Effects of Cd stress on Cd accumulation, physiological response and ultrastructure of Lolium multiflorum

The pot experiments were conducted to investigate effects of cadmium(Cd) stress on cadmium accumulation, physiological response and ultrastructure of Lolium multiflorum under different concentrations of Cd stress. The results showed that aboveground Cd content was less than the critical value (100 mg·kg-1) and underground Cd contents and the translocation factor was less than 1 which suggest that L. multiflorum is not Cd hyperaccumulator. The low concentrations (50 mg·kg-1) Cd stress stimulated the chlorophyll synthesis whereas high concentration Cd stress inhibited the chlorophyll synthesis. With Cd concentration increasing, the initial fluorescence (F0) gradually increased, the maximum fluorescence (Fm) firstly increased and then decreased, while photochemical efficiency of PSⅡ(Fv/Fm) and potential photochemical efficiency of PSⅡ (Fv/F0) gradually decreased, quantum yield (PSⅡ), electron transfer efficiency (ETR), photochemical quenching coefficient (qP), non photochemical quenching coefficient (qN) firstly increased and then decreased. The indices of physiological had different performance. With Cd concentration increasing, CAT activities firstly decreased and then increased and decreased again, however, superoxide dismutase activities firstly increased and then decreased and proline contents gradually increased. Compared with the control, POD activities increased, however, MDA contents had no significant increase which suggest that the leaves of L. multiflorum did not have high degree membrane lipid peroxidation. The high Cd concentration (300 mg·kg-1) injury ultrastructure of L. multiflorum which made part of the chloroplast grana lamellae hollowed, granum lamella dissoluted, mitochondrial cristae structure reduced and osmiophilic particles increased. This study indicated that L. multiflorum had stronger accumulated ability and physiological resistance to Cd stress and could be used in remidiation for Cd contaminated soil.