Exposure of Commercial Titanium Dioxide and Copper Hydroxide Nanomaterials on Basil (Ocimum basilicum): A Life Cycle and Transgenerational Study

摘要

Although thousands of reports have shown that engineered nanomaterials (ENMs) can alter several agronomical, physiological, and biochemical parameters in plant and mammal systems, the effects of long-term exposure and varietal responses are scarce. Titanium dioxide nanoparticles (nano-TiO2) and copper hydroxide nanoparticles [nano-Cu(OH)2], which are widely used in agriculture, medicine, food industry, textile, among other areas, are among the ENMs with high production and consumption globally. Though reports indicate that these ENMs affected plant development and metabolism, their interactions with basil (Ocimum basilicum) are unknown. Basil is a popular culinary herb worldwide, featured in Asian and European cuisine and has more than 30 varieties. This research project was performed to investigate the changes in plant growth, nutritional compounds, biochemical responses, and the accumulation of Ti and Cu in long-term (life cycle and transgenerational) exposure. This research project was undertaken into three parts: Part I was aimed at examining the effects of root exposure of nano-TiO2 with different surface properties (pristine, hydrophobic, and hydrophilic) at the concentration of nanoparticles ranging from 0~750 mg˙kg-1. Part II was conducted to determine the transgenerational effects of the corresponding nano-TiO2 at 750 mg˙kg -1. Plants in Part I and II were harvested at the flowering stage and analyzed for element content, enzymatic activity, photosynthesis, and macromolecular content. In Part III, two varieties (Dark Opal and Dulce) of basil were analyzed for the responses to the foliar exposure of 4.8 mg Cu/pot of Cu(OH)2 nanowires, CuPro [Cu(OH)2 bulk], and CuSO4 suspensions/solutions. In this part, plants were harvested at the pruning stage, and GC-MS analyses were conducted on leaves to investigate variety-dependent metabolic responses. Results from Part I suggest that these three nano-TiO 2 resulted in concentration-dependent Ti accumulation in roots, with preferential uptake of hydrophobic nano-TiO2. At 750 mg˙kg -1, lower total sugar content was determined in the plants treated with pristine (32%), hydrophobic (38%), and hydrophilic (66%) nano-TiO 2, compared with control. Besides, lower reducing sugar (34%) and starch content (25%) was yielded by pristine and hydrophobic nano-TiO2, respectively. In Part II, higher stomatal conductance was determined (214%) in the plants exposed to pristine nano-TiO2 in two cycles, while hydrophobic and hydrophilic nano-TiO2 resulted in lower total chlorophyll content in plants exposed to the corresponding nano-TiO2 in the first cycle (24% and 30%, respectively). In addition, higher total sugar was determined in plants exposed to hydrophilic nano-TiO2 in both cycles (80%). Compared with plants that were never exposed to nanoparticles, significantly higher Ti was determined in the roots of plants exposed to the three nanoparticles in the first cycle. Nevertheless, higher Ti was only determined in the roots of plants treated with pristine nano-TiO2 in two consecutive cycles. None of the treatments in Part I and II resulted in higher Ti translocation to shoots, which indicates lower risks for humans to uptake these nanoparticles. Results of Part III showed that in low anthocyanin plants, copper remained in the leaves and none of the compounds affected the anthocyanin and essential oil content. In addition, CuSO4 and Cu(OH)2 nanowires increased six types of fatty acids, while CuPro decreased two types of fatty acids. In the high anthocyanin variety, copper translocated from leaves to stems and roots, and the three compounds reduced anthocyanin and essential oil contents. Moreover, six types of fatty acids were reduced by the three copper compounds at different degrees. The alterations in nutritional molecules by these ENMs suggest that people who rely on nutritional supplement, through dietary intake, might be affected. It is expected that these findings shed light on the long-term and transgenerational effects of ENMs in crop plants.