For many years, researchers have wondered about the function of some small fluid-filled bladders on quinoa plants, but that mystery has now finally been solved. The bladders have a different function than researchers thought.
The surfaces of the leaves of a quinoa plant are covered with many small fluid-filled bladders that almost look like morning dew.
However, new research now shows the function of these bladders.
For many years, researchers thought that the bladders help the quinoa plant to tolerate drought or excrete excess salt, but the bladders actually protect the plants against insects and other pests (arthropod herbivores).
According to a researcher behind the discovery, this discovery is important because people will probably eat a lot more quinoa in the future.
“Quinoa is very hardy and is therefore useful as a future crop in a changing climate. Our research shows that breeding quinoa requires close attention to the bladder cells on the surface of the leaves, because they help to protect the plant from insects and other pests. One idea involves breeding plants with even more bladder cells, since they will probably be even better protected,” explains Michael Palmgren, Professor at the University of Copenhagen’s Department of Plant and Environmental Science.
The research has been published in Current Biology.
Some plants are extremely salt- and drought-tolerant
The researchers aimed to confirm what other researchers had suspected: that the bladder cells help the quinoa plant to be more resistant to drought or salt.
Several other plants have bladder cells on their surface, and many of these plants grow in very harsh environments.
This applies to the ice plant from Namibia and saltbush, which both grow by the seashore, and quinoa, which originates from barren areas high up in the Andes.
All these sites have very little rainfall and a high concentration of salt, and researchers had hypothesised that the fluid-filled bladders were a water reservoir or that the plants used them to expel salt.
“We were sure that one of these two scenarios must apply. But sometimes the research takes twists and turns that you just have to follow,” says Michael Palmgren.
Other researchers did not trust the results
The researchers exposed quinoa seeds to chemicals that induce many mutations.
They then sowed the seeds in a field and looked among the sprouts for quinoa plants without bladder cells and grew them under extremely controlled conditions in the laboratory.
This enabled them to investigate whether lacking the bladder cells affects the plant’s ability to grow in very dry or very salty environments.
Both studies showed that quinoa plants without bladder cells do not grow smaller or perform worse than wild-type plants with bladder cells. If anything, the mutant plants in the experiment actually did better in drought conditions than the wild type.
“We published these results last year, but we had difficulty because other researchers did not really believe the results, since we disproved everything that other researchers thought,” explains Michael Palmgren.
Insects cannot penetrate the bladder cells
When the experiments in the growth chambers became so extensive that the researchers no longer had room for the plants, they decided to grow some mutant quinoa in a greenhouse, where the conditions are not as easy to control.
To their surprise, they noticed that the mutant plants had much poorer growth than the wild type.
They became curled and the top shoots died.
The researchers examined the plants more closely and found that the top shoots of the mutant plants without bladder cells had many thunder flies, which are small insects that are problematic pests in greenhouses.
They then investigated whether wild-type quinoa and mutant quinoa differ in being invaded by insects and other pests.
This part of the study showed that spider mites, butterfly larvae and thunder flies can much more easily settle in and feed on quinoa without bladder cells.
Michael Palmgren explains that the number of bladder cells on a quinoa leaf does not change over time, which means that a top shoot is completely covered with bladder cells from the start. Over time, as the leaf grows, the bladder cells are distributed over the leaf and are more spread out.
“But the bladder cells are so dense on the top shoots that they create a physical barrier that insects and other small pests cannot get through. This protects the quinoa plant and is the function of the bladder cells,” he adds.
Bladder cells contain oxalic acid
The researchers also examined the liquid in the bladder cells and found that it contains large quantities of oxalic acid, which is also present in rhubarb and other plants and is known to be toxic to insects.
The researchers tested oxalic acid on the spider mites, and they died.
Thus, the bladder cells not only provide physical protection by forming a barrier around the fresh leaves but also a chemical barrier.
According to Michael Palmgren, the result is interesting because in breeding quinoa plants, researchers have never thought of specifically seeking plants with many bladder cells.
However, they should do this, since these plants will be better protected from insects, while quinoa also has a unique ability to resist drought and salt, which will be useful as the world’s climate changes.
“The quinoa plant can do a little bit of everything. It is well protected against drought, salt and pests. Now we have discovered how its protection mechanism against pests, but this also means that we do not know how it protects itself against drought and salt. We are back to square one, so now we will try to solve that mystery by using other methods,” concludes Michael Palmgren.
