Quinoa and similar highly stress-resistant plants have unique balloon-like structures on their surface called "bladders." For 127 years, it has been thought that these bladders help plants withstand drought and salty conditions. However, recent research from the University of Copenhagen overturns this theory. These so-called bladder cells actually have an entirely different and important function. The discovery makes it possible to breed more hardy quinoa plants, allowing for wider cultivation of this sustainable crop around the world.
Viewed through a microscope, it resembles a water balloon. Or a piece of glass art. But it's just a so-called bladder cell. If you're wondering what it's for, you wouldn't be the first. For 127 years, even the brightest experts in plant biology have thought that the fluid-filled bladders covering the leaves, flower clusters and stems of a range of hardy plants were nothing like what they look like today.
The discovery, thanks to a new study from the University of Copenhagen, goes completely against the researchers' expectations. This new discovery may be used to expand the cultivation range of this nutrient-rich, climate-resilient crop.
"Quinoa has been touted as a crop for the future because it is rich in protein and highly tolerant to drought and salt, as well as climate change. Scientists believe the secret to quinoa's drought resistance lies in the many epidermal bladder cells on the surface of the plant. Until now, it has been thought that the role of epidermal bladder cells is to store salt and water." Professor Michael Palmgren, from the Department of Plant and Environmental Sciences, said: "But this is not the case, and we have strong evidence for this."
A barrier against pests
Three years ago, a research team led by PhD student Max Moog and his supervisor Michael Palmgren began studying the epidermal bladder cells of the quinoa plant in an unprecedented way. They hope to understand how the plant resists salt and drought.
To do this, the researchers created mutant plants without bladder cells and compared their responses to salt and drought with wild quinoa plants filled with bladder cells.
The researchers were surprised to find that the bladder cells had no positive impact on the plant's ability to tolerate salt and drought. Instead, they appear to weaken tolerance. Instead, bladder cells act as a defense against pests and diseases.
"Whether we poured salt water on the mutant plants without bladder cells or exposed them to drought, they performed surprisingly well. So something was wrong. On the other hand, we could see that they were infested with large numbers of small insects -- unlike plants covered in bladder cells. That's when I realized that the bladder cells must have a completely different function," said Max Moog, now a postdoc in the Department of Plant and Environmental Sciences and first author of the study, published in the journal Current Biology.
When the researchers analyzed the material hidden inside the bladder cells, they didn't find the expected salt -- even though they added extra salt to the plants. Instead, they found compounds that repel the invaders.
"We found that bladder cells act as both a physical and chemical barrier against hungry pests. When tiny insects and mites trudge across a plant filled with bladder cells, they have no way of getting to the juicy green shoots that interest them most. Once they try to bite through the bladder cells, they find that the contents are poisonous to them," says Michael-Palmgren.
Quinoa's epidermal bladder cells contain oxalic acid, a compound also found in rhubarb that is a deadly poison to pests. Experiments have also shown that bladder cells even protect quinoa from one of the most common bacterial diseases in the plant, Pseudomonas syringae. This may be because bladder cells partially cover the stomata on plant leaves, which are entry points for many bacterial invaders.
"Our hypothesis is that these bladder cells are also resistant to other plant diseases, such as downy mildew, a fungal disease that severely limits quinoa yields," Max-Moog said.
The key to super-tolerant "super quinoa"
There are thousands of varieties of this South American crop, and the density of bladder cells on the plant's surface varies depending on the variety. But there's a lot of evidence that density determines how protective bladder cells are.
"It is likely that quinoa varieties with a higher density of bladder cells are more resistant to pests and diseases. On the other hand, they may be slightly less tolerant to salt and drought. And vice versa. These differences do not change the fact that quinoa is generally very salt- and drought-tolerant." Max-Moog continues: "But in addition to bladder cells, there must be The reasons have to be found elsewhere. As efforts are being made to expand quinoa cultivation around the world, the new knowledge could be used to adapt the crop to conditions in different regions. For example, southern Europe is very dry, while in northern Europe pests are a bigger problem than drought."
Michael Palmgren believes that the new results provide a specific method for how to cultivate "super quinoa" relatively easily:
"To date, these bladder cells have been overlooked in quinoa breeding. If you want a crop that is super resistant to pests and diseases, but also tolerant to salinity and drought, you can choose to breed varieties with dense coverage of bladder cells. So we may now have a tool to get a more tolerant 'super quinoa' through cross-breeding."
The findings add a new dimension to our understanding of quinoa. Until now, little is known about how the plant defends itself against attack by predators.
"Now we know that quinoa can withstand not only abiotic stresses such as drought and salinity, but also biotic impacts such as pests and pathogenic bacteria. At the same time, we have also discovered the secret of these strange-looking bladder cells." The professor concluded: "This study is an example of how established facts are not always true."
Compiled source: ScitechDaily