Toxicological Effects And Micromechanism Of Heavy Metals Pollution On Wheat

Soil heavy metals pollution has become one of main potential hazards of food security. Nonetheless, there were less research on eco-toxicity and toxic mechanisms of mixed heavy metals with moderate and low concentration. Dish culture and pot culture experiments were carried out to study the toxicological effects of Cu, Cd, Pb, Zn and their binary mixtures on wheat. Damage of heavy metals on wheat seedlings were observed microscopically by Transmission Electron Microscopy. Responses of soil enzyme to heavy metal pollution and heavy metals enrichment characteristic of wheat were also studied during wheat upgrowth polluted by the heavy metals. The major conclusions were listed as follows:(1) Effect of binary heavy metal interaction on physiological characteristics of wheat seedling and heavy metals enrichment characteristics were systematically studied. The results showed that binary heavy metal interaction posed antagonism towards all physiological characteristics index to different degrees. And it affects root elongation the most significantly (coefficient of variation was the biggest). The actions of each heavy metal element and their binary mixtures on Cu, Cd, Zn enrichment were significant. And extremely significant enrichment of Pb was acquired due to the actions mentioned above. The conclusion provided evidence for prediction of soil heavy metal pollution..(2) Damage mechanism of heavy metals and their interaction on wheat cells and metals deposition state were studied by observation of ultrastructure of root-tip and leaves cell of wheat seedling using TEM. The observation indicated that the responses of different organelles to heavy metals and their interaction were different. Adsorption of wall and storage of vacuole and organelles could mitigate damage of wheat cells by heavy metals. Some organelles, such as mitochondria , nucleolus and chloroplast, would be damaged by heavy metals with high concentration that exceeding resistance range of wheat cell. The result of microscopic observation was in accordance with the result of physico-chemical analysis. The whole process that complete damage of wheat seedling cells stressed by some binary mixtures of heavy metals was experimentally observed, which established a theoretical foundation of further understanding of micromechanism of mixed heavy metals damage to wheat were .(3) Response of sucrase, urease and catalase activity in both rhizosphere and non-rhizosphere of wheat root to heavy metals and their interactions were tested continually by pot culture. The testing results indicated that sucrase and urease activity in both rhizosphere and non-rhizosphere were inhibited as stressed by heavy metals totally and the inhibitions were related to the concentration of heavy metals while catalase activity was more correlated with wheat growth. Generally sucrase, urease and catalase activity in rhizosphere were bigger than that in non-rhizosphere and the order of rhizosphere effect promoting soil enzyme was sucrase activity>catalase activity> urease activity.(4) Orthogonal experiments was carried out systematically to study mixed heavy metals enrichment in wheat during wheat growth. The results showed that heavy metals in roots, stems and leaves were more than that in glumes and seeds as stressed by heavy metal during the wheat growth and the enrichment amount was related to the heavy metal concentration. The heavy metal enrichment varied in different growth stages of different part of wheat stressed by mixed heavy metals. Generally, the heavy metals enrichment in early growth stage is bigger than that in later growth stage. Most of the enrichment amount of heavy metals in wheat were significantly correlated to the concentration of the heavymetal and the correlation decreased with wheat growth.(5) Cd, Pb, Zn concentration in seed exceeded sanitary standards for foods as stressed by single heavy metal. The ranges of heavy metals enrichment amount were enlarged by interaction of mixed heavy metals to some extent. Each heavy metal exceeded the standards to some degree. Zn had the most ratio of exceeding the standards. And Cd had the most times of exceeding the standards. It's concluded that Yan-nong 19 is easy to be contaminated as planting in the heavy metals polluting areas...