Technology that involves engineering plants to produce specific reactions and compounds through modification or addition is already used in the pharmaceutical industry, but a closer look at the capabilities that plants offer reveals further possibilities.
A new field of engineering, called plant nanobionics, might be little known at the moment, but could soon be implemented in several applications. It involves embedding non-native functions in plants by interfacing them with specifically designed nanoparticles, giving the plants enhanced abilities.
One potential application could be detecting explosives using spinach. This arises from a study done at Massachusetts Institute of Technology (MIT) entitled “Nitroaromatic detection and infrared communication from wild-type plants using plant nanobionics”. The researchers explain how they engineered spinach plants to act as “autosamplers of analytes in ambient groundwater and as infrared communication platforms that can send information to a smartphone”.
The researchers employ near-infrared fluorescent nanosensors, in the form of single-walled carbon nanotubes (SWCNTs), that are conjugated to peptides – compounds that contain two or more amino acids in a chain – to recognise nitroaromatics via infrared fluorescent emission.
Polyvinyl-alcohol SWCNTs are injected into the plant’s leaf. They act as reference signals when they become embedded within the leaf mesophyll, the inner tissue that contains chloroplasts.
When contaminant nitroaromatics are transported up the roots and stem into the leaf, they accumulate in the mesophyll and as a result there are changes in the intensity of fluorescence emissions. These changes are communicated wirelessly via infrared signals to a stand-off detector, such as a smartphone, that monitors the nitroaromatic fluctuations.
Min Hao Wong, one of the authors of the study, says: “The nanoparticles enter the plant by pressurising a solution onto the leaf using a needle-less syringe. The fluid enters pores in the surface of the leaf and fills a space called the mesophyll. The explosive flows from the ground into the leaf, triggering the detection.”
The purpose of the study was to establish the ability of plants to act as chemical monitors of groundwater and to communicate with electronic devices at stand-off distances.
Wong continues: “We tend to think of plants as being essentially static. The fact is that plants are enormous sources of information. They interact constantly with the environment that we live in, absorbing and accumulating various particulates and compounds, and responding to changes in temperature or humidity.
“Our goal is to show that humans can access this valuable information, and that plants can signal this information to us. In this role, plants serve as environmentally friendly, and net zero-carbon sensors of the environment that we live in.
“Applications may be found in precision agriculture. One application would be in high-density areas for surreptitious monitoring of threats.”
The researchers at MIT are now working to multiplex the sensors to detect dozens of different molecules. They are also working on turning the sensors inwards to monitor the plant’s health and its response to pathogens and pests.
Another MIT study entitled “Plant nanobionics approach to augment photosynthesis and biochemical sensing” describes how nanostructures can be used to triple the rate of photosynthesis, and enhance electron transport rates. This could prove useful in boosting crop yields.
Markita del Carpio Landry, one of the authors of the study, says: “Plant nanobionics is too new to have clear advantages or disadvantages. The degree to which nanomaterials can be interfaced with plants depends on the species, and the region of the plant – roots or leaves – in which nanomaterials are being introduced.”
An approach that engineers functions in plants could also be used as a manufacturing method. Recently, researchers at the University of York have developed a method to create “chemical factories” on the surface of leaves to make commercially useful products.
The team found that the final stages of the production of artemisinin, a substance used in anti-malarial drugs and naturally harvested from the plant Artemisia annua, is a spontaneous process and does not involve the actions of proteins to trigger a chemical reaction. This spontaneous process means that a very particular chemical environment must be created in order to produce and store often toxic chemicals in the plant.
The findings suggest that companies could use this “chemical factory” within the plant to make a host of chemical-based products, such as anti-bacterial gels, fragrances, natural sweeteners, and compounds to aid crop production.
Professor Ian Graham, who led the research at the university’s department of biology, says: “Plants make lots of high- value compounds but often in very small amounts. To produce these compounds on a commercial scale, biotechnologists aim to transfer the whole production process from plants to yeast cells which can then be grown at scale in large fermenters.
“Many of the valuable plant compounds, however, can be toxic to yeast cells. Our new findings suggest that we may have a solution to this problem.”
The “chemical factories”, called glandular trichomes, not only produce complex chemicals, but can store them without them being toxic to the plant.
The team also found that the pathway that produces artemisinin can be diverted to make entirely different products. The researchers argue that using the plant itself as the “factory” can work in creating products on a commercial scale.
Dr Tomasz Czechowski, co-author of the York research paper, says: “We have shown that Artemisia annua not only produces the most effective medicine to cure malaria but it can also be altered to produce other complex molecules, which is an exciting discovery.
“We now know that it employs a very sophisticated system that stores complex chemicals that could be used in many other products. This could pave the way for other plant-based products being made naturally within the plant itself.”
GE Pharmaceuticals plants acres of “pharma” crops for use in making specific medicines in prescribed amounts. Modified crops of rice, corn and tobacco, among other plants, can produce large amounts of proteins found in humans. Genetically modified rice, for example, can create proteins found in saliva and tears that could be made into medicines to treat stomach illnesses.
Other medicines that could be made include those that treat cystic fibrosis, anaemia and HIV, in addition to producing anticoagulants and hormones. Proteins produced from these modified crops could be used to manufacture plastics and detergents as well. Such crops could cut manufacturing costs by producing yields of chemicals in large amounts.
Although it might be a while before we see nanobionics blossom to their full potential, the manipulation and engineering of plant tissues and their chemical reactions are already being used by companies such as GE to make products such as medicines.