Neutrons enable fine-tuning of pesticides to boost crop yields and reduce environmental impact. 8.09.2016

The wax surface on the leaves of plants, such as barley and wheat crops, acts as a protective barrier against environmental attacks including pests, and water and nutrient loss. The wax surface is also involved in the uptake and transportation of water and nutrients across the plant surface for plant growth. Therefore, the wax surface is paramount for the well-being and survival of all plants. Scientists at the University of Manchester have generated a model of the wax surface of leaves similar to those of wheat and barley crops, to better understand how pesticides modify these barriers in order to enter and protect the plants. The team conducted neutron reflectometry studies at the ILL and STFC ISIS facilities to examine the processes of water uptake in the wax films as present on the surface of plants.

The project yielded findings that show a way to develop advanced performance formulations, which will interact reversibly with plant surfaces and leave their protective cuticles unharmed. The results, titled ‘Structural Features of Reconstituted Wheat Wax Films’, have been published in the Royal Society journal, Interface.

This research involved the creation of a model of a leaf’s wax surface similar to those found in wheat crops. Through imaging techniques, it was evident to the team that the wax model strongly resembled the structure of the wax on a real leaf, indicating that it could be used to realistically study how water crosses the wax barrier and enter the plant. The model is now being used to study how surfactants, a key component in pesticide formulations, interact with the leaf surface to enter the plant and take effect. Neutron reflectometry, conducted on the ILL’s D17 reflectometer and the ISIS instrument INTER, was used to bounce neutrons off the surface of the wax model, to investigate what the wax film was made up of and how water crossed the barrier at the molecular level. This technique revealed that the wax was made up of a thin underlying film covered by large crystalline structures.

Neutron reflectometry was a unique and effective tool in this study, enabling not only the observation of the thickness of the wax films but also the change in density over the thickness range. This meant scientists were able to look at the amount of water penetrating into the leaf at the surface of the wax compared to the bottom of the wax closest to the epicuticular plant cells – giving a lot of information regarding how the water is diffusing through the plant.

D17 instrument scientist Philipp Gutfreund explains: “The D17 reflectometer is particularly suitable for the study of surface structures in solids and solid/liquid interfaces, making it most favourable for looking at the wax film in this study. Most excitingly, D17 has the ability to use a 2D detector to indirectly view the sub-micrometer sized surface extrusions and confirm their existence by making use of a phenomenon called Yoneda scattering. This was a major breakthrough in the project.

The advantage of using a 2D detector is that one sees not only the mirror reflection of neutrons, which bears information about the out-of-plane structure of the thin film, but the ‘diffusely’ reflected neutrons are recorded too. These additional features in the scattering pattern are mainly concentrated around a certain ‘critical’ reflection angle, the Yoneda-peak, giving complimentary information about the in-plane structure of the wax film.”

This is the first time anyone has used extracted waxes to recreate the wax shield that plants use for protection. As a result, the new tool enables scientists to study how pesticides enter plants by crossing the wax barrier on leaves. Further, the breakthrough it is another step towards fine-tuning the chemicals used in agriculture to maximise crop yields without damaging the plants. By understanding how surfactants in pesticides interact with the plant, fine-tuning of the ingredients in pesticides is possible - to not only further increase crop yield but also to remove some potential negative side effects, including the removal of some of the waxes which leave the plant susceptible to diseases and attack from bacteria and microbes. This opens the door to crop-safe formulations which will reversibly interact with the plant waxes.

Pesticides are utilised by farmers as an additional layer of protection against pests, which as a result further optimises their yields. They play a crucial role in ensuring that plants can maintain the maximum area possible of green leaf for photosynthesis, which is the process that transforms the sun’s energy into food. In turn, this is protective for the well-being of the plants, as it prevents the loss of leaf surface area to pests and diseases and given the growing global population, can help increase crop yield to meet food demand.

Instrument: D17 - Neutron reflectometer with horizontal scattering geometry

Re.: Journal of the Royal Society Interface. DOI: 10.1098/rsif.2016.0396

Contact:Dr Philipp Gutfreund

Notes to Editors:

About ILL – the Institut Laue-Langevin (ILL) is an international research centre based in Grenoble, France. It has led the world in neutron-scattering science and technology for almost 40 years, since experiments began in 1972. ILL operates one of the most intense neutron sources in the world, feeding beams of neutrons to a suite of 40 high-performance instruments that are constantly upgraded. Each year 1,200 researchers from over 40 countries visit ILL to conduct research into condensed matter physics, (green) chemistry, biology, nuclear physics, and materials science. The UK, along with France and Germany is an associate and major funder of the ILL.