Nano? NaYES!

Nanoparticles of zinc oxide (ZnO) may aid the use of organic Phosphorus in plants.

When we’ve covered stories about plants and nano particles/nanotechnology in the past it’s usually been from a rather pessimistic and doom and gloom laden point of view. For this item it is therefore pleasing to be able to redress the balance somewhat and to share a more positive and beneficial nanotech story, thanks to Ramesh Raliya et al.

Recognizing that inorganic phosphate (Pi) is a major limiting factor for plant growth, but wishing to avoid fertilization by adding Pi to the soil (whose global supply is severely constrained anyway), the team sought to enhance the innate capability of plants to make better use of the available organic P (Po). Accordingly, and imaginatively, they applied nanoparticles of zinc oxide (ZnO) to leaves of mung bean (presumably Vigna radiata, although bizarrely nowhere in the article was the experimental organism’s scientific name given*). But, what’s Zn got to do with P?

Vigna radiata
Vigna radiata, I presume? Mung Bean. Image by Earth100 / Wikipedia

Well, Zn is a co-factor for Po-mobilizing enzymes phosphatase and phytase released by plant roots. Foliar-feeding was employed to avoid ‘direct contact with the soil ecosystem’. And they found that activity of phosphatases and phytases was increased, by 84–108 %, and P uptake increased by 10.8 %. Since the ZnO used was biosynthesised by fungi – Aspergillus fumigatus TFR-8 (specifically, from cell-free fungal filtrate and ‘ZnNO3’) – this is another way that members of the fungal kingdom aid P-acquisition by angiosperms (i.e. it’s not just via mycorrhiza).

Furthermore, both, chlorophyll and total soluble protein content in ZnO-enhanced plants were increased by 34.5 % and 25 %, respectively. A double bonus then, since more chlorophyll should translate into more photosynthesis, hence harvestable yield…? Such ‘nanofertilised’ plants certainly had greater stem height, and root volume relative to the controls, which is yield of a sort; and, as a nutritionally-relevant benefit, more protein is definitely more yield. There’s a third/fourth (I’ve lost count!) bonus; Zn in part accumulated in the seed, which is eaten by people. Since Zn is an essential nutrient for humans, there is likely to be a boost to that organism’s nutrition if they feed on those Zn-enhanced mung beans (and arguably more so if leaves and/or stems are consumed, as Zn levels were higher in these plant fractions compared to the seeds).

And, root nodule number was increased by 58.9 % (Supplementary Information), which is potentially another bonus since these structures harbour N-fixing microbes, which might lessen the host plant’s dependency on added N fertiliser. Overall, nano-ZnO-‘phyllo-fertilization’ seems to work for mung beans, at a planting density of three to a pot. But, will it work large-scale, in an agricultural crop situation, for mung bean or other species..? Fingers’ crossed! And let’s hope we don’t run into a Zn-shortage to replace that P insufficiency which this nano-treatment is attempting to circumvent!

This interesting work is but one example of the potential use of nanotechnology in plant science, a topic reviewed by Peng Wang et al.

* Surely, it should be a rule – and one that is enforced – that scientific names of experimental organisms should be given – and ideally the full name with appropriate authority – in scientific reports, so that everybody knows unambiguously what was studied? After all, what’s the point of having scientific names if they’re not used?

Further reading

Ramesh Raliya, Jagadish Chandra Tarafdar, Pratim Biswas, 2016, 'Enhancing the Mobilization of Native Phosphorus in the Mung Bean Rhizosphere Using ZnO Nanoparticles Synthesized by Soil Fungi', Journal of Agricultural and Food Chemistry, vol. 64, no. 16, pp. 3111-3118

Josilaine Taeco Kobayashi, Sidinei Magela Thomaz, Fernando Mayer Pelicice, 2008, 'Phosphorus as a limiting factor for Eichhornia crassipes growth in the upper Paraná River floodplain', Wetlands, vol. 28, no. 4, pp. 905-913

Luis Herrera-Estrella, Damar López-Arredondo, 2016, 'Phosphorus: The Underrated Element for Feeding the World', Trends in Plant Science, vol. 21, no. 6, pp. 461-463

Dana Cordell, Jan-Olof Drangert, Stuart White, 2009, 'The story of phosphorus: Global food security and food for thought', Global Environmental Change, vol. 19, no. 2, pp. 292-305

Edward J Mullaney, Abul H.J Ullah, 2003, 'The term phytase comprises several different classes of enzymes', Biochemical and Biophysical Research Communications, vol. 312, no. 1, pp. 179-184

Minggang Li, Mitsuru Osaki, Idupulapati Madhusudana Rao, Toshiaki Tadano, 1997, Plant and Soil, vol. 195, no. 1, pp. 161-169

Julie E. Hayes, Alan E. Richardson, Richard J. Simpson, 1999, 'Phytase and acid phosphatase activities in extracts from roots of temperate pasture grass and legume seedlings', Australian Journal of Plant Physiology, vol. 26, no. 8, p. 801

Ramesh Raliya, J. C. Tarafdar, 2013, 'ZnO Nanoparticle Biosynthesis and Its Effect on Phosphorous-Mobilizing Enzyme Secretion and Gum Contents in Clusterbean (Cyamopsis tetragonoloba L.)', Agricultural Research, vol. 2, no. 1, pp. 48-57

S. E. Smith, I. Jakobsen, M. Gronlund, F. A. Smith, 2011, 'Roles of Arbuscular Mycorrhizas in Plant Phosphorus Nutrition: Interactions between Pathways of Phosphorus Uptake in Arbuscular Mycorrhizal Roots Have Important Implications for Understanding and Manipulating Plant Phosphorus Acquisition', PLANT PHYSIOLOGY, vol. 156, no. 3, pp. 1050-1057

W. Maret, 2013, 'Zinc Biochemistry: From a Single Zinc Enzyme to a Key Element of Life', Advances in Nutrition: An International Review Journal, vol. 4, no. 1, pp. 82-91

Nicholas J Brewin, 2010, ' Root Nodules (Legume- Rhizobium Symbiosis) ', Encyclopedia of Life Sciences

Peng Wang, Enzo Lombi, Fang-Jie Zhao, Peter M. Kopittke, 2016, 'Nanotechnology: A New Opportunity in Plant Sciences', Trends in Plant Science, vol. 21, no. 8, pp. 699-712