Engineers at the University of California San Diego have unveiled a groundbreaking spray-on polymer coating designed to bolster plants against harmful bacterial infections and enhance their resilience to drought conditions. This significant advancement, detailed in the journal ACS Materials Letters, holds the potential to fortify global food security amid escalating environmental stresses that exacerbate plant disease pressures.
Bacterial infections pose an increasing threat to agriculture, contributing to substantial crop losses worldwide. These infections, driven by both Gram-negative and Gram-positive bacteria, lead to devastating plant diseases such as wilt, blight, speck, and canker. Rising global temperatures are further enabling pathogens to invade new regions, thereby exposing crops to a broader array of infections.
Developing a Plant-Safe Antibacterial Coating
To address this pressing challenge, researchers from the University of California San Diego, including professors Jon Pokorski and Nicole Steinmetz, collaborated to create an antibacterial coating that can be applied directly to plant leaves. This effort was part of the UC San Diego Materials Research Science and Engineering Center (MRSEC) initiative.
The innovative coating is crafted from a specially designed synthetic polymer featuring positively charged chemical groups with inherent antibacterial properties. These groups disrupt bacterial cell membranes, making the coating effective against a wide range of harmful microbes.
Innovative Synthesis Method
Creating a plant-friendly spray coating was achieved by modifying a common polymer synthesis method to operate under gentle, water-based conditions. “Typically, polymers are synthesized using organic solvents that are toxic to plants,” explained Luis Palomino, a chemical and nano engineering Ph.D. candidate in Pokorski’s lab. “We developed the polymer in buffer conditions in water, allowing us to create a spray formulation that’s more biocompatible with plants.”
Using this modified method, the researchers produced a type of polymer material known as polynorbornene, which is permeable to gases. This permeability is crucial for allowing plant leaves to breathe and grow normally.
Testing and Results
The coating was applied to the leaves of Nicotiana benthamiana, a common plant model used in laboratory tests and plant molecular farming. It effectively protected live plants against Agrobacterium infection. When tested on individual leaves in petri dishes, the coating inhibited the growth of both Gram-negative and Gram-positive bacteria, such as Escherichia coli and Staphylococcus aureus.
A surprising discovery was that “full leaf coverage was not necessary to achieve protection,” noted Patrick Opdensteinen, a postdoctoral researcher in Steinmetz’s lab. “We can spray just a small part of the leaf, and that translates to bacterial immunity for the whole plant. That was a really cool outcome.”
“We can spray just a small part of the leaf, and that translates to bacterial immunity for the whole plant.” — Patrick Opdensteinen
Systemic Stress Response
The researchers suggest that this whole-plant protection may result from a systemic stress response. Treated leaves briefly exhibited a mild increase in hydrogen peroxide, a natural signaling molecule that plants produce in response to stress. This response diminished over time, and the plants remained healthy throughout the study. The team hypothesizes that this brief stress signal may activate a broader defensive response throughout the plant.
Enhancing Drought Tolerance
In addition to bacterial protection, the coated plants demonstrated improved drought tolerance. When water was withheld for four days, sprayed plants remained healthier and wilted less than untreated plants. The researchers propose that the polymer coating may act as a physical barrier to reduce water loss, while also inducing molecular-level stress response mechanisms that enhance drought resistance.
Future Research and Applications
Ongoing research will delve deeper into the mechanisms underlying both the whole-plant bacterial and drought resistance. The team will also focus on improving the coating’s biodegradability and assessing its toxicity for future agricultural applications.
“Our hope is to use this in the field to benefit agriculture, and this is the first step.” — Patrick Opdensteinen
This research was primarily supported by the National Science Foundation through the UC San Diego Materials Research Science and Engineering Center (UCSD MRSEC) DMR-2011924. The full study is titled “Polynorbornene Spray Coating to Enhance Plant Health.”
The development of this spray-on coating represents a promising step forward in the quest to protect crops from the dual threats of disease and drought, offering a potential boon to global agriculture and food security.
