| A hydroponic experiment was carried out to investigate the effect of different Pb levels on photosynthetic characteristics and the activity of antioxidant enzymes in wheat seedlings,which established the link between crop growth status and some related index, simultaneously in the meantime discussing the effect on wheat seedings under lead stress by using a new approach-protemics,it can provide the mechanism for heavy metal to poison the plant. The experimental results are as follows:1.By the measurement of wheat leaf of net photosynthetic rate, transpiration rate, stomatal conductance, intercellular CO2 and SPAD value, in order to discuss the photosynthesis and the influence of the chlorophyll content of lead stress on wheat seedling.The results showed that appropriate Pb concentration (50,100 mg/L) promoted the growth of seedlings and roots,but when the concentration exceed a certain range (200,300 mg/L) , the growth of seedlings and roots were inhibited. The lead had a impact on wheat photosynthesis.The reason for the variation of photosynthesis is mainly caused by the stomata factors.In the experiments, the wheat plant height,the net photosynthetic rate (Pn) and the chlorophyll content were reached their peak value under 100mg/L treatment of Pb concentration,when Pb concentration reached 200 mg/L,it began to restrain the photosynthesis. The chlorophyll content and photosynthetic rate of change trend of the agreement with the lead concentration increased,SPAD value and photosynthetic rate rose.But to a certain value,the SPAD value no longer increased along with the lead concentration, photosynthetic rate also declined.2.By the measurement of catalase,peroxidase,superoxide dismutase and malondialdehyde, in order to study the effect of antioxidant enzymes activity and the stress on MDA content.The results showed that lead in low concentrations,the malondialdehyde content had no change,which has increased dramatically in high concentrations.The results showed that beyond a certain concentration,the plant cell membrane system damaged,and the damage rate was proportional to the lead concentration.in the early time,the activity of SOD, POD and CAT were activated, but the SOD activated the largest,POD and CAT change small scale,this is the reaction for the plant to resistant lead poison. But in high concentrations of lead stress,with the extension of time,the protective enzyme activity declined,the role of free radicals weakened gradually,which showed that antioxidant enzymes have a certain threshold to protect the system,the three kinds of protective enzyme protected cells from damaged by the lead stress of oxidation,which played an important role in the tolerance of wheat.3.?In order to study the effect of Pb stress on wheat blade protein obtained by TCA/acetone method, by the SDS-PAGE electrophoresis,it's found that some proteins were induced,some proteins increased in expression level,at the same time,some of the original protein disappeared. Lead completely inhibit the expression of 38.0kD molecular weight of protein (which disappeared in the lead concentrations,strip№. 1), and a new protein emerged, the molecular weight of which is 40kD,№. 3 and№. 4 were two kinds of proteins increased in expression level, the molecular weight were about 70kD. Thus the speculation, the disappearance of the protein may be a kind of photosynthesis protein, the emergence of new protein may be a heavy metal binding protein or heat shock protein. |
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