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Scientists are conducting extensive research on developing metal-based and carbon-based nanomaterials to improve plant growth and development. Nanomaterials can be used as promising tools to deliver genes (required for proper plant functioning) or chemicals to the target site, with high accuracy in a controlled manner.
Various morphological and physiological changes are found in plants exposed to nanomaterials. The variation in their functional expression depends on several parameters, such as the properties of nanoparticles, host plant and specific type of nanoparticle interaction, surface coating, size, dosage, time of exposure, and many more.
A complete understanding of the dynamics of plant-nanoparticle interaction is still not clear. However, some of the research report both positive and negative effects of nanoparticles on plant function and development.
Positive Effects of Nanoparticles on Plants
Nanotechnology has a role in solving different environmental and health issues which occurs with the excessive usage of chemical fertilizers in agricultural practices. Many nanoparticles, including carbon nanotubes, silver, titanium oxide, gold, sulfur, zinc, iron, silica, apatite, copper, chitosan- NKP- nanoparticles and carbon nanotube coated NKP+ chitosan NPK- nanoparticles show improved plant growth and an increase in crop production when used in the proper concentrations.
Some of the other positive effects of different nanoparticles on plant functions are:
- Seed germination: High germination rates are seen in seeds of aged spinach soaked in a high concentration of TiO2 nanoparticle solution. This treatment promotes the growth of spinach and accelerates nitrogen assimilation. The reaction mechanism involves excitation in the oxygen evolution rate in spinach chloroplasts, which improves chloroplast coupling and enhances the activities of Mg2+-ATPase and chloroplast coupling factor on the thylakoid membranes. This nanoparticle also protects chloroplasts from aging for an extended period of light.
- Rate of photosynthesis: Significant higher activity of Rubisco – an enzyme involved in carbon fixation - is seen in spinach plants treated with nano-anatase. An increase in the rate of electron transfer, oxygen evolution, and photophosphorylation is also reported. Elevation in the protein levels and activity of Rubisco leads to the improvement of Rubisco carboxylation and the rate of photosynthetic carbon reaction rate increases.
- Plant biomass and root elongation: An increase of root length, number of fronds, and overall biomass of Lemna minor (duckweed) are seen on the application of alumina nanoparticles. This development of biomass was due to increased efficiencies in photosynthesis. Alumina nanoparticles increase the quantum yield of photosystem II. Similarly, in radish and rape, a significant enhancement in root length is seen on the application of aluminum nanoparticles.
- Increase in production: Application of nano-iron oxide particles results in the highest grain yield, showing a 48% increase in comparison with control. This could be because nano-iron oxide can facilitate the photosynthate and iron transferring to the leaves.
- Phytostimulatory effect of nanoparticles on flowering: Nanoparticles possess unique biological properties that may act as a plant growth stimulator. Soaking the bulbs in a silver nanoparticle solution is an effective strategy to promote plant growth and flowering. Plants treated with silver nanoparticles showed a higher number of flowers and flowered for longer.
Negative Effects of Nanoparticles on Plants
Many researchers reported the adverse effect of nanoparticles on plant function, some of which are discussed below.
- Plant growth inhibition: The study of cytotoxic and genotoxic impacts of silver nanoparticles (below 100 nm size) using root tip cells of Allium cepa shows that higher concentration of the nanoparticles decreases the mitotic index. The silver nanoparticles disrupt stages of cell division, causing disturbed metaphase, chromatin bridge, multiple chromosomal breaks, and cell disintegration. Copper oxide nanoparticles induce DNA damage in agricultural and grassland plants.
- Inhibition of seed germination: Significant inhibition of seed germination is induced by the smaller, monodisperse nano-zinc oxide particles.
- Reduced pigment production in plant: Copper oxide nanoparticles decreases chlorophyll concentration in plants.
- Photosynthesis: In Elodea densa (Planch) plants, lipid peroxidation was enhanced on the application of copper ions and copper nanoparticles. At a higher concentration, an accumulation of nanoparticles by the plants causes an increase in catalase and superoxide dismutase activities and a decrease in photosynthesis.
- Disruption in root system: The phytotoxicity study of cobalt and zinc oxide nanoparticles on the roots of Allium cepa (onion bulbs) show that increasing concentrations of the nanoparticles inhibit the elongation of the roots with respect to control plants. The phytotoxicity of cobalt oxide nanoparticles could be because such nanoparticles could block the water channels through adsorption, while the zinc oxide nanoparticles possibly infiltrate radically into onion roots and spoil the whole cellular metabolism and stages of cell division.
References and Further Reading
Singla, R., Kumari, A. and Yadav K, S. (2019). Impact of Nanomaterials on Plant Physiology and Functions. Springer International Publishing.
Masarovičová, E. and Kráľová, K. (2013). Metal nanoparticles and plants. Ecological Chemistry and Engineering S. 20, 9–22.
Salachna, P., Byczynska, A., Zawadzinska, A., Piechocki, R.and Małgorzata Mizielinska. (2019). Stimulatory Effect of Silver Nanoparticles on the Growth and Flowering of Potted Oriental Lilies. Agronomy. 9, 610.