Scientists Discover Why Critical Plant Defense Signals Fail to Reach Healthy Tissues.
Researchers at the University of Kentucky’s Martin-Gatton College of Agriculture, Food and Environment have uncovered new details about how plant immune systems can break down when critical internal signals fail to move throughout the plant.
Unlike animals, plants do not have immune cells, blood circulation, or nervous systems. Instead, they rely on chemical messengers that help coordinate defense responses.
When one part of a plant is attacked by disease, warning signals are sent to healthy tissues, allowing them to prepare for potential threats.
The new study, published in Science Advances under the title “Excess nitric oxide alters cellular pH to restrict salicylic acid movement and systemic immunity,” examined how elevated levels of nitric oxide interfere with this process.
Nitric oxide is a naturally produced molecule that plays an important role in plant growth, stress adaptation, and immunity. However, researchers found that excessive amounts can hinder the plant’s ability to defend itself.
Using Arabidopsis plants carrying a mutation in the GSNOR1 gene, scientists observed weakened systemic acquired resistance (SAR), a mechanism that helps plants develop protection throughout their tissues after an infection occurs.
The research focused on salicylic acid, a key immune-signaling compound that helps spread defense messages. As Huazhen Liu, first author of the study, explained, “Systemic immunity is like plant memory,” said Huazhen Liu, first author of the work.
“After one leaf survives an attack, the plant needs to warn the rest of its body. Salicylic acid helps carry that alert signal.”
The team discovered that excess nitric oxide altered the pH balance inside and outside plant cells. This created conditions that prevented salicylic acid from moving effectively through the plant.
“When nitric oxide levels become too high or uneven, they change the acidity around the cell,” Liu said. “That creates a barrier for salicylic acid. The signal gets trapped, and the rest of the plant does not get the warning.”
The findings emphasize that successful disease resistance depends not only on producing signals but also on ensuring they can travel where they are needed.
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