Uptake And Transportion Of CuO Nanoparticles In Rice(Oryza Sativa L.) Seedling And Its Toxicity Effects To Roots

Nanomaterials are widely used in various industries due to their size effect and unique physico-chemical properties. Nanomaterials have been released into the environment with their large-scale production and use. The occurrence of complex environmental behavior and ecological effects, bring unpredictable ecological impacts. In this paper, nano-copper oxide(nano-Cu O) was selected as the research object, and rice(Oryza sativa L.) was taken as the experimental crop, A hydroponics experiment was conducted by adding different concentrations of nano-Cu O(with the micron copper oxide(micron-Cu O) and the corresponding concentration of Cu2+ for control), and the uptake and accumulation of nano-Cu O by rice seedlings as well as its root toxicity effect were studied. The main results showed as follows:(1) The dissolution concentrations were 1.4 or 2.3 mg/L Cu2+ in the treatments of 10 and 100 mg/L nano-Cu O in 1/4 Hoagland nutrient solution, respectively. After adding nano-Cu O, micron-Cu O and Cu2+ into the nutrient solution, the concentration of copper in rice seedling in different treatments generally presented nano-Cu O > micon-Cu O > Cu2+, roots > shoots. The copper concentration of rice roots(351~1444mg/kg, dw) and shoots(9~45mg/kg, dw) in the treatment of nano-Cu O generally higher than those in micron-Cu O treatment(root: 248~817 mg/kg, dw; shoot: 1.57~1.60 mg/kg, dw) and Cu2+ treatment(root: 147~220 mg/kg, dw; shoot: 14~26 mg/kg, dw). The results of transmission electron microscope(TEM) images and energy dispersive spectrometer(EDS) analysis showed that nano-Cu O presented in root and stem of rice seedling, indicating rice could uptake, transport nano-Cu O through its primary form.(2) Nano-Cu O was mainly stored in the cell walls, the copper concentration in the cell walls ranged from 121 to 945 mg/kg, being higher by 1.7-2.2 times than those in the treatments of micron-Cu O and the corresponding Cu2+ treatment respectively. The copper concentrations in the cell walls increased with the increase of nano-Cu O concentrations. With nano-Cu O entering into the shoots, the copper concentrations in the order of cytoplasmic > cell wall > organelles.The copper concentrations in the cytoplasm varied from 6.7 to 31 mg/kg, accounting for 68%-72% of the total concentrations, which was higher by 11-28 times and 7-24 times than those of micron-Cu O and the corresponding Cu2+ treatments.(3) Concerning the chemical speciation, in the nano-Cu O treatments, copper mainly existed in the roots with the deionized water(53-619 mg/kg) and ethanol extractable fractions(91-257 mg/kg) which were more easily dissolved and more active. But in the corresponding Cu2+ tratment and micron-Cu O treatment, copper mainly existed in the roots with Na Cl and HCl extractable fractions which were more insoluble and relatively stable. After entering into the shoots, nano-Cu O existed mainly as ethanol extractable fraction which was more easily dissolved and more active, and the copper content was 16-37mg/kg(accounting for 45%-52% of the total concentration) being higher by 3-14 times than that of micron-Cu O treatment. This result indicate that the risk exsisted with nano-Cu O into the edible part of rice.(4) Under the treatments of Ca2+ channel inhibitor(La Cl3)、K+ channel inhibitor(TEA)、 endocytosis inhibitor(Na N3) and energy metabolism inhibitor(DNP), adsorption of nano-Cu O by the rice roots was firstly inhibited those inhibitors, with the inhibition ratios in order of La Cl3 > TEA > Na N3 > DNP. La Cl3 showed the strongest effect on the absorption of nano-Cu O(with the inhibition rate of 61%-92%), followed by Cu2+ treatment(57%-81%). To the uptake of nano-Cu O by rice, the inhibition rates by different inhibitors decreased in the order of La Cl3> Na N3 > DNP > TEA, and those to the shoots reduced in the order of La Cl3 > Na N3 > TEA > DNP. Endocytosis inhibitors and Ca2+ channel blockers inhibited the uptake of nano-Cu O by rice was more significant. The results indicated that nano-Cu O entered into rice via endocytosis channels as the primary form, and then through Ca2+ channels to the dissolution Cu2+ form.(5) A strong toxic effect of nano-Cu O was observed on the rice total root length, number of tips, apical bifurcation number, root volume, root surface area in the nano-Cu O treatment. The toxicity decreased generally as follows: nano-Cu O > micron-Cu O > Cu2+, and the inhibition ratio increases with the concentration increase. The inhibition ratio of root morphology varied from 28% to 74% in the nano-Cu O treatment, but the root diameter and root surface area was promoted by nano-Cu O. The most sensitive indicators were total root length, root volume and specific surface. Correlation analysis showed that the absorption of nano-Cu O and nano cumulative effect were the main reason for its toxicity in rice roots. Under the stress of low concentration(10mg/L) of nano-Cu O, root activity of rice seedlings increased significantly, there was no significant difference in the total absorption area and active absorption area. Under the high concentration nano-Cu O(100mg/L) stress, root activity of rice seedlings and total absorption area was significantly reduced.