Inexpensive Silk Microneedles Deliver Amendments to Plants
When farmers apply substances to their crops, 30 to 50 percent of the chemicals end up in the air or soil instead of on the plants. A team of researchers from MIT and Singapore has developed a much more precise way to deliver substances to plants: tiny needles made of silk.
In a study published in Nature Nanotechnology, the researchers developed a way to produce large amounts of these hollow silk microneedles. They used them to inject agrochemicals and nutrients into plants, and to monitor their health.
The team used the technique to give plants iron to treat a chlorosis and to add vitamin B12 to tomato plants to make them more nutritious. The researchers also showed the microneedles could be used to monitor the quality of fluids flowing into plants and to detect when the surrounding soil contained heavy metals.
Overall, the researchers believe the microneedles could serve as a new kind of plant interface for real-time health monitoring and biofortification.
Accessing the inner tissues of living plants requires scientists to get through the plants’ waxy skin without causing too much stress. In previous work, the researchers used silk-based microneedles to deliver agrochemicals to plants in lab environments and to detect pH changes in living plants. But these initial efforts involved small payloads, limiting their applications in commercial agriculture.
Hollow structures could increase the amount of chemicals microneedles can deliver, but creating those structures at scale has historically required clean rooms and expensive facilities. For this study, the research team created a new way to manufacture hollow silk microneedles by combining silk fibroin protein with a salty solution inside tiny, cone-shaped molds. As water evaporated from the solution, the silk solidified into the mold while the salt formed crystalline structures inside the molds. When the salt was removed, it left behind in each needle a hollow structure or tiny pores, depending on the salt concentration and the separation of the organic and inorganic phases. The simple fabrication process can be done outside of a clean room.
In addition to injecting substances into plants, the researchers explored the use of their microneedles to monitor the health of plants by studying tomatoes growing in hydroponic solutions contaminated with cadmium, a toxic metal commonly found in farms close to industrial and mining sites. They showed their microneedles absorbed the toxin within 15 minutes of being injected into the tomato stalks, offering a path to rapid detection.
Current advanced techniques for monitoring plant health, such as colorimetric and hyperspectral lead analyses, can only detect problems after plant growth is already being stunted. Other methods, such as sap sampling, can be too time-consuming. Microneedles, in contrast, could be used to more easily collect sap for ongoing chemical analysis. For instance, the researchers showed they could monitor cadmium levels in tomatoes over the course of 18 hours.
Microneedles Also Extend Shelf Life of Produce
Researchers from MIT have shown they can extend the shelf life of harvested plants by injecting them with melatonin using biodegradable microneedles. Their findings will appear in Nano Letters.
More than 30 percent of the world’s food is lost after it’s harvested — enough to feed more than 1 billion people. Refrigeration is the most common way to preserve foods, but it requires energy and infrastructure that many regions of the world can’t afford or lack access to.
The researchers believe their system could offer an alternative or complement to refrigeration. Central to their approach are patches of silk microneedles. The microneedles can get through the tough, waxy skin of plants, without causing a stress response, and deliver precise amounts of melatonin into plants’ inner tissues.
The researchers applied small patches of the microneedles containing melatonin to the base of the leafy vegetable pak choy. After application, the researchers found the melatonin was able to extend the vegetables’ shelf life by four days at room temperature and 10 days when refrigerated. This could allow more crops to reach consumers before they’re wasted.
Aside from helping humans sleep, melatonin is also a natural hormone in many plants that helps them regulate growth and aging. The researchers used a dose so low that it’s fully metabolized by the crop and would not affect humans. Pak choy is typically harvested by cutting the leafy plant from the root system, exposing the shoot base, which provides easy access to vascular bundles that distribute water and nutrients to the rest of the plant.
At room temperature, the leaves of an untreated control group began yellowing within two or three days. By the fourth day, the yellowing accelerated to the point that the plants likely could not be sold. Plants treated with the melatonin-loaded silk microneedles, in contrast, remained green on day five, and the yellowing process was significantly delayed. The weight loss and chlorophyll reduction of treated plants also slowed significantly at room temperature. Overall, the researchers estimated the microneedle-treated plants retained their saleable value until the eighth day. In refrigerated conditions of about 40 degrees Fahrenheit, plant yellowing was delayed by about five days on average, with treated plants remaining relatively green until day 25.
“Spectrophotometric analysis of the plants indicated the treated plants had higher antioxidant activity, while gene analysis showed the melatonin set off a protective chain reaction inside the plants, preserving chlorophyll and adjusting hormones to slow senescence,” said researcher Monika Jangir.
Microbes on Sand Grains Remove Anthropogenic Nitrogen in Oceans
Sometimes nature cleans up our mess.
Human activities, such as agriculture, have dramatically increased nitrogen inputs into coastal seas. Microorganisms remove much of this human-derived nitrogen in coastal sands through a process called denitrification. Denitrification generally only occurs in the absence of oxygen.
However, scientists from the Max Planck Institute for Marine Microbiology discovered that it also happens in oxygenated sands, via a thus far unknown mechanism. Bunches of microbes, unevenly distributed on the surface of sand grains, use up all the oxygen around them, thus creating anoxic microenvironments in which other microbes can carry out denitrification. The results were published in the journal Scientific Reports.
