A new study from the University of Kentucky’s Martin-Gatton College of Agriculture, Food and Environment is shedding light on how plants can lose the ability to communicate disease warnings across their tissues, a finding that could have implications for crop breeding and disease resistance.
Published in "Science Advances", the research examined how excess nitric oxide can interfere with systemic acquired resistance, or SAR, a whole-plant immune response that allows plants to prepare for future pathogen attacks after an initial infection.
Unlike animals, plants do not have blood, nerves or immune cells. Instead, they rely on chemical signaling to coordinate defense responses. When one leaf is infected, warning signals travel to other parts of the plant, allowing unaffected tissues to activate protective measures.
The study found that this system can fail when nitric oxide, a molecule involved in plant growth, stress responses and disease defense, accumulates at high levels.
Researchers used Arabidopsis, a model plant commonly studied in laboratories, focusing on plants with a mutation in the GSNOR1 gene. The gene, conserved in both plants and humans, helps regulate nitric oxide levels. Plants with the mutation accumulated excess nitric oxide and showed weakened systemic immunity.
Central to the SAR process is salicylic acid, a signaling molecule that carries immune alerts from infected tissues to the rest of the plant. The study showed that elevated nitric oxide altered the pH balance inside and outside plant cells, disrupting the movement of salicylic acid.
In affected plants, the area outside the cell became more acidic while the inside became more alkaline. That imbalance created conditions that restricted salicylic acid from entering the plant’s transport system, effectively blocking the immune signal from reaching distant tissues.
Researchers also tested whether alternative delivery methods could restore immune responses. When salicylic acid was sprayed directly onto leaves, the mutant plants still showed limited immune activation. But when the compound was delivered through the roots, immune signaling and SAR were restored.
The results suggest the plant’s immune machinery remained functional, but the signal could not move effectively through the normal transport pathway.
For plant breeders and seed developers, the findings offer new insight into how internal signaling pathways influence disease resistance. Understanding how molecules such as nitric oxide regulate the movement of defense signals could help researchers develop crops with stronger resilience against pathogens and environmental stress.
The study also points to broader biological significance. Because nitric oxide plays a role in signaling and transport in animals as well as plants, researchers said the work may help reveal common principles of chemical communication across living systems.
Source: University of Kentucky Martin-Gatton College of Agriculture, Food and Environment, "UK researchers find excess nitric oxide blocks plant immune signals "