Wetland plants have a high tolerance to flooding due to the formation of “aerenchyma lysigenes”, air channels that help transfer gases to submerged roots. These channels also help the plant resist drought and nutrient deficiencies. Now, Japanese scientists are studying the underlying mechanism of aerenchyma formation to better understand the phenomenon, paving the way for the development of crops resistant to extreme climate change.
Floods and droughts are the major environmental disasters responsible for most crop failures. Aerenchyma formation can help crops cope with these environmental stresses. However, it is not commonly seen in non-wet species like wheat and maize, which are staple food crops in some parts of the world. Researchers Takaki Yamauchi and Mikio Nakazono from Nagoya University, Japan, reviewed the literature on the subject to get some concrete insight into the various factors involved in the formation of aerenchyma. “If we can genetically control the timing and amount of aerenchyma lysogen formation in the roots of all agronomically important crops, such as corn, wheat, and soybeans, the loss of global agricultural production could be significantly reduced,” says Dr. Nakazono.
Dr. Yamauchi and Dr. Nakazono suggest imagining aerenchyma lysogen to a snorkel used to breathe underwater. During flooding, roots are cut off from oxygen and other vital gases necessary for survival. In response, the plant creates airways connecting the submerged regions of the plant to the parts above water. Similar to a snorkel, these pathways help the plant “breathe” by transporting gases to submerged roots. Additionally, air channels reduce energy requirements for the respiration process and can help the plant conserve energy under extreme drought or nutrient deficit conditions.
The researchers found that a phytohormone called “auxin” is required for aerenchyma formation during normal root growth and identified two factors leading to the induction of aerenchyma formation in response to flooding. The phenomenon begins when the roots are submerged under water under aerobic conditions. Restrictions on gas exchange cause the accumulation of ethylene in the roots, which encourages the production of respiratory oxidase (RBOH) homologue – an enzyme responsible for the production of reactive oxygen species (ROS) . It turns out that the released ROS trigger cell death in the tissues, forming cavities for the passage of gases.
RBOH can also be activated by the presence of calcium (Ca2+) ions that are transported from the apoplast (water pathways). Some plants have calcium-dependent protein kinases that utilize Ca2+ to add phosphates to RBOH, stimulating it to produce ROS. This effect occurs at later stages when plants gradually experience oxygen starved conditions after prolonged underwater submersion.
While aerenchyma is primarily associated with plants that have adapted to soils with high water content, it can also develop in upland plants in drought and nutrient deficiency conditions. Low concentrations of nitrogen and phosphorus, essential nutrients needed for plant growth, have been shown to increase sensitivity to ethylene, stimulating aerenchyma formation. Additionally, ethylene was also a common factor in triggering corn aerenchyma, providing a means to improve crop resilience. “Increased ethylene sensitivity could be an effective strategy to stimulate aerenchyma formation in the absence of gas-restricted diffusion,” Dr. Yamauchi speculates.
While the mechanism behind the formation of aerenchyma remains unclear, suggesting the need for further research, the results of this study open up the possibility of improving crop resilience and paving the way for better food security in the wake of climate change.
The new document is based on the following two documents:
“Fine control of aerenchyma and lateral root development through AUX/IAA and ARF-dependent auxin signaling.” Proceedings of the National Academy of Sciences of the United States of America116, 2019, DOI: 10.1073/pnas.1907181116
“A NADPH oxidase RBOH functions in rice roots during the formation of lysogenic aerenchyma under oxygen-deficient conditions.” The plant cell29, 2017, DOI: 10.1105/tpc.16.00976
This study was supported by the Japan Science and Technology Agency PRESTO grant JPMJPR17Q8 to TY and Grant-in-Aid for Transformative Research Areas (A) (MEXT KAKENHI grant JP20H05912) to MN