Green is a colour almost universally associated with plants, and for good reason. The green pigment chlorophyll is essential to plants’ ability to generate food, but what happens if they don’t have enough?
New work from Carnegie, Michigan State University, and the National Research Institute for Agriculture, Food and Environment in France reveals the complex, interdependent nutrient responses underpinning a potentially deadly, low-chlorophyll state called chlorosis that’s associated with an anemic, yellow appearance.
Their findings could usher in more environmentally friendly agricultural practices using less fertilizer and fewer water resources.
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Photosynthesis is the complex biochemical process by which plant cells convert the sun’s energy into chemical energy, which then is used to fix carbon dioxide from the atmosphere into sugar molecules. It occurs inside highly specialized plant cell organelles called chloroplasts.
Nutrients accumulate in chloroplasts and are essential to optimal function. The research team, led by MSU’s Hatem Rouached and including Carnegie’s Sue Rhee, Hye-In Nam, Yanniv Dorone, Sophie Clowez and Kangmei Zhao, showed that a balance of iron and phosphorus are necessary to prevent chlorosis.
“For a long time, experts have thought that low iron is the sole cause of chlorosis and farmers have often applied iron to combat leaf yellowing,” Rhee said. “But recent work has shown that other nutrients play a role in bringing about this anemic reaction.”
To better understand what makes leaves chlorotic, the investigators looked at the response to multiple nutrients in concert, rather than one by one.
They found that plants showing chlorosis induced by iron deficiency would yellow and photosynthetic activity would be affected, as expected. However, when the nutrient phosphorus was also removed, the plant’s leaves started accumulating chlorophyll and turned green again.
The explanation for this unexpected response lies in the signaling between the chloroplast, where photosynthesis occurs, and the cell’s nucleus, where its genetic code is stored.
Interdisciplinary analyses indicated the nucleus’ ability to regulate gene expression in response to low iron depends on the availability of phosphorus. This kind of complex layering of nutrient responses shows there is much still to learn about communication channels between these two crucial plant organelles.
The team’s findings could have implications for resilience in food crops, especially crucial in a changing climate.
“We need to rethink fertilizer management, for example,” Rouached said. “If we take actions that don’t consider how the nutrients interact with each other, we potentially create conditions that set plants up to fail. It’s critical that we correct this thinking moving forward for the benefit of food production worldwide.”
