Thesis (M.Sc.)--Chulalongkorn University, 2011

The present study investigated the effects of nanoparticles of titanium dioxide (nano-TiO₂) and zinc oxide (nano-ZnO) on rice (Oryza sativa L.) seed germination and root development. In this work, seeds of the rice cultivar Pathum Thani 1 were used and four different parameters: a) seed germination percentage, b) root length, c) root number and d) relative root growth were analyzed after treating rice seeds and seedling with different concentrations of nanoparticles. The results show that there was no reduction in the percentage of seed germination for both ZnO and TiO₂ nanoparticles. Also, whilst nano-TiO₂ had no effects on root length, root number and relative root growth of rice seedlings, nano-ZnO was observed to cause significant reduction of both root length and number. For the relative root growth measurements, the nano-ZnO exposure also caused decrease in root elongation even at low concentration as 10 mg/L nano-ZnO. Further study on the effects of the nanoparticles on anatomical structure of root treated with nano-ZnO was performed. Globules were observed in the cortical cell treated with nano-ZnO, leading to the conclusion that the globules were formed specifically to nano-ZnO. The fluids within the globules were not analyzed in this study, but it might either contain nano-ZnO, zinc ion, or possibly other substances produced by plant cells. Further studies on the development of the globules and their fluid compositions are recommended. Overall, this study shows that direct exposure to some types of nanoparticles i.e. nano-ZnO can cause significant toxicity on root development of economically important rice plants. This detrimental effect of nano-ZnO should be of great concern for both plant production and the ecosystems, and emphasize the need for responsible treatment and disposal of wastes containing nanoparticles so that they are not released into the unprotected environment.