Location: Children's Nutrition Research CenterTitle: Effects of nano-ZnO on the agronomically relevant Rhizobium-legume symbiosis
|Huang, Yu - University Of Delaware|
|Fan, Ruimei - University Of Delaware|
|Sherrier, Janine - University Of Delaware|
|Huang, C - University Of Delaware|
Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2014
Publication Date: 11/1/2014
Citation: Huang, Y.C., Fan, R., Grusak, M.A., Sherrier, J.D., Huang, C.P. 2014. Effects of nano-ZnO on the agronomically relevant Rhizobium-legume symbiosis. Science of the Total Environment. 497-498:78-90.
Interpretive Summary: Legume plants, like bean, pea, and soybean, can meet part of their nitrogen requirements by absorbing atmospheric nitrogen and converting it to a useful nitrogen form. This occurs through an association in their roots with a beneficial bacterium called Rhizobium, in a structure called the root nodule. Our goal is to ensure that legume plants are as successful as possible in making a functional association with Rhizobium, because when successful, farmers can grow their legume crops 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-zinc oxide, might impact root growth or root nodule development in pea plants. Nano-zinc oxide particles are extremely small in size, they are used in various commercial and personal care 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-zinc oxide or control conditions. Nano-zinc oxide treatments caused a reduction in lateral root numbers and leaf area in pea plants, as well as changes in the appearance of the bacterium and in the development of the root nodules. These results suggest that nano-zinc oxide 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-ZnO (nZnO) on Rhizobium-legume symbiosis was studied with garden pea and its compatible bacterial partner Rhizobium leguminosarum bv. viciae 3841. Exposure of peas to nZnO had no impact on germination, but significantly affected root length. Chronic exposure of plant to nZnO impacted its development by decreasing the number of the first- and the second-order lateral roots, stem length, leaf surface area, and nutrient solution uptake. The effect of nZnO dissolution on phytotoxicity was also examined. Results showed that Zn2+ had negative impact on plant development. Exposure of Rhizobium leguminosarum bv. viciae 3841 to nZnO brought about morphological changes by rendering the microbial cells toward round shape and damaging the bacterial surface. Furthermore, the presence of nZnO in the rhizosphere affected root nodulation, delayed the onset of nitrogen fixation, and caused early senescence of nodules. Attachment of nanoparticles on the root surface, formation of oxygen reactive species (ORS) due to photocatalysis, dissolution of Zn2+, and pH buffering capacity in the rhizosphere are important factors affecting the phytotocity of nZnO. Hence, the presence of nZnO in the environment is potentially hazardous to the Rhizobium-legume symbiosis system.