Toxicities of DDE and cadmium towards the wheat Triticum aestivum and their cleanup by the fungus Pleurotus pulmonarius.

摘要

Soil pollutants affect the yield of crops, and if bioaccumulated, the contaminated crop poses health hazard. Wheat Triticum aestivum is a major global food crop. Dichlorodiphenyldichloroethylene (DDE), the persistent metabolite of a synthetic but banned organochlorine pesticide DDT, and cadmium, a toxic heavy metal, are common environmental pollutants in agricultural soils. The present study was undertaken to systematically assess the toxicities of DDE and cadmium on T. aestivum. Besides, a feasibility study on using a white rot fungus Pleurotus pulmonarius in cleanup of artificially contaminated soils was carried out and assessed.; In terms of acute phytotoxicity on seed germination and growth of germlings performed with a standardized bioassay, soil, in contrast to filter paper as matrix, showed sorption and reduced bioavailability which in turn, lowered the cadmium toxicity on T. aestivum. DDE up to 10 mg/kg did not exert acute phytotoxicity. But genotoxicity in terms of DNA breakage measured by single cell gel electrophoresis was detected for both cadmium (ranging from 1 to 50 mg/kg) and DDE (ranging from 0.3 to 10 mg/kg) after 3-day treatment. Root was the major organ for accumulating the pollutants but shoot suffered severe genotoxicities. Besides, differential expression of genes phytochelatin synthase (PCS) and metallothionein (MT) detected by reverse transcription polymerase chain reaction (RT PCR) revealed that both cadmium and DDE enhanced the expression of these genes in both filter paper and soil as matrices. Longer exposure, however, did not maintain the enhanced expression levels of PCS and MT.; For chronic exposure up to the flowering and grain harvesting stages in pot plant system, tolerance towards these two pollutants was found; all seedlings survived at low contamination levels and up to 10 mg DDE/kg and 200 mg Cd/kg. The treated plants showed normal elongation rates but retarded growth at 2 and 4 months at extremely high concentrations of cadmium. At soil contamination levels exceeding the acceptable limits, cadmium (>1 mg/kg) retarded flowering development and reduced grain yield (seed mass) while DDE (>0.5 mg/kg) decreased grain rate (percentage of mature grains per ear). (Abstract shortened by UMI.)