Researchers
at the Adolphe Merkle Institute and the Department of Biology at the University
of Fribourg have discovered how certain silica nanoparticles could act as a
traceless, degradable, and highly efficient treatment against some plant
pathogens.
One of the
biggest challenges facing agriculture today is the extensive use of fertilizers
and pesticides. With an increasing number of products banned or considered
dangerous for human and animal health, the need for substitutes is acute. One
approach is to stimulate plants' own immune response to pathogen attacks.
Silicic acid, which naturally occurs in soil, is known to provoke such
responses in plants, and amorphous silica nanoparticles can release this
substance in small amounts. These nanoparticles, which are also naturally
present in many food crops such as cereals, are more common than most people
think. They are part of food grade silica (SiO2), otherwise known as E551 on
labels and packaging, and used for decades in a variety of products such as
table salt, pills, or protein powders to avoid clumping.
Increased
resistance
With this
in mind, the Fribourg-based researchers aimed to create an environmentally safe
nano-agrochemical for the targeted delivery of silicic acid and to stimulate
plant defense. They synthesized silica nanoparticles with similar properties to
those found in plants. To test their efficiency, they applied the nanoparticles
on Arabidopsis thaliana (thale cress), a widely used plant model, infected with
the bacterial pest Pseudomonas syringae, another model organism. The results
showed that their nanoparticles can boost resistance against the bacteria in a
dose-dependent manner by stimulating the plant's defense hormone, salicylic
acid (which is also the active ingredient in aspirin). The researchers also
investigated the interactions of the nanoparticles with plant leaves. They were
able to show that nanoparticle uptake and action occurred exclusively through
the leaf pores (stomata) that allow the plants to breathe. The nanoparticles
did not distribute further in the plants, and the particles degrade without
leaving a trace in the presence of water, an important consideration for
environmental and food safety. Compared to free silicic acid, which is already
used in crop protection, the silica nanoparticles caused less stress to the
plants and to other soil microorganisms due to the slow release of the silicic
acid. The study, published in the top-ranking journal Nature Nanotechnology,
shows that silica nanoparticles could serve as an inexpensive, highly
efficient, safe, and sustainable alternative for plant disease protection.
Future
research could extend the investigations to a broader spectrum of plant
pathogens according to the researchers such as other bacteria, insects, or
viruses. They emphasize though that before any broad application of
nanoparticles as nano-biostimulants and -fertilizers, a thorough analysis is
needed to assess the potential long-term fate of silica nanoparticles in the
environment.