Study the effect of cadmium on plant pigments and antioxidant compounds of water mint (Mentha aquatica L.), eryngo (Eryngium caucasicum Trautv.) and froriepia (Froriepia subpinnata Ledeb.)

Cadmium is one of the most dangerous heavy elements that naturally or by human activity enter to the soil and causes oxidative stress in plants. Therefore, this study was conducted to evaluate the effect of cadmium on some of the physiological responses of three aromatic plants including water mint (Mentha aquatica L.), eryngo (Eryngium caucasicum Trautv.) and froriepia (Froriepia subpinnata Ledeb). In three experiments greenhouse, five concentrations of cadmium in soil containing 0, 5, 10, 15 and 20 mg cadmium/kg soil was investigate in a completely randomized design with four replications at Sari University of Agricultural Sciences and Natural Resources, 2017. Seedlings of the all three plants were planted in pots of cadmium contaminated. In before flowering stage Chlorophyll a, b, carotenoid, phenol, flavonoid and antioxidant capacity of shoots were measured. Results showed that leaf pigment in the three all plants decreased linearly with increasing cadmium level, but carotenoid have the lower reduction of compared to chlorophyll a and b. Also chlorophyll b was more sensitive than chlorophyll a to cadmium. While, flavonoid, phenol and antioxidant capacity of plants increased with increasing cadmium levels. Water mint had the average highest phenol (65.89 mg/g), flavonoid (146.88 mg/g) and antioxidant activity (98.49%) than other two plants. Overall, the results showed that plant pigments were affected by cadmium toxicity, and as these plants are rich in antioxidant compounds, the increase of these compounds with increment of cadmium stress is a kind of defence mechanism of three plants for conflict with stress.