‘Lysigenous aerenchyma’ acts like a snorkel, researchers say, transferring air and nutrients to plant roots submerged underwater or suffering from drought.
Researchers Takaki Yamauchi and Mikio Nakazano are looking into a ‘snorkel’-like formation in plant roots, a news release says, hoping to develop crops that can withstand extreme weather events such as flooding and droughts.
Aerenchyma is “porous root tissue, especially well developed in wetland plants,” that allows oxygen and other gases to make it to the roots from the tips of the plant, according to the Encyclopedia of Biodiversity. “This tissue supports the respiratory demand of the root tissues and allows oxygen to leak into the surrounding soil.”
The Japanese scientists note in a news release that with the help of air channels that transfer gases to the submerged roots, “wetland plants have a high tolerance against flooding.” They add that “These channels also help the plant withstand drought and nutrient deficiency.”
“If we can genetically control the timing and amount of ‘lysigenous aerenchyma’ formation in roots of all agronomically important crops, such as maize, wheat and soybean, the global crop production loss could be dramatically reduced,” says Dr Nakazono.
Plants that are raised in wetlands can withstand environmental stresses, better than non-wetland species such as wheat and maize – which help feed a big portion of the world.
Yamauchi and Nakazano, both from Japan’s Nagoya University, have gone over literature on the topic to get a better understanding of the various factors leading to aerenchyma formation, writing a paper published in Trends in Plant Science late last year.
Comparing the phenomenon of lysigenous aerenchyma to a snorkel, the researchers suggest that it can be used by a plant to breathe underwater. When the fields are submerged by water during flooding, the roots cannot get enough oxygen and other vital gases they need to survive.
Just as a snorkel helps a diver in the sea, lysigenous aerenchyma pathways help the plant breathe by carrying gases from over the water to the roots under the water. What’s more, the air channels lessen the need for energy for the breathing process and can help the crop conserve energy during extreme conditions.
The researchers discovered that the formation of aerenchyma during normal root growth is dependent on a phytohormone called ‘auxin’. When the roots of the plant are flooded in aerobic conditions, ethylene accumulates in the roots. That ends up causing the production of RBOH (respiratory burst oxidase homolog) – an enzyme, the news release notes, that is responsible for reactive oxygen species (ROS) production. ROS, when released, kills cells in tissues, forming cavities that allow the plant to ‘breathe’ underground even when submerged under water.
Aerenchyma is mostly seen in plants that grow in soils that are soaked with water, but it can also develop in plants that are suffering from drought and nutrient deficiency. In plants that have low concentrations of nitrogen and phosphorus, ethylene sensitivity is increased, leading to the formation of aerenchyma.
Ethylene also helped trigger aerenchyma in maize (corn), according to the news release, helping the crop become more resilient to drought or flooding.
“The increase in ethylene sensitivity could be an effective strategy to stimulate aerenchyma formation in the absence of restricted gas diffusion,” speculates Dr Yamauchi.
The researchers do not pinpoint the exact mechanism behind aerenchyma formation and comment that further research is necessary. Yet the findings suggest ways to improve crop resilience and support farmers and populations dependent on their crops, helping to ensure better food security.