Physiological and Biochemical Responses of Capsicum annuum L. Seedlings to Cadmium Stress

Purpose To explore the indexes of physiological and biochemical responses to cadmium (Cd) stress on the growth, photosynthesis and oxidative stress of capsicum (Capsicum annuum L.) seedlings.

Methods A hydroponic experiment was conducted with six Cd stress treatments (0, 2.5, 5.0, 10.0, 20.0, 50.0 μmol/L), and the growth indexes, cadmium and mineral element (calcium, magnesium, iron, zinc, potassium) uptake, photosynthetic physiology, and antioxidant enzyme activity responses of capsicum seedlings under different concentrations of Cd stress were analyzed.

Results When Cd stress concentration was low, the growth indexes and mineral content of capsicum seedlings increased obviously; but with the increase of Cd stress concentration (≥10.0 μmol/L), the growth of capsicum was significantly inhibited. Under Cd stress, hydrogen peroxide and superoxide anion accumulated in the root tip tissues, causing oxidative damage to the root tip; the net photosynthetic rate, transpiration rate, stomatal conductance, and inter-cellular CO₂ concentration showed a fluctuating downward trend, and reached the lowest value under 50.0 μmol/L Cd stress concentration, which decreased by 17.62%, 52.60%, 50.00% and 20.38% compared with the control; the chlorophyll content gradually decreased by 5.14%-39.62% compared with the control. Under 10.0 μmol/L Cd stress, the catalase (CAT) activity was significantly increased by 72.21% compared with the control; under 20.0 and 50.0 μmol/L Cd stress, superoxide dismutase (SOD) and peroxidase (POD) activities were significantly increased, while CAT activity was significantly decreased. With the increase of Cd stress concentration (except 2.5 μmol/L), the soluble protein content gradually decreased, with a decrease of 8.16%-44.18%. With the increase of Cd stress concentration, the contents of Cd in roots, stems and leaves increased gradually and were mainly enriched in roots, but the concentration factor decreased gradually.

Conclusion Cd stress has a dose effect on the growth, development and mineral element uptake of capsicum seedlings overall performance of “promote under low stress, inhibit under high stress”. Capsicum seedlings respond to Cd stress by regulating antioxidant enzymes and osmoregulatory substances and sequester most of the Cd in the roots, providing them with some regulatory and detoxification capacity in response to Cd stress.