Biological complexity: how plants bind nitrogen (Introduction)

by David Turell , Wednesday, January 29, 2020, 21:05 (1546 days ago) @ David Turell

Another way using bacteria and altered flavonoids:

https://phys.org/news/2020-01-scientists-soil-environment-cheap-steady.html

"Researchers in Rice University's Systems, Synthetic and Physical Biology program detailed how plants have evolved to call for nutrients, using convenient bacteria as a delivery service.

"Their open-access report in Science Advances looks at how plants read the local environment and, when necessary, make and release molecules called flavonoids. These molecules attract microbes that infect the plants and form nitrogen nodules—where food is generated—at their roots.

"When nitrogen is present and available, plants don't need to order in. Their ability to sense the presence of a nearby slow-release nitrogen source, organic carbon, is the key.

"'It's a gorgeous example of evolution: Plants change a couple of (oxygen/hydrogen) groups here and there in the flavonoid, and this allows them to use soil conditions to control which microbes they talk to," said Rice biogeochemist Caroline Masiello, a co-author of the study.

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"Plants use flavonoids as a defense mechanism against root pathogens and could manipulate the organic carbon they produce to interfere with signaling between microbes and other plants that compete for the same nutrients.

"Overall, they showed that higher organic carbon levels in soil repressed flavonoid signals by up to 98%. In one set of experiments, interrupting the signals between legume plants and microbes sharply cut the formation of nitrogen nodules.

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"They found the most dramatic effects when dissolved carbons derived from plant matter or compost were present. Plants employ naringenin, a variant of the flavonoid that gives grapefruit its bitter taste, and luteolin, expressed by leaves and many vegetables, to call for microbial nitrogen fixation. These were most curtailed in their ability to find microbes. Quercetin, also found in foods like kale and red onions and used for defense against pests, did not suffer the same fate.

"Masiello noted there's a cost for plants to connect with microbes in the soil.
"These relationships with symbionts are metabolically costly," she said. "Plants have to pay the microbes in photosynthesized sugar, and in exchange the microbes mine the soil for nutrients. Microbial symbionts can be really expensive subcontractors, sometimes taking a significant fraction of a plant's photosynthate.

"'What Ilenne and Tara have shown is one mechanism through which plants can control whether they invest in expensive symbionts," she said. "Among a wide class of signaling compounds used by plants for many purposes, one specific signal related to nutrients is shut off by high soil organic matter, which is a slow-release source of nutrients. The plant signal that says 'come live with us' doesn't get through.

"'This is good for plants because it means they don't waste photosynthate supporting microbial help they don't need. Ilenne and Tara have also shown that signals used for other purposes are slightly chemically modified so their transmission is not affected at the same rate.'"

Comment: this three-way arrangement depends upon carbon availability, plant responses and soil bacteria. So complex I wounder if it possibly evolve by chance, Since it involves figuratively juggling three balls in the air, I would think it was designed.