The Physiological Effects Of Cadmium Stress On Lolium Perenne L. And Effect Of Exogenous Melatonin To Mitigation

In recent years,with the accelerated process of industrialization and urbanization,different degrees of Cd pollutions are existing in the urban soil here and there,and urban ground cover ornamental plants were grown in the Cd contaminated soil inevitably.Therefore,It is very meaningful to define the effects of Cd stress on the growth of urban ground cover plant and explore the way to alleviate the Cd toxicity.In this study,the effects of cadmium stress(10,25,50,75,100mg/L)on the germination rate,seedling growth and antioxidant system were studied in perennial ryegrass(Lolium perenne L.),furthermore,the regulation mechanism of regulation of different concentrations of exogenous melatonin(50,100,200,400umol/L)on perennial ryegrass under cadmium stress were also investigated.The main results are as follows:(1)The experimental results showed that 10mg/L cadmium treatment had no significant effect on the germination rate and germination energy of perennial ryegrass comparison with control,but with the increase of cadmium stress,the germination rate and germination potential decreased gradually with the increase of cadmium stress.All concentrations of cadmium significantly inhibited the growth of seedling root length,shoot height,growth of lateral root and biomass accumulation,and the inhibition effect was more significant with the increase of cadmium stress.Comparison with control,the relative conductivity and malondialdehyde content in shoots and roots of the seedlings increased significantly with the increase of cadmium concentration,and the activity of SOD,POD and CAT enzymes was activated by cadmium treatment.When the concentration of cadmium was higher than 50mg/L,the activity of SOD and CAT enzymes decreased rapidly,and the antioxidant clearance system was destroyed,resulting in membrane lipid peroxidation.In result,growth of perennial ryegrass seedlings are inhibited.(2)In the pot experiment,comparison with control,the 75mg/kg cadmium stress of75mg/kg significantly reduced the chlorophyll content and net photosynthetic rate in theshoots,inhibited the activity of antioxidant enzymes in shoots and roots,enhanced the accumulation of active oxygen,and resulted in a significant increase in the content of cadmium in shoots and roots,thus causing poison to perennial ryegrass.Spraying different concentrations of exogenous melatonin(50,100,200,400umol/L)could effectively alleviate the stress damage to perennial ryegrass.When the concentration of melatonin was200umol/L,the effect was most significant.Compared with the cadmium stress,melatonin in 200umol/L could increase the biomass of shoot and root,increase the net photosynthetic rate and chlorophyll content,reduce the oxidative damage of cell membrane,increase the activity of SOD,POD,CAT,GR and APXenzymes,increase the content of ASA and GSH,increase the synthesis of PC in the root and decrease the content of cadmium in leaves.In summary,application of the suitable concentration of exogenous melatonin could increase the photosynthesis,enhance the activity of antioxidant enzymes,reduce oxidative damage,enhance the chelation of cadmium ions in the roots and PC,and reduce the transfer of cadmium from roots to the shoots,thus effectively alleviating the toxicity of cadmium to perennial ryegrass.