Effects of Pb stress on germination and physiological metabolism of lettuce seeds.

Lead is one of the most widespread and dangerous heavy metals in the environment.It is toxic to seed germination and seedling growth.In order to explore the effects of lead on seed germination and physiological metabolism,lettuce variety Sunwang NO.1 was taken as material to investigate germination rate,germination potential,germination index,vigor index and the changes of malonaldehyde content(MDA),superoxide dismutase(SOD) activity,peroxidase(POD) activity,catalase(CAT) activity,and relative conductivity under Pb stress by solution culture.The results showed that 0.6 mmol/L Pb could promote germination rate,however,as Pb concentration increased from 1.2 mmol/L to 6.0 mmol/L,the germination rate was decreased.The germination potential,germination index,vigor index exhibited the same change trends as germination rate being promoted at lower Pb concentration and being inhibited at higher Pb concentration.In addition,MDA content,relative conductivity and activities of SOD and POD in plumule were improved gradually with the increase of Pb concentration,but 3.6 mmol/L Pb depressed SOD activity.The activities of CAT droped at lower Pb concentrations and rose at higher Pb concentrations.The results indicated that oxidative stress contributed to the inhibion of seed germination and seedling growth of lettuce by Pb.