Arsenic and nutrient absorption characteristics and antioxidant response in different leaves of two ryegrass (Lolium perenne) species under arsenic stress

Arsenic (As), a heavy metal element, causes soil environmental concerns in many parts of the world, and ryegrass has been considered as an effective plant species for bioremediation of heavy metal pollution including As. This study was designed to investigate As content, nutrient absorption and antioxidant enzyme activity associated with As tolerance in the mature leaves, expanded leaves and emerging leaves of perennial ryegrass (Lolium perenne) and annual ryegrass (Lolium multiflorum) under 100 mg.kg-1 As treatment. The contents of As, calcium (Ca), magnesium (Mg), manganese (Mn) in the leaves of both ryegrass species were greatest in the mature leaves and least in the emerging leaves. The nitrogen (N), phosphorus (P), potassium (K) contents of both ryegrass species were greatest in the emerging leaves and least in the mature leaves. The As treatment reduced biomass more in the mature leaves and expanded leaves relative to the emerging leaves for annual ryegrass and reduced more in emerging leaves relative to the mature and expanded leaves for perennial ryegrass. Perennial ryegrass had higher As content than annual ryegrass in all three kinds of leaves. The As treatment increased hydrogen peroxide (H2O2) in expanded leaves of two ryegrass species, relative to the control. The As treatment increased the ascorbate peroxidase (APX) activity in the expanded leaves of perennial ryegrass and the mature leaves of annual ryegrass, the catalase (CAT) activity in the mature and expanded leaves of perennial ryegrass and the emerging leaves of annual ryegrass, relative to the control. The As treatment reduced peroxidase (POD) activity in all three kinds of leaves of annual ryegrass and superoxide dismutase (SOD) activity in expanded leaves of perennial ryegrass, relative to the control. The results of this study suggest that As tolerance may vary among different ages of leaf and reactive oxygen species (ROS) and antioxidant enzyme activity may be associated with As tolerance in the ryegrass.