Nitrogen assimilation under different nitrate nutrition in Tunisian durum wheat landraces and improved genotypes

Abstract

The effects of nitrate were studied in wheat varieties grown in hydroponic culture: two landraces (Azizi and Bidi), and two improved genotypes (Om Rabiaa and Khiar) from Tunisia. Nitrogen (N) supply generally induced an increase in plant height in all varieties, albeit to a different extent; interestingly, landraces exhibited the same N Uptake Efficiency (NUpE) as other varieties, and a lower Nitrogen Utilization Efficiency (NUtE); in contrast, improved genotypes exhibit a better NUtE at high N. Nitrate reductase activity (NRA) was sensibly and constitutively higher in the improved genotypes in the roots, while NRA was strongly influenced by nitrate supply in the leaves of Bidi landrace. Glutamine synthetase (GS) activity was similar in all varieties studied, in contrast, ferredoxin-glutamate synthase (Fd- GOGAT) activity and occurrence were increased by nitrate. Intriguingly, glutamate dehydrogenase (GDH) activity followed an opposite behaviour with respect to GOGAT. Glucose-6P-dehydrogenase (G6PDH), which provides reductants for N assimilation, increased in roots upon nitrate supply, but the different plastidial and cytosolic isoforms differently changed in the different varieties studied. The data suggest that landraces present higher metabolic flexibility as compared with improved cultivars; therefore, the metabolic changes observed could be suitable for the identification of factors limiting the NUtE.

Keywords:

• Nitrogen metabolism
• nitrogen use efficiency
• glutamate synthase
• glucose-6-phosphade dehydrogenase
• Triticum varieties

Acknowledgements

The authors would like to thank A. von Schaewen (Univ. of Münster, Germany) and A. Marquez (Univ. of Sevilla, Spain) for the generous gift of potato G6PDH antisera and barley Fd-GOGAT antibodies, respectively.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by grants from the Tunisian Ministry of Agriculture and the Tunisian Ministry of Higher Education, Scientific Research and Information and Communication Technologies. Manuela Cardi acknowledges Project FORGIARE (FORmazione GIovAni alla RicErca) V - 10/FORG/ST/2012/5 by Compagnia di San Paolo. Giorgia Capasso acknowledges Project “Garanzia Giovani” 2018 by Regione Campania.