-enzymatic antioxidants defensive strategies against heavy metals

Abstract

Abstract Heavy metals (HMs) are one of the most important environmental contaminants. One of the effective approaches to reduce this contamination is phytoremediation. The concentration of ten heavy metals (HMs) including arsenic (As), cadmium (Cd), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), lead (Pb), nickel (Ni), tin (Sn), and zinc (Zn) were measured in ten ornamental plants consisting Ficus religiosa, Ficus elastica, Syzygium cumini, Azadirachta indica, Clerodendrom inerme, Conocarpus erectus, Bougainvillea sp., Delonix regia, Dodonaea viscosa, and Phoenix sp. grown in the city of Bushehr, located in southern Iran. The concentration of HMs was determined by ICP-MS. Some physiological parameters (relative leaf water, dry matter, vitamin C, pH, chlorophyll a, b, and total, carotenoid, anthocyanin, total flavonoid, total protein, total soluble carbohydrates, and proline), and antioxidant enzymes [peroxidase (POD) and superoxide dismutase (SOD)] activity were measured. Bougainvillea had greater amount of Zn (61.86 mg/kg D.W.), Cu (45.52 mg/kg D.W.), and Cr (14.71 mg/kg D.W.) than the other HMs. Greatest amount of Co (0.686 mg/kg D.W.), Fe (428.00 mg/kg D.W.), and Ni (6.44 mg/kg D.W.) was obtained in C. erectus. Also, C. inerme had maximum As (0.0087 mg/kg D.W.) and Sn (2.516 mg/kg D.W.). The highest percentage of dry matter (46.03%) in Phoenix, the highest amount of vitamin C (8.50 mg/100 g F.W.), chlorophyll b (7.63 µg/ml), and total flavonoid (3.92 M/g) in S. cumini, and the highest amount of chlorophyll a (14.61 µg/ml), total chlorophyll (21.86 µg/ml), carotenoid (20.83 µg/g F.W.), and anthocyanin (18.81 mg/100 g F.W.) in F. elastica were obtained. The POD activity (1.462 and 1.214 U/g F.W./min) was highest in leaves of C. inerme and F. elastica containing the highest concentrations of As, Sn and Pb, respectively. The SOD activity was high in these two species. Synthesis of osmolytes increased under Co and Sn stresses. D. viscosa was found to contain most total soluble carbohydrates (24.94%) and proline (1.14 µM/g F.W.) concentration compared to other species. The selected plant species followed a defensive strategy (enzymatic or non-enzymatic) against excess of HMs. Overall, shrubs were much more suitable than trees for absorption of HMs, and C. inerme, F. elastica and Bougainvillea are the best plant species in this connection, respectively.