Date of Award

2014-01-01

Degree Name

Doctor of Philosophy

Department

Environmental Science and Engineering

Advisor(s)

Jorge Gardea-Torresdey

Abstract

Nanotechnology is increasingly attracting attention not only for its variety of applications in modern life, but for the potential negative effects that nanomaterials (NMs) can cause in the environment and human health. Studies have shown varied effects of engineered nanoparticles (ENPs) on plants; however, most of these studies focused on the interaction of NPs with plants at root level. The increasing production and use of NPs have also increased the atmospheric amounts of NPs, which could be taken up by plants through their leaves. Cucumbers (Cucumis sativus L.) are broad leaf plants commonly grown both commercially and in home vegetable gardens that can be easily impacted by atmospheric NPs. However, there is limited information about the potential effects of these atmospheric NPs on cucumber. This research was aimed to determine (I) the possible uptake and translocation of cerium (Ce) by cucumber plants exposed to nCeO2 (cerium dioxide nanoparticles, nanoceria) through the foliage, (II) the impacts of the NPs on physiological parameters of the plants and the effects on the nutritional value and quality of the fruits, and (III) the effects of seven copper compounds/nanoparticles applied to the growth medium of lettuce (Lactuca sativa) and alfalfa (Medicago sativa). For aim I, 15 day-old hydroponically grown cucumber plants were exposed to nCeO2, either as powder at 0.98 and 2.94 g/m3 or suspensions at 20, 40, 80, 160, 320 mg/l. Ce uptake was analyzed by using inductively coupled plasma-optical emission spectroscopy (ICP-OES) and transmission electron microscope (TEM). The activity of three stress enzymes was measured by UV/Vis. Ce was detected in all cucumber tissues and TEM images showed the presence of Ce in roots. Results suggested nCeO2 penetrated plants through leaves and moved to other plant parts. The biochemical assays showed nCeO2 also modified stress enzyme activities. For aim II, 15 day-old soil grown cucumber plants were foliar treated, separately, with 50, 100, 200 mg/L of nCeO2, nCuO and the respective bulk material suspensions. Photosynthetic rate (Pn), stomatal conductance (gs), and transpiration (E) of cucumber leaves were measured with a portable gas exchange system. Nutritional elements and Ce/Cu uptake were determined by ICP-OES. Quality of cucumber fruits was evaluated after harvest. Results showed that cucumber absorbed Ce and Cu through foliar applied nCeO2 and nCuO and translocate them to new leaves and fruits. Photosynthetic and transpiration rates were only affected in new leaves. None of the treatment significantly affected cucumber, yield, length, and diameter of fruits. However, both nCeO2 and nCuO significantly reduced the firmness of the fruit. Mineral element determination in fruit showed that Zn decreased by 25% with 200 mg/L of both nCeO2 and bulk CeO2 and in fruit Mo decreased by 51% and 44% with both nCuO and bulk CuO at 200 mg/L, respectively. For the aim III, 15 day-old hydroponically grown lettuce and alfalfa were exposed to 0, 5, 10, and 20 mg/L nCu, bulk Cu, nCuO, bulk CuO, Cu(OH)2 (CuPRO 2005, Kocide 3000), and CuCl2. The concentration of Cu, macro and microelements in plants were measured by using ICP-OES. The size of the plants and the activity of catalase and ascorbate peroxidase were also determined. Results showed that all Cu NPs/compounds reduced the root length by 49% in both plant species. Under all treatments, Cu, P, and S were increased (>100%, >50%, and >20%, respectively) in alfalfa shoots; while P and Fe were decreased (>50% and >50%, respectively) in lettuce shoot. In addition, catalase activity was reduced in alfalfa (root and shoot) and ascorbate peroxidase activity was increased in roots of both plant species. Our findings show that increasing concentration of atmospheric nCeO2 can affect the nutritional value of crop plants with unknown consequences for the food chain. In addition Cu NPs/compounds could impact the growth of plants and altered the quality of crops as well. These results will help to understand the eco-toxicity of NPs in food crops.

Language

en

Provenance

Received from ProQuest

File Size

97 pages

File Format

application/pdf

Rights Holder

Jie Hong

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