This is one in a series presenting news on technology and innovation, made possible with generous support from the Lemelson Foundation.
Plants typically endure long, blazing-hot days to produce the fruits and vegetables that growers desire. The incoming sun’s ultraviolet (UV) rays can be intense — enough to damage some crops. Such plants might benefit from a built-in sunscreen. Now a team of scientists in Australia has stepped in to lend a helping hand.
A family of nanoparticles known as metal-organic frameworks, or MOFs, can absorb harmful UV radiation. Joseph Richardson is a nano-engineer. He works in Melbourne at the Australian Research Council Centre of Excellence in Bio-Nano Science and Technology. Some MOFs, he knew, can turn UV rays into other wavelengths — ones that plants could use for photosynthesis. That’s the process by which plants produce food from light.
In theory, he could “feed” MOFs to the plants. The problem is, MOFs are too big for plant roots to take up. And cutting open the plants to load them with nanoparticles would damage their stems. So that was not an option.
Instead, he’s leading a research team working to make plants take up the building blocks of MOFs. Their goal: to help plants make their own MOFs. If those MOFs can capture the tissue-damaging UV rays, they might help crops survive tougher climates, both on Earth and in space.
It all began when Richardson realized the building blocks used to make MOFs are really small. They are so small that plant roots could slurp them up. His brainstorm: figure out a way to make these building blocks come together inside the plant and grow, on-site, into complete MOFs.
With that in mind, his team dissolved the starting materials — metal atoms and special carbon compounds — in water. They then placed plant cuttings into this solution.
“To our amazement, these simple materials were taken up by the plant, and grew into full-formed MOFs,” Richardson reports.
The scientists engineered these MOFs to fluoresce. They emit an intense green light when irradiated with UV light. This helped confirm the plants built the MOFs on-board. Under UV light, the entire plant fluoresced. Says Richardson, this showed that “MOFs formed in the roots, stems, leaves and other parts of plant.”
High-tech plants for tough conditions
The bigger question was whether this innovative way to seed the plant with MOFs would work as a sunscreen. To test that, they covered clippings of two plant species with MOFs. They then exposed the plants to UV light for three hours. Compared to uncoated clippings, the treated plants wilted less. Wilting is one indicator of plant damage, such as water loss due to the sun’s heat.
The new findings might boost the prospect of being able to grow food crops in space, Richardson says. (That would likely be necessary for long-term human missions.) The sun’s UV rays bombard the surface of Mars, for instance. But Mars lacks Earth’s thick, protective atmosphere to filter out dangerous amounts of that UV. So any plants there would likely shrivel and die.
MOF-carrying plants, however, should be able to withstand the UV onslaught. In fact, they should be able to use the MOFs’ altering of light wavelengths — both to make more food and for the plants’ protection.
Richardson and his team now plan to study the effects of MOFs on plant growth. “So far we haven't seen any damage to the plants. But all of our experiments were pretty short term,” he admits. “Now we’re looking at [possible] long-term damage — although we think it’s unlikely.”
Another big question relates to the safety of eating MOF-enriched plants. “MOFs can be toxic to humans, depending on what metal they are built around,” says Richardson. “But the ones we used have proven to be non-toxic to human cells, yeast and bacteria in lab tests.” Richardson also highlighted the fact that many labs around the world are looking to MOFs as a means for drug delivery in humans.
C. Michael McGuirk is more concerned about the long-term durability of MOFs. He’s a materials chemist at the Colorado School of Mines, in Golden. “Many MOFs break down over time and lose their unique structure and properties,” he explains, “especially in water.” Because water is vital for plant growth, MOF breakdown could pose a risk for crop production.
Even so, Richardson hopes MOF-embedded plants will one day help to feed people in hostile outposts, including space. “The plants that we are trying to create — plants that can withstand severe, high-UV environments — are certainly promising,” he says.
Richardson presented his team’s work at a meeting in April of the American Chemical Society in Orlando, Fla.
atmosphere The envelope of gases surrounding Earth or another planet.
atom The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and uncharged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.
carbon The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.
chemical A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.
climate The weather conditions that typically exist in one area, in general, or over a long period.
compound (often used as a synonym for chemical) A compound is a substance formed when two or more chemical elements unite (bond) in fixed proportions. For example, water is a compound made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O.
crop (in agriculture) A type of plant grown intentionally grown and nurtured by farmers, such as corn, coffee or tomatoes. Or the term could apply to the part of the plant harvested and sold by farmers.
defense (in biology) A natural protective action taken or chemical response that occurs when a species confront predators or agents that might harm it. (adj. defensive)
engineer A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need.
environment The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of things in the vicinity of an item of interest).
filter (in physics) A screen, plate or layer of a substance that absorbs light or other radiation or selectively prevents the transmission of some of its components.
fruit A seed-containing reproductive organ in a plant.
Mars The fourth planet from the sun, just one planet out from Earth. Like Earth, it has seasons and moisture. But its diameter is only about half as big as Earth’s.
metal organic framework (or MOF) A family of carbon-based chemicals that contain clusters of metal atoms. Those metal atoms can trap — and chemically react with — other compounds.
nanoparticle A small particle with dimensions measured in billionths of a meter.
organic (in chemistry) An adjective that indicates something is carbon-containing; also a term that relates to the basic chemicals that make up living organisms.
photosynthesis (verb: photosynthesize) The process by which green plants and some other organisms use sunlight to produce foods from carbon dioxide and water.
radiation (in physics) One of the three major ways that energy is transferred. In radiation, electromagnetic waves carry energy from one place to another, even across empty space.
risk The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)
tissue Made of cells, it is any of the distinct types of materials that make up animals, plants or fungi. Cells within a tissue work as a unit to perform a particular function in living organisms. Different organs of the human body, for instance, often are made from many different types of tissues.
ultraviolet A portion of the light spectrum that is close to violet but invisible to the human eye.
unique Something that is unlike anything else; the only one of its kind.
wavelength The distance between one peak and the next in a series of waves, or the distance between one trough and the next. It’s also one of the “yardsticks” used to measure radiation.
MEETING: J. Richardson and L. Kang. Nano-bionics: Assembly of functional metal-organic nanomaterials inside plants. Abstract # 732. Presentation at the American Chemical Society (ACS) Spring National Meeting & Exposition, April 3, 2019, Orlando, Fla.