Mapping the use of nitrogen during photosynthesis

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Ask a farmer to name the most essential components for crop production and without doubt, nitrogen will be first on the list. Now Australian researchers have created a map of how nitrogen is used during photosynthesis in wheat, rice and maize, the three main cereal crops that global security depends on.

“We know that improving photosynthesis has enormous possibilities to increase yields, and we also know that nitrogen is central to this process. Our review follows the roads nitrogen takes inside the plant, from fertiliser to grain,” said lead researcher Professor John Evans from the ARC Centre of Excellence for Translational Photosynthesis.

Farmers commonly apply nitrogen fertilisers at levels in excess of what the plant needs, to ensure a protein rich grain. The problem is that over fertilising is not only expensive, but has many side effects in the environment such as contamination of ground water, algae blooms, contribution to greenhouse emissions and infertility of livestock.

“Fertilisers are applied because plants need nitrogen to grow and to replace the nutrients removed in the harvested product. We need to know exactly where and how nitrogen is used by the plant. This information will help us to target specific proteins and enzymes and in the future, make plants more efficient at using nitrogen,” Professor Evans said.

The study, published recently in the Journal of Experimental Botany, explored the consequences of changing the nitrogen budget in many of the proteins involved in photosynthesis, the process by which plants transform carbon dioxide into grains, leaves and stems using the energy of the Sun.

ANU researcher and co-author Dr Tory Clarke said most of the proteins involved in photosynthesis don’t require much nitrogen, but there are big nitrogen spenders like Rubisco, the main enzyme in charge of fixing carbon during photosynthesis.

“Our Centre is working on different targets towards making crops more productive by improving photosynthesis, but you can’t just make photosynthesis faster, and by doing so creating more carbon in relation to nitrogen content, because that decreases the quality of the grain,” said Dr Clarke from the Research School of Biology and the ARC Centre of Excellence for Translational Photosynthesis at ANU.

“We need to balance how the plant is managing both nitrogen and carbon resources, and this map is like a checkpoint that allows us to keep an eye on the cost of nitrogen during photosynthesis.”

 This work was funded by the Australian Research Council (ARC) Centre of Excellence for Translational Photosynthesis (CoETP) at the lead node located at ANU.

Read full paper here