Studies On The Physiological Effects Of Lead Stress On Rice Growth And The Characteristics Of Uptake And Accumulation Of Lead By Rice Plant

Heavy metal pollution is one of the most concerned environmental problems inthe world, in which the pollution caused by lead is the main one due to the widesourses of lead emitted to the environment. The lead pollution is increasingly seriousin soil-plant-environment system, and it has become one of the main obstacles forthe food safety of china's rice production. However, the knowledges about thedistribution, transformation and accumulation of lead in the rice plant are quitelimited because of the complexity of the processes and mechanisms involved in it.The physiological effects of lead on the rice plant and its uptake andaccumulation by two rice cultivars, which were Azucena and IR1552, were studied,and the major results obtained were summarized as follows:1. While compared with the growth indicators, lead impact on morphologicalindicators of Azucena was not obvious, and the resistance of Azucena to lead stresswas stronger than that of IR1552. The results also showed that that biomassindicators was more sensitive to lead poisoning. Among the different parts of therice plant, root was more sensitive than the aerial part under lead stress, whichshowed that the root weight was much more sensietive to lead stress than that of theaboveground biomass, plant height, and the root length. Photosynthetic rate of thetwo cultivars decreased when the lead concentration increased2. The variation range of the relative activity of SOD and CAT were differentbetween the two cultivars. The MDA content in Azucena leaf was positivelycorrelated with the lead concentration of the treatment, whereas the correlation ofwhich in IR1552 leaf was much more significant. The CAT activity increased withthe lead concentration increased, indicating that the enzyme activities of SOD andPOD in the leaves of the two rice cultivars were negatively correlated with MDAcontent, representing that the content of MDA in the leaf coule induce the decline ofthe activities of SOD and POD.3. The lower concentration of lead had some benefical effects to the formationof iron plaque, while the higer concentration of lead had the reverse effects. Most of the uptake lead was accumulated in the iron plaque of the roots, and less wasabsorbed into the roots and then transported to the aerial parts of the rice plant. Thecorrelation analysis among the content of lead in the rice roots with the additionamount of Pb showed that the iron plaque on the root surface could not significantlyinhibit the uptake and transport of lead by rice plant. Based on the different rates ofPb transportation from roots to shoots, the lower one of that of the rice cultivar couldbe considered the convenient cultvar to be choose under lead stress.