Nanoceria exposure to kidney beans (Phaseolus vulgaris ): Implications on plant physiology, nutrition and their transfer to next trophic level

Previous studies investigating the effects of cerium oxide nanoparticles (nanoceria, nCeO2) on plants have primarily focused on the physiological and biochemical changes at early growth stages. Comprehensive information on the effects of nCeO2 through the entire life cycle of plants and the nutritional quality of the edible tissues is limited. No studies have been reported on the interactions between nCeO2 and common beans (Phaseolus vulgaris). This research was performed to comprehend the impact of nCeO 2 on plant health, defense mechanisms, yield and nutritional quality of P. vulgaris var. red hawk kidney beans, and further transfer of nCeO2 to a primary consumer in a terrestrial food chain. The broad scope of this research was divided into four major phases. Phase I was focused towards the mechanism of uptake and toxicity in a hydroponic system. Phase II evaluated soil organic matter as a factor towards the impact of nCeO2 on plant physiology, metabolism, productivity, and bean nutritional quality. Phase III involved exploring the molecular mechanisms responsible for modulation of bean nutritional quality by nCeO 2. In Phase IV, the possible trophic transfer of nCeO 2 from the plant to a primary consumer was examined. To accomplish the goals of Phase I, plants were exposed to nCeO2 suspensions (0, 62.5, 125, 250 and 500 mg/L) in hydroponics and analyzed for Ce uptake and translocation after 1, 7, and 15 days of exposure, using ICP-OES. In Phase II, the plants were grown in soils varying in their organic matter content (low organic matter soil: 4%, LOMS and organic matter enriched soil: 10%, OMES), amended with 0 to 500 mg/kg nCeO 2 through their complete life cycle. Plant tissues were analyzed for Ce accumulation, leaf area, photosynthetic pigments and metabolic activities like net photosynthesis, transpiration, and stomatal conductance. In Phase III, proteomic analyses performed using LC MS/MS tandem spectrometry on the beans harvested upon nCeO2 exposure revealed that at 125 and 250 mg/kg, nCeO2 induced two proteins, defensin and purple acid phosphatase, responsible for stress response and metabolism, respectively. However, the number of downregulated proteins increased, with increasing nCeO2 exposure concentration. Phase IV of this dissertation was accomplished by infesting plants exposed to 1000 and 2000 mg/kg nCeO2 with Mexican bean beetles (Epilachna varivestis). The beetles were allowed to grow through their entire life cycle, feeding on nCeO2 exposed plants. Then they were analyzed for Ce accumulation at the various stages of development. Beetles were shown to accumulate Ce in tissues, depending on the exposure concentration, and their food assimilation habits at different developmental stages. (Abstract shortened by UMI.