Effects of nanoparticles TiO₂and ZnO on growth and antioxidative responses of tomato and kidney bean

Abstract

Abstract

Although representative environmental pollution research institutions, the USEPA (US Environmental Protection Agency) and the OECD (Organization for Economic Cooperation and Development), have been doing research in many fields, research concerning the effects of nanoparticles on plants is still rare. In this study, I studied the effects of nanoparticles nano-TiO2, nano-ZnO on the tomato (Lycopersicon esculentum) and kidney bean (Phaseolus vulgaris) plants. The effects of two types of nanoparticles (nano-TiO2, nano-ZnO) on seed germination and root growth of two higher plant species, the tomato (Lycopersicon esculentum) and kidney bean (Phaseolus vulgaris) plants were investigated. The concentration range of the nanoparticles spanned from 0 to 5000 mg/L. In order to account for agglomeration and precipitation, a filter paper in a petri dish with distilled water (DW) was used. At all concentration levels, both nano-TiO2 and nano-ZnO did not significantly affect the seed germination of the tomato (Lycopersicon esculentum) and kidney bean (Phaseolus vulgaris) plants. However, significant inhibition of root length appeared in the treatment of nano-ZnO on the tomato (Lycopersicon esculentum) plant except at the highest concentration level of nano-ZnO. The same nanoparticle, nano-ZnO, significantly hampered the root length of the kidney bean (Phaseolus vulgaris) plant at high concentration levels (1000, 2500 and 5000 mg/L). The plant seeds uptake of the nanoparticles was also analyzed. In regard to nano-TiO2, after an exposure of 48 hours (mg/kg), it was observed that when the concentration of nano-TiO2 on the tomato (Lycopersicon esculentum) seeds increased, the uptake of nano-TiO2 by the tomato (Lycopersicon esculentum) seeds increased in a linear relationship although it was not significantly different. In addition, the kidney bean (Phaseolus vulgaris) seeds, at 100 mg/L, nano-TiO2 was not detected and at other higher nano-TiO2 concentrations it was detected. In the uptake analysis of nano-ZnO by the kidney bean (Phaseolus vulgaris) seeds, after an exposure of 48 hours (mg/kg), kidney bean (Phaseolus vulgaris) seeds also showed a significantly increased nano-ZnO uptake when the concentration of nano-ZnO on kidney bean (Phaseolus vulgaris) seeds increased. In addition to seeds, nanoparticle uptake by the tomato (Lycopersicon esculentum) and kidney bean (Phaseolus vulgaris) seedlings after an exposure of 15 days (mg/kg) was also measured. Although the tomato (Lycopersicon esculentum) seedlings didnt show significant differences with concentration levels of nano-TiO2, the kidney bean (Phaseolus vulgaris) seedlings showed significantly increased nano-TiO2 uptake at the highest concentration level (5000 mg/L). In nano-ZnO uptake by the tomato (Lycopersicon esculentum) and kidney bean (Phaseolus vulgaris) seedlings, after an exposure of 15 days (mg/kg), tomato (Lycopersicon esculentum) seedlings showed significantly increased nano-ZnO uptake at the highest level (5000 mg/L) and in the case of the kidney bean (Phaseolus vulgaris) seedlings, the uptake of nano-ZnO significantly increased with increased concentration levels. To determine the size of the nano-TiO2 and nano-ZnO in solution, after 14 days the hydrodynamic diameter of the nano-TiO2 and nano-ZnO uptake in a petri dish was measured. A FE-SEM (Field Emission Scanning Electron Microscope) was used to measure the diameter. For solutions which showed a particle diameter over 1000 nm, an Axio Zeiss Imager A1 with a differential interference contrast (DIC) microscope was used. In the case of nano-TiO2, the particles hydrodynamic diameter at the highest concentration significantly showed the largest diameter. In the case of nano-ZnO, the hydrodynamic diameter of nano-ZnO significantly increased with increased concentration levels. Also, after 7 days in a petri dish, according to the hydrodynamic diameter of the nano-TiO2 uptake, the hydrodynamic diameter of nano-TiO2 at the highest nano-TiO2 concentration significantly showed the largest diameter. Mature tomato (Lycopersicon esculentum) plants only showed the significant difference by nano-TiO2 at the highest Superoxide dismutase activity (SOD) in the highest (1000 mg/L) treatment. Also, mature tomato (Lycopersicon esculentum) plants and mature kidney bean (Phaseolus vulgaris) plants showed no significant differences by concentration levels of nano-ZnO. The chlorophyll contents of mature tomato (Lycopersicon esculentum) plants after either nano-TiO2 or nano-ZnO exposure of 7 days (mg/L) showed no significant differences with different concentrations of nanoparticles (nano-TiO2, nano-ZnO). And chlorophyll contents of mature kidney bean (Phaseolus vulgaris) plants after a nano-ZnO exposure of 7 days (mg/L) also showed no significant differences with different concentrations of nanoparticles (nano-TiO2, nano-ZnO). After an exposure of 5 weeks (mg/L), nano-TiO2 uptake by the mature tomato (Lycopersicon esculentum) plants was measured dividing plant parts by root, stem, leaf and fruit. At the root, leaf, fruit parts, there were no significant differences with different nano-TiO2 concentration levels. However, at the stem part, when nano-TiO2 concentration levels increased, the nano-TiO2 uptake of the mature tomato (Lycopersicon esculentum) plants decreased inversely. Also, after an exposure of 5 weeks (mg/L), the nano-ZnO uptake of the mature tomato (Lycopersicon esculentum) and kidney bean (Phaseolus vulgaris) plants was measured and only the mature tomato (Lycopersicon esculentum) plants showed significant differences. When the concentration of nano-ZnO increased, the uptake of nano-ZnO by the mature tomato (Lycopersicon esculentum) plants also increased. To confirm the results of the hydrodynamic diameter of the nano-TiO2 and nano-ZnO uptake, Pchem (Physical chemistry) datas (hydrodynamic diameter and zeta potential) were measured by ELS. In the case of nano-TiO2 in DW, when the concentration of nano-TiO2 increased, the hydrodynamic diameter of nano-TiO2 decreased. Nano-TiO2 in a Hoagland solution showed an increased hydrodynamic diameter of nano-TiO2 when the concentration of nano-TiO2 increased. Then, we also measured the hydrodynamic diameter of nano-ZnO in DW. When the concentration level of nano-ZnO increased, the hydrodynamic diameter of nano-ZnO decreased.

Key words: nano-TiO2 , nano-ZnO, Lycopersicon esculentum, Phaseolus vulgaris, antioxidant enzyme activities, Pchem