A new route for plant nutrient delivery20 June 2019, by Alexandra George

The pathway nanoparticles travel from the plant'sexterior to the soil. (PDF) Credit: Carnegie MellonUniversity

Agriculture around the globe requires newsolutions for food and water sustainability. Withmore frequent climate extremes, growingpopulations, increased food demand, and globalcrop threats, environmental engineers aresearching for solutions to manage food productionfor the future, starting at the tiniest level.

With current practices, up to 95 percent of appliedmicronutrients and 99.9 percent of appliedpesticides never reach their destinations and arewasted. They accumulate in the soil or run off intothe ground water and cause collateralenvironmental damage, degrade soil, and wastethe water and energy used in their production andapplication.

If growers could apply something to the leaf thatcould travel directly to the root, it could be a gamechanger for delivering nutrients, antibiotics and pesticides in a nearly 100 percent efficient way.Civil and Environmental Engineering ProfessorGreg Lowry, post-doctoral researcher Astrid

Avellan, and a team of researchers havesuccessfully discovered a way to apply nanoparticles to plant leaves so that they travelthrough the plant all the way to the root. Theirresults are published in a recent ACS Nano paper.

"The results from our paper really have thepotential to transform the way we deliveragrochemicals to plants," said Lowry.

This is the first time that anyone has systematicallystudied how nanoparticles move through the leaf,into the plant, to the root, and exude into the soil.

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X-ray fluorescence mapping of gold translocation onwheat leaves grown hydroponically and foliarly exposedfor 12 hours to gold nanoparticles coated in citrate(bottom) and PVP (top). Credit: Carnegie MellonUniversity

The research team sprayed gold nanoparticles witha polymer coating onto the leaves of young wheatplants. Plants don't need gold, but since golddoesn't exist anywhere in the plant, they were ableto easily identify where it traveled. They used wheatplants because they are an important crop in theUnited States and susceptible to nutrientdeficiencies.

Once the nanoparticles are sprayed onto the leaf,they move through the cuticle, which is the waxyouter layer covering the leaf. Then, it crosses theepidermis. The cuticle and epidermis are layers thatprotect the leaf from harm, prevent water loss, andallow gas exchange for the plant to breathe. Thenanoparticle then makes its way into the inner leaftissue, or mesophyll. Finally, it moves into thevasculature of the plant, or the plant's veins. Fromthere it can travel all the way down the stem andinto the root, or up to higher leaves.

For the first time, the researchers demonstratedthat once reaching the roots, nanoparticles can beexuded into the soil, adhering to themicroenvironment that sticks to the roots called therhizosphere. The rhizosphere is where the plantinteracts with the soil, takes in nutrients, releasessmall acids, carbon dioxide, and proteins, andwhere bacteria and fungi can enter the plant. Theonly methods currently available to treat anunhealthy rhizosphere are mixing agrochemicals inthe soil or applying water with the chemicals. Inboth cases a large amount of chemicals are lost.What the researchers have demonstrated is 100percent efficient delivery that can decrease theamount of chemicals needed, lower the cost, andlimit environmental contamination.

Image of wheat leaf after 7 days of exposure. The redindicates presence of gold nanoparticles. The top row offigure A were exposed to gold nanoparticles coated incitrate, and the bottom row of figure A were exposed togold nanoparticles coated in PVP. The images in figure Bindicate that the leaves exposed to PVP-coated goldnanoparticles no longer have gold on the surface of theleaf, meaning it has gone into the leaf. Credit: CarnegieMellon University

X-ray fluorescence mapping of gold translocation on

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wheat leaves grown hydroponically and foliarly exposedfor 12 hours to gold nanoparticles coated in citrate(bottom) and PVP (top). Red: Gold, Green: PotassiumCredit: Carnegie Mellon University

These tiny particles—which are smaller than 50nanometers—could be one very important key tosustainably feeding the 10 billion people projectedto be on the planet by 2050. For example, wheatplants growing in zinc-deficient soil turn yellow andcrop production decreases as plants start to die.But if you could deliver zinc oxide nanoparticlesthrough the leaves to reach the root, they couldexude into the soil and make both the soil and theplant healthy.

Farmers could also deliver antibiotics to the plant.Once a plant gets bacteria into its vasculature,there's little that can be done to save it. But ifantibiotic nanoparticles could be delivered throughthe leaves to get into the vasculature, they couldprevent or treat systemic bacterial diseases.

Nanoparticles are also more effective thanchemicals because engineers can design them tohave specific properties. For example, they coulddesign a nanoparticle that will stick to a leaf withoutdripping off when it rains. Or they can engineer thecoating on the outside of the particle to respond tomoisture or light. It is also possible to designnanoparticles that will be used in fewer quantitiesand are better for both the environment and humanhealth than the conventional agrochemicals usedcurrently. The possibilities are endless, and this isan important first step.

Delivering nanoparticles on plants in a 100 percentefficient way is part of Lowry's larger goals of atom-efficient agriculture (where every atom put on cropsis used and not wasted) and combating societalchallenges such as food insecurity.

"We're at this point where we've got to grow 80percent more food, on the same amount of land,with less pollution resulting from it," said Lowry."That's going to take a paradigm shift of the way wedo agriculture, and that's what we're trying to help."

More information: Astrid Avellan et al.Nanoparticle Size and Coating Chemistry ControlFoliar Uptake Pathways, Translocation, and Leaf-to-Rhizosphere Transport in Wheat, ACS Nano(2019). DOI: 10.1021/acsnano.8b09781

Provided by Carnegie Mellon University,Department of Civil and Environmental Engineering

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APA citation: A new route for plant nutrient delivery (2019, June 20) retrieved 16 November 2021 from https://phys.org/news/2019-06-route-nutrient-delivery.html

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