image: (Left) Wheat grown at normal temperature. (Right) Wheat grown at moderately higher than normal temperatures. This wheat showed high levels of iron deficiency, yellower leaves, less photosynthesis, and growth was stunted.
Credit: RIKEN
Researchers led by Keiichi Mochida at the RIKEN Center for Sustainable Resource Science (CSRS) in Japan have discovered that extended periods of high stress lead to iron deficiency and stunted growth in wheat crops. Experiments show reducing iron deficiency with a synthetic organic molecule called PDMA results in better growth and healthier plants. These findings are good news for farmers and consumers alike and could lead to treatments in the field that improve wheat production during prolonged periods of heat. The study was published in the scientific journal Nature Communications.
One of the biggest fears of ongoing climate change is that extended periods of heat will disrupt food production. Even moderate warming can reduce the yield of cool-season cereal crops such as wheat, with one global study estimating that wheat production declines by 6% for every increase of one degree Celsius. Not only do these crops do less photosynthesis and produce smaller kernels of grain, but the grain is also less nutritious. While most research into how plants adapt to heat stress has focused on acute stress—very high temperatures over a few days—Mochida and his team reasoned that the bigger threat posed by climate change is extended periods of moderately high temperatures.
The researchers characterized what happens to bread wheat after two weeks of moderate heat stress. Compared to wheat grown at normal temperatures, the stressed out wheat plants weighed less and analysis indicated they were doing less photosynthesis. When checking for nutrient deficiencies, the researchers discovered that the leaves from the heat-stressed plants contained less than half the normal amount of iron. Could their stunted growth be the result of iron deficiency?
Genetically, wheat is complex. To get down to the biological details, the researchers turned to a genetically simpler grass called purple false brome (Brachypodium distachyon), which is often used as a model plant for studies of cereal crops. Typically, model plants for experiments come from biobanks that store specific specimens that can then be used by researchers around the world, ensuring consistent genetics every time. For a widely used model like B. distachyon, biobanks contain numerous individual samples, each with a code name and its own slightly different genetics, just like people.
In experiments, the model grass responded to heat stress in almost the same way the wheat had. But the degree to which the grass was affected varied sample by sample, as did the iron deficiency. For example, grass sample Bd21 had extremely low biomass, very yellow leaves, and 91% less iron than plants grown in normal temperatures. On the other hand, sample Bd21-3 had somewhat milder symptoms and only 61% iron deficiency. With the simpler genome, the researchers were able to compare these two model grass samples and pinpoint BdTOM1, the gene responsible for the difference.
Plants cannot extract iron from the soil as is. Instead, they make organic compounds called mugineic acids and dump them in the soil. Once these compounds bind to iron in the soil, the plants can then take it up through their roots. The gene BdTOM1 is responsible for making the mugineic acids. Analysis showed that after two weeks of heat stress, grass sample Bd21-3 had a lot more deoxymugineic acid in its roots than did Bd21, explaining why Bd21 had greater iron deficiency and indicating that variations in BdTOM1 likely lead to variations is heat-stress susceptibility.
The researchers then reasoned that they could alleviate iron deficiency and improve growth by giving heat-sensitive plants more deoxymugineic acid. They tested this hypothesis in the model grass and in wheat using a synthetic deoxymugineic acid called PDMA. Their hypothesis was correct; under heat stress, PDMA treatment led to improved photosynthesis and biomass, provided the PDMA concentration wasn't too high.
Mochida is optimistic about seeing these findings tested in the field. “In the short term,” he says, “this research proposes a new approach to enhancing crop heat stress tolerance, demonstrating the potential to optimize iron uptake and improve agricultural productivity.”
“In the long term, breeding efforts targeting genes involved in nutrient homeostasis could contribute to food security and sustainable agriculture, considering climate scenarios, societal needs, and resource competition across sectors such as agriculture and energy.”
Journal
Nature Communications