Engineered nanoparticles (ENPs) are materials with a size of < 100 nm in at least one dimension. ENPs are used in medicine, agriculture, and construction; and, in consumer goods such as sunscreens, clothing, and electronics. ENPs generally fall into two classes: carbon based or inorganics based on metals (e.g., Ag, Zn) and metal oxides (e.g., Fe2O3, TiO2). ENPs display unique physiochemical properties due to their small size and large surface area-to-volume ratio. Here I report on the effects of a 4 ug/mL silver quantum dot (Ag QD) and 4 ug/mL single walled carbon nanotube (CNT) on gas exchange in Arabidopsis thaliana. Plants were grown for 30 days in Petri dish plates in sterile media. The method of growth used was developed so RNA could be extracted after 14 days of growth. I measured gas exchange with a LiCor 6400 at 14, 22 and 30 days. I measured gas exchange at growth light (150 umol/m2/s) and saturating light (500 umol/m2/s). I also obtained light saturation and CO2 saturation (ACi) data. I used published Excel Solver functions to analyze light and ACi curves. A secondary goal of the experiment was to establish standard screening protocols for ENP effects on plants.
Results/Conclusions
At the concentrations tested, neither CNTs nor Ag QDs were “toxic”. However, CNTs marginally affected photosynthetic capacity while Ag QDs very significantly reduced photosynthetic capacity. Using this growth method, the best time frame for measuring photosynthetic capacity was 14 and 22 days. This validates the system for extraction of RNA at day 14. Quantum use efficiency was only significantly reduced by Ag QDs. ACi analysis indicates that Ag QDs limit both rubisco and TPU, but not RuBP. In CNT grown plants, a gene that plays a key regulatory role in balancing stress responses and auxin signaling was very significantly affected. In Ag QD grown plants, 26 genes were significantly differently regulated, with most of these genes associated with environmental stress responses and signal transduction. The most dramatically impacted genes in Ag QD plants were those that code for peroxidase. The results indicate that plants exposed to CNTs will be mildly stressed and have small reductions in growth; on the other hand, plants exposed to Ag QDs will experience significant stress and growth reductions. These results will be discussed in light of the highly variable responses of plants to ENPs that are reported in the literature.