The scientists used a method called microfluidic imaging, which allowed them to visualize the diverse and uneven distribution of microbes and the oxygen dynamics on extremely small scales. “Tens of thousands of microorganisms live on a single grain of sand. We were able to distinguish oxygen-consuming and oxygen-producing microbial colonies located within micrometers of each other,” explained researcher Farooq Moin Jalaluddin. “Our estimates based on model simulations show that anaerobic denitrification in these anoxic pockets can account for up to one third of the total denitrification in oxygenated sands.”
This mechanism is a significant sink for the excess human-produced nitrogen that enters our oceans.
There Are Consequences of Overplanting Bt Corn
A new study from Michigan State University shows that planting too much genetically modified corn, which was designed to fight off a tough insect — the corn rootworm — especially in the eastern U.S. Corn Belt states, may be causing more harm than good.
Bt corn was created to produce natural pesticides, through the introduction of genes from a soil bacterium called Bacillus thuringiensis. Some varieties of Bt corn kill corn rootworms by making the roots poisonous to them. But after years of research across 10 states in the U.S. Corn Belt, scientists have found that the more this corn is planted, the less effective it becomes.
The research team found that farmers are planting more Bt corn than they need to, especially in the eastern Corn Belt states —- Ohio, Michigan and Pennsylvania — with no added benefit and higher seed costs. These eastern states don’t have nearly as much of a corn rootworm problem as the major corn producers in the West, which include Iowa, Illinois and Nebraska. The more Bt corn planted, though, the more likely pests evolve resistance to it via selection pressure. The strong insects that survive breed more insects that are resistant to Bt.
The researchers estimate that reducing the Bt planting rate from 50 to 18 percent in eastern states could have saved farmers $99 million in one-year benefits and $1.98 billion in lifetime benefits.
Human-Caused Dust Events Are Linked to Fallow Farmland
An average of more than 1 million acres of idle farmland a year is a significant contributor to a growing dust problem in California that has implications for millions of residents’ health and the state’s climate.
A new study published in Communications Earth and Environment by UC Merced researchers finds that the Central Valley accounts for about 77 percent of fallowed land in California and is associated with about 88 percent of major anthropogenic dust events.
“Idled farmland and dust are particularly concentrated in Kern, Fresno and Kings counties, where annual crops such as wheat, corn, and cotton are fallowed as part of agricultural practices or a combination of water and economic decisions,” said Abatzoglou, a climatologist in the Department of Management of Complex Systems in the School of Engineering. “When fields are unplanted, wind erosion can create dust.”
Unplanted, dry fields are far more susceptible to erosion via the wind. Dust can be laced with chemicals and pathogens that cause severe respiratory illnesses or death. For example, Valley fever, caused by a fungus, relies on dust to spread. Particulate matter has also been linked to various forms of dementia, cardiovascular problems, COPD, asthma, and perhaps surprisingly, longer and more painful menstrual cycles.
In addition to health problems, a significant reduction in visibility during dust storms has resulted in fatal traffic accidents. Dust storms can also reduce agricultural productivity due to the loss of fertile topsoil and abrasion of crops by airborne particles.
Although researchers don’t fully understand dust’s effects on climate, they do know that when dust settles on the Sierra Nevada snowpack, it darkens the snow and encourages melting earlier in the year than usual. That impacts critical water resources for people around the state.
Fallowed acreage varies year to year, but the researchers found that the geographic coverage of these unfarmed lands expanded between 2008 and 2022, and that growth could be linked to an increase in dust activities. The expansion of unplanted lands is partly due to the Sustainable Groundwater Management Act, which requires farmers to limit the water they use yearly. The researchers suggested farmers consider cover crops or ground cover that increases soil health and reduces dust.
Ecology in Action: Tree Cover Reduces Mosquito-Borne Health Risk
Protecting trees might not seem like a public health strategy, but new research suggests it could be — especially in the tropics. A Stanford University-led study published in Landscape Ecology shows that in Costa Rica, even modest patches of tree cover can reduce the presence of invasive mosquito species known to transmit diseases like dengue fever. The illness often brings flu-like symptoms and can escalate to severe bleeding, organ failure and even death without proper medical care. The findings can inform land use decisions and tree preservation strategies in rural areas.
Using field observations and satellite data on land cover for a patchwork of forests, farms, and residential areas in southern Costa Rica, the researchers found the presence of the Aedes albopictus mosquito, a dengue vector, decreased in areas with more tree cover, while the total number of mosquito species increased. That’s because more species leads to more competition, making it harder for an invasive species to find unoccupied space or resources, such as food or breeding sites. Also, more diverse environments are often more stable and resilient to disturbance, making them less hospitable to fast-spreading, opportunistic invaders like Aedes albopictus.
The study’s findings offer a potential win-win strategy: protecting trees can help conserve biodiversity while also reducing the likelihood of disease transmission. That is good news in the face of warmer temperatures, changes in rainfall, and human activity that are enabling the spread of mosquito-borne illnesses to new places often unprepared to deal with them.
