Methods of Using Nanoparticles
4.2 Incubation .1 Via Seeds
4.2.2 Via Roots
The root, especially root hair, is the most essential plant organ dealing with the uptake of nutrients. Nutrient ions are transported to the core of the root (stele) for them to reach the conducting xylem and phloem tissues. Xylem is responsible for the movement of water and inorganic molecules, whereas phloem accounts for organic molecule transportation across the plant body. Nanoparticulate exposure through the roots is thought to provide direct access to the conductive tissues, which would facilitate the efficient translocation of NPs to the desired tissues or throughout the plant body.
2,4-dichlorophenoxyacetic acid (2,4-D)-induced leaf senescence and its inhibi-tion by silver (Ag+) ions in the form of silver nitrate (AgNO3) or silver nanopar-ticles (Ag NPs) were analyzed in 8-day-old mung bean (Vigna radiata) seedlings.
Fig. 4.2 Effects of GO on seed germination and development in Arabidopsis. a Effects of GO on seed germination at 48 h. b Effects of GO on seed sprouting at 36 h. Reprinted from Zhao et al.
(2015b), with permission from Elsevier
Table 4.1 Examples of nanomaterial exposure directly to seeds
Gold NPs (Au NPs) Soybean Seeds were exposed to NP
CeO2NPs Maize Maize plants
grown in soil
ZnO NPs Green Peas Seeds exposed
to NPs mixed
Au nanoclusters Bean sprouts Seeds were germinated in medium supplemented with NPs
Sensing ferric ions (Su et al.2015)
(continued)
Seeds were germinated on double-distilled water-moistened cotton pads for 48 h.
Eight-day-old seedlings received a single application of 18 mL (twice a day) solutions of 2,4-D, indole acetic acid (IAA), AgNO3,and Ag NPs, either alone or in Table 4.1 (continued)
Nanoparticles Plant Method Objective Reference
CeO2and ZnO NPs Cucumber NPs mixed with soil and
CeO2NPs Radish Plants were
cultivated in
Mn NPs Mung bean Seeds imbibed
in NP solution
CeO2and ZnO NPs Maize Plants were cultivated in
combination. After eight days, seedlings were harvested and used for analysis (Karuppanapandian et al.2011).
Peralta-Videa et al. (2014) determined the nutrient composition in soybean plants cultivated in farm soil amended with nCeO2at 0–1000 mg/kg and nZnO at 0–500 mg/kg. 10 nm nZnO and 8 nm nCeO2NPs in powder form were mixed with soil approximately 24 h before planting. 2.4 kg of individual soil samples were placed in polyethylene bags with drainage holes and placed within 4-L polyethylene/polypropylene blend garden pots previously bottom-filled with 400 g of washed gravel (1.25–2.5 cm). Dwarf soybean seeds (Early Hakucho, variety product no. 5555) were prior-germinated in peat pellets and transferred to the NP soil pots, 18 days after planting. The plants were harvested after 48 days of growth in the NP-treated soil and respective samples used for analysis.
In their research, Torre-Roche et al. (2013) analyzed the effect of nanoparticle, bulk, or ionic Ag exposure on dichlorodiphenyldichloroethylene (p, p′-DDE; DDT metabolite) accumulation by soybean and zucchini. Before transplanting for exposure assay, the seeds were pre-germinated in vermiculite for 5–7 days. 125-mL jars with 12 g of dry vermiculite (approximately 80 mL) were amended with 20 or 40 mg of bulk or NP Ag to achieve concentrations of 500 and 2000 mg/L (based on 40 mL of added solution) and mixed thoroughly. Zucchini and soybean seedlings were gently planted in the vermiculite (one plant per jar). The soil mixture was then supplemented with 40 mL of 25 % Hoagland solution containing 100lg/L DDE, yielding Ag bulk and NP concentrations of 500 or 2000 mg/L. Post-19 days of growth period, the plants were harvested for further experiments. The same group (Torre-Roche et al.
2012) performed similar experiments to assess the effect of C60fullerene exposure on the accumulation of p, p′-DDE by zucchini, soybean, and tomato. The plants were grown in 125-mL jars of vermiculite amended with 0 or 40 mg of C60fullerenes.
The effects of Ag NPs on two important crop plants, mung bean and sorghum (Sorghum bicolor) were analyzed in both agar and soil media (Lee et al.2012). Ag NPs were selected for this study due to their designation as an OECD priority nanomaterial. Also to note is that, sorghum and mung bean are recommended by the OECD (Paris, France) and the American Society for Testing Materials (ASTM).
Pre-sterilized seeds were germinated on moist cotton, and after 24 h, the sprouted seeds were used in the tests. Petri plates with 30 mL of agar culture media and specified concentrations of nanoparticles were prepared. Ten seedlings were inoc-ulated just above the surface of the agar plates and incubated at culture conditions for two days, after which the plants were separated from the agar, washed thor-oughly, and used for further analysis.
Nair and Chung (2015) investigated the impact of CuO NPs in mustard (Brassica juncea) plants. Pre-sterilized seeds were germinated on wet Whatman No. 1 paper. Different concentrations of CuO NPs (0, 20, 50, 100, 200, 400, and 500 mg/L) were added to the pre-autoclaved, half-strength, semi-solid MS medium and mixed thoroughly by vortexing. Ten germinated seeds were placed in culture vessels with the spiked media and cultured for 14 days. Enhanced lignification of both shoot and root cells was observed and was speculated to have been the result of an increase in cell wall rigidity and hormonal imbalances as well as inhibition of
mineral uptake to the plants due to the NP exposure. It has to be acknowledged that despite the ever-increasing publications addressing NPs–plant interactions, the implications of NPs on the nutritional parameters of food crops have been limited.
Rico et al. (2013) analyzed the quality of rice grains harvested from plants culti-vated in cerium oxide NPs (nCeO2) supplemented soil. Three rice varieties (high, medium, and low amylose) were grown in soil supplemented with nCeO2at 0 and 500 mg kg−1soil. Plastic pots (24 cm diameter 25 cm high) containing 5 kg of soil (Earthgro potting soil) and nCeO2 suspension at a final concentration of 500 mg kg−1were readied. The mixture was equilibrated for three days before rice seedling transplant. Regular irrigation of the soil–NP mixture was done with dis-tilled water to maintain saturation. Thirty-day-old seedlings were transplanted into the pots, fertilized with 200 mL of Yoshida nutrient solution per week, and placed in a greenhouse. After 135 days, the grains were harvested and dried at 80 °C and brown rice, obtained by removing the rice hull, was powdered, sieved to pass mesh number 4, and utilized for experimental analysis. Rico et al. (2014) conducted similar experiments with nCeO2 on growth and yield attributes and nutritional composition in wheat (Triticum aestivum). Wheat was cultivated till maturity and grain production in soil spiked with 0, 125, 250, and 500 mg of nCeO2/kg. At harvest, grains and tissues were analyzed for mineral, fatty acid, and amino acid content. Additional examples of NM exposure to roots are tabulated in Table4.2.