Effect of Nitrogen Source and Concentration on Growth and Activity of Nitrogen Assimilation Enzymes in Roots of a Moroccan Sorghum Ecotype

Carbon and nitrogen metabolism pathways are regulated by complex mechanisms in order to optimize growth and development of plants. This study was conducted to contribute to the determination of roles of some key enzymes of carbon and nitrogen metabolism in sorghum roots. Sorghum were grown under nitrate (NO3-), ammonium (NH 4+) or nitrate combined to ammonium at different concentrations. Growth parameters and protein content were evaluated. In addition, we analyzed key enzymes activities involved in nitrogen and carbon metabolism such as: nitrate reductase (NR), glutamine synthetase (GS), aspartate aminotransferase (AAT) and phosphoenolpyruvate carboxylase (PEPC). At high nitrogen levels (ammonium or nitrate), the sorghum roots showed an increase in biomass accompanied by an increase in protein content. Likewise, high concentrations induced accumulation of the non-photosynthetic isoform of phosphoenolpyruvate carboxylase. Glutamine synthetase and aspartate aminotransferase activities were also increased, especially at high levels of ammonium. These results showed that sorghum plants have an efficient system for nitrogen assimilation in their roots, allowing this plant to tolerate excessive concentration of this nutrient.