To ensure their nutrition, plants absorb mineral ions (nitrate, potassium, phosphate, iron, etc.) from the soil via their roots. This phenomenon is complicated by the fact that these ions are generally only available at low levels, but these can also can vary in time and space. To overcome these constraints, the roots grow constantly in order to explore new areas of soil and thus search for these mineral ions. However, this growth is not random, but on the contrary is carefully guided by molecular mechanisms that enable the roots to localise zones in the soil containing high levels of mineral ions, where they develop preferentially.
The INRA research team in Montpellier has identified one of these mechanisms relative to a major mineral, nitrate, which is the main source of nitrogen for plants. This mechanism involves a specific protein, NRT1.1, which has the unique characteristic of being both a membrane transporter to enable the entry of nitrate in the root cells, and a nitrate "sensor" that can stimulate the growth of roots in areas where this ion is present. Thus, in a highly original manner, NRT1.1 governs the development of roots because it is also involved in transporting a plant growth hormone, auxin. When nitrate is abundant in the environment, NRT1.1 directs auxin transport to the tissues in such a way that the hormone accumulates in the roots (see photo), thus accelerating their growth.
All living beings are endowed with systems that regulate their physiology or development through nutrient "sensors". The mechanism described here is novel because it helps us to understand how one of these "sensors" can combine the detection of a nutrient with the hormonal control of plant development. This research opens new paths towards improvements in the use of fertilisers by farmers. Indeed, nitrate is one of the main components in these fertilisers, and the amount that is not taken up by crops causes the pollution of ground and surface water. In this context, discovery of the mechanisms implemented naturally by plants to optimise their nitrate uptake is of importance. It may help to breed varieties that are more efficient in their use of nitrate fertilisers, and hence crops that are more environmentally-friendly.
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| Without Nitrate With Nitrate |
Young secondary roots of wild arabis (Arabidopsis thaliana), supplied or not with nitrate. If no nitrate is present in the environment, there is no auxin in the roots. When nitrate is added, an accumulation of auxin can be seen (blue staining), thus enabling the roots to grow specifically towards the source of nitrate in the soil and not elsewhere.
Reference:
Nitrate-regulated auxin transport by NRT1.1 defines a mechanism for nutrient sensing in plants. Developmental Cell 18 : 927-937
Gabriel Krouk1,5, Benoît Lacombe1, Agnieszka Bielach2, Francine Perrine-Walker1, Katerina Malinska3, Emmanuelle Mounier1, Klara Hoyerova3, Pascal Tillard1, Sarah Leon1, Karin Ljung4, Eva Zazimalova3, Eva Benkova3, Philippe Nacry1 and Alain Gojon1.
1Biochimie et physiologie moléculaire des plantes, UMR 5004 CNRS/INRA/SupAgro-M/UM2, Institut de Biologie intégrative des plantes, Place Viala, 34060 Montpellier Cedex 1, France.
2Flanders Institute for Biotechnology, Department of plant systems biology, Ghent University, Technologiepark 927, 9052 Ghent, Belgium.
3Institute of experimental botany, Academy of sciences of the Czech Republic, Rozvojova 263, 16502 Prague 6, Czech Republic
4Umea Plant Science Center, Department of Forest genetics and plant physiology, Swedish university of agricultural sciences, SE-901 83 Umea, Sweden
5Present address: Department of Biology, New York University, 100 Washington Square East, New York, NY 10003, USA
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