Effects of arbuscular mycorrhizal fungi inoculation on the photosynthetic pigment contents, anti-oxidation capacity and membrane lipid peroxidation of Elsholtzia splendens leaves under copper stress

Arbuscular mycorrhizal fungi ( AMF ) , which engage in a mutualistic symbiosis with the roots of most plant species, have been well studied for their ability to alleviate heavy metal stress, including that of copper ( Cu) , in plants. Most mycorrhizal studies have focused on AMF effects on host plant nutrient uptake. However, few studies have investigated plant physiological responses during plant-microbe interactions, which are necessary to understand the efficiency of the phytoremediation of heavy metal pollution. Elsholtzia splendens, a widely distributed Cu-tolerant plant, is usually found in the Cu mining areas of southern China and is colonized by symbiotic AMF. This study examines the effects of AMF on the physiological responses of E. splendens leaves under Cu stress. A controlled pot experiment was performed to investigate the effects of AMF inoculations and Cu additions on E. splendens leaves' photosynthetic pigment contents, anti-oxidation enzymatic activities, antioxidant contents and lipid peroxidation. The plants, which were grown on a mixture of sterilized soil and sand, were inoculated with AMF (non-inoculated plants were controls), with or without the addition of Cu (1000 mg/kg and 0 mg/kg, respectively) . The results showed that AMF could well colonize the roots of E. splendens under both Cu treatments. The plant root biomass, stem biomass, leaf biomass, inflorescence biomass and total biomass of E. splendens under Cu stress were lower than in the control. Inoculations with AMF significantly increased the plant root biomass, stem biomass, leaf biomass, inflorescence biomass and total biomass of E. splendens under Cu stress by 36. 1%, 138. 9%, 47.3%, 68. 4% and 79. 7%, respectively, and significantly decreased the root shoot ratio by 26. 3%, indicating an alleviating effect of Cu inhibition on E. splendens growth. Compared with the control, the chlorophyll a ( Chl a ) and chlorophyll b ( Chl b) contents, Chl a+b content [ Chl ( a+b) ] , carotenoid content and chlorophyll a/b ratio ( Chl a/b) under Cu stress significantly decreased by 56. 2%, 52. 6%, 55. 1%, 49. 8% and 7. 5%, respectively. Additionally, the superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), catalase (CAT), glutathione (GSH) and ascorbic acid ( AsA) contents in the leaves of E. splendens under Cu stress significantly decreased by 44.8%, 45.0%, 61.0%, 43.7%, 49.2% and 31.1%, respectively, while the membrane relative permeability (MRP) and malondialdehyd