Plants, like people, know when they are full — and scientists have now found the molecular signal that tells a plant to stop eating. A team led by New York University and Argentina's INGEBI research institute has identified a protein called HHO5 that acts as the plant's 'nitrogen satiety' switch, according to a study published in The Plant Cell.
Nitrogen is the nutrient that most limits crop growth, and the world's farms apply enormous amounts of it as fertilizer. But plants only absorb around half of what is applied. The rest leaches into waterways, feeding harmful algal blooms, or lingers in the soil where it contributes to emissions of nitrous oxide — a greenhouse gas about 273 times more potent than CO2 over a century. Producing and shipping fertilizer is also costly and politically fragile.
The NYU team found that when a plant has built up enough organic nitrogen, HHO5 kicks in with a two-part message: it switches on genes that process the nitrogen already stored, while switching off the genes that pull more inorganic nitrogen out of the soil — in effect saying, 'I'm full.' When HHO5 teams up with a partner protein called WRKY21, it changes roles and becomes an activator of organic-nitrogen genes.
To prove the switch really controls appetite, the researchers created Arabidopsis plants lacking HHO5. In specific nitrogen conditions, those plants absorbed nearly three times more nitrogen than normal ones. 'This knowledge may aid the engineering of gluttonous plant varieties that absorb more available nitrogen,' said Will Hinckley, the study's lead author.
Growing crops that eat more of the nitrogen they are given — or need less of it — could shrink fertilizer bills, protect waterways, and cut agricultural greenhouse gas emissions. NYU has filed a patent application covering the findings.
