Location: Children's Nutrition Research CenterTitle: Effects of nano-TiO2 on the agronomically-relevant Rhizobium-legume symbiosis Author
Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/10/2013
Publication Date: 1/1/2014
Citation: Fan, R., Huang, Y.C., Grusak, M.A., Huang, C.P., Sherrier, D.J. 2014. Effects of nano-TiO2 on the agronomically-relevant Rhizobium-legume symbiosis. Science of the Total Environment. 466-467:503-512. Interpretive Summary: Legume plants, like bean, pea, and soybean, can meet part of their nitrogen requirements by capturing atmospheric nitrogen through an association in their roots with a beneficial bacterium called Rhizobium. This occurs in a structure called the root nodule. Our goal is to ensure that legume plants are as successful as possible in making this association with Rhizobium, because when legume plants are successful, farmers can grow them with less nitrogen fertilizer. This keeps their production costs down, food prices are lower, and it is good for the environment. In this study, we assessed whether man-made nano-particles, in the form of nano-titanium oxide (nano-TiO2), might impact root growth or root nodule development in pea plants. Nano-TiO2 particles are extremely small in size, they are used by industry as a whitening agent in various household products, and subsequently they are frequently dispersed into the environment (including agricultural soils). We grew pea plants, the Rhizobium bacterium, or the two together, and exposed them to varying concentrations of nano-TiO2 or control conditions. There were no direct effects of nano-TiO2 on the plant roots, but changes were seen in the appearance of the bacterium and in the development of the root nodules. These results suggest that nano-TiO2 contamination of the environment may be detrimental to the legume-Rhizobium association, and thus should be monitored to ensure that legume productivity is not diminished.
Technical Abstract: The impact of nano-TiO2 on Rhizobium-legume symbiosis was studied using garden peas and the compatible bacterial partner Rhizobium leguminosarum bv. viciae 3841. Exposure to nano-TiO2 did not affect the germination of peas grown aseptically, nor did it impact the gross root structure. However, nano-TiO2 exposure did impact plant development by decreasing the number of secondary lateral roots. Cultured Rhizobium leguminosarum bv. viciae 3841 was also impacted by exposure to nano-TiO2, resulting in morphological changes to the bacterial cells. Moreover, the interaction between these two organisms was disrupted by nano-TiO2 exposure, such that root nodule development and the subsequent onset of nitrogen fixation were delayed. Further, the polysaccharide composition of the walls of infected cells of nodules was altered, suggesting that the exposure induced a systemic response in host plants. Therefore, nano-TiO2 contamination in the environment is potentially hazardous to the Rhizobium-legume symbiosis system.