The Study Of The Injury Of The Heavy Metal Lead (Pb) On Longan

The Pb contents of soil,water and fruit in longan orchard near by rubbish landfill site were investigated.The one-age longan seedlings were used to study under Pb stressed,and the results were as followed:1.Green-revertible yellow symptom was found in the old leave of longan seedlings under Pb stressed.Epidermal structure in leaves was severely destroyed by heavy metal stress.The Pb concentration below 400mg/L improved the growth of longan seedlings, while the growth was inhibited under higher concentration stress.Water metabolism in longan seedlings disordered under Pb stressed,and the ability of absorbing water declined obviously.The influence degree of water content in longan organs is:leave＞stem＞root.The Pb content in longan seedling increased with the increasing of Pb stressed concentration.The ability of absorbing Pb in longan organ is:root＞stem＞leave.2.The closer to rubbish landfill site,the fruit quality dropped more severely,and the total soluble sugar content was the most sensitivity to heavy metal pollution.The heavy metal Pb was much abundant in the orchard around rubbish landfill site.The closer to rubbish landfill site,the pollution was more severely.The Pb content in longan fruit from polluted orchard was remarkably over standard.The bio-accumulation part in the plant was different.The bio-accumulation ability of fruit is higher than that in leaves.3.The contents of chlorophyll a,chlorophyll b and chlorophyll descended due to the increasing of Pb content.The carotenoid content was high under low Pb concentration stress,and the content dropped gradually under higher Pb concentration.The Pb stress led to Fo value raise,and the remarkable decrease of Fm,Fv and Fv / Fm value.The increase of Pb treatment concentration resulted in the decrease of net photosynthetic rate and its daily changing range.The Cs and transpiration rate raised first and then decline with the increasing of PAR under Pb treated.4.With the Pb concentration increasing,the production rate of H₂O₂ and O₂·^- increased,the SOD activity,cell membrane permeability,MDA content and free proline content ascended,the POD activity and soluble protein content descended.The activity of CAT and APX increased and then decreased with Pb concentration increasing.It was also found that CAT and POD was more sensitive than SOD.The isozyme expression of POD,PPO,SOD and APX in longan seedlings changed with different degrees under Pb stressed.