Abstract
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.
Highlights
Fertilisation is a prerequisite to meet high yields and optimum quality of crops
Several plant species treated with low concentrations of ammonium as sole nitrogen source did not grow as well as when they are supplied with the same concentration of nitrate or ammonium combined to nitrate [13, 14]
Our results are in agreement with the results obtained by El Omari et al, and Robin et al, [21, 23], who found a clear relationship between the concentration of nitrate and nitrate reductase activity in sorghum roots
Summary
Fertilisation is a prerequisite to meet high yields and optimum quality of crops. Unlike most of mineral elements essential to plant development and which are needed in trace amounts, some key elements like nitrogen (N), phosphorus (P) and potassium (K) are needed in large amounts, these elements are frequently in short supply in the soil to allow optimal growth of crops. Nitrate (NO3--N) and ammonium (NH4+-N) are the major forms of nitrogen that plants use for growth and development These two forms of inorganic nitrogen are absorbed by specific transport systems in roots. The enzyme fulfils essential non-photosynthetic functions the anaplerotic replenishment of tricarboxylic acid cycle intermediates for biosynthetic purposes and nitrogen assimilation [5]. This anaplerotic role makes this enzyme an ideal choice to study interaction between carbon and nitrogen metabolism. In this study we tried to contribute to the understanding of this interaction between carbon and nitrogen metabolism using a Moroccan sorghum ecotype and focusing on some enzymes activities like PEPC, NR, GS, and AAT
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