Tolerance to ammonium nutrition in plants can be related to their ability to detoxify ammonium via nitrogen assimilation in roots. Here, we report that sorghum-sudangrass (Sorghum bicolor L. Â S. bicolor var. sudanense) hybrids exhibited enhanced biomass production under high levels of inorganic nitrogen supply as well as increased capacity for nitrogen assimilation in roots. Glutamine synthetase (GS, EC 6.3.1.2) activity and protein accumulated in roots at increasing concentrations of either nitrate or ammonium, with particularly high levels of GS in ammonium-treated plants. Ammonium but not nitrate differentially regulated two distinct cytosolic GS (GS1) isoforms composed by polypeptides of similar size but different charge. The comparative analysis of GS gene sequences and the deduced GS1 polypeptides suggested that the two GS1 isoforms were the expression products of SbGln1.2 and SbGln1.3 genes. SbGln1.3 expression was shown to be upregulated by high levels of inorganic nitrogen supply, with a maximal abundance of SbGln1.3 transcripts in ammonium-grown plants. SbGln1.2 expression was uniform along the root axis meanwhile protein and transcript levels for SbGln1.3 were particularly abundant in the upper part of the axis where lateral roots are prominent. Kinetic analysis revealed that the two GS1 isoenzymes have relatively low-affinity for ammonium ions. The spatial distribution of low-affinity GS1 isoenzymes would provide a sustained glutamine biosynthesis at high levels of ammonium supply and may represent at the same time an efficient system of ammonium detoxification. Such a mechanism may prevent transport of ammonium to leaves alleviating symptoms of toxicity and therefore contributing to sorghum ammonium tolerance.

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Sorghum, the fifth most important cereal crop, is a well-adapted cereal to arid/semi-arid regions. Sorghum is known for multiple end-uses as food, feed, fuel, forage, and as source of bioactive compounds that could be used for medical applications. Although the great improvement in the process of sorghum breeding, the average yield of this crop is still very low. Therefore, exploring the genetic diversity in sorghum accessions is a critical step for improving this crop. The main objective of the current work was to study the genetic variation existing in a Moroccan sorghum collection. Indeed, 10 sorghum ecotypes were characterized based on agromorphological descriptors. Both quantitative (25) and qualitative (7) traits revealed variability (p < 0.05) among the studied ecotypes. At the seedling stage, most of the ecotypes showed good to high vigor (70%). However, as the sorghum plants grow, the difference between genotypes become more apparent, especially at the generative phase. For instance, three different panicle shapes have been observed, erect (50%), semi-bent (30%), and bent (20%) with different degree of compactness (20% for loose, semi-compact, and compact panicles, and 30% for semi-loose panicles). In another part of this study, the phytochemical composition and antioxidant activities of the sorghum ecotypes have been determined. The results showed variable total phenolic contents, and total flavonoid contents ranging from 125.86 ± 1.36 to 314.91 ± 3.60 mg GAE/g dw and 114.0 ± 13.2 to 138.5 ± 10.8 (mg catechin equivalent/100 g, dw) respectively, with a differential antioxidant activities as well. These results indicate that for any crop breeding program, it is preferable to take into consideration both morphological and biochemical traits for a better selection of high yielding varieties with high added value compounds. Therefore, the implication of these results in the context of sorghum breeding activities could be a resourceful option for farmers.

Nitrogen stress as well as other stresses can negatively impact the plant development and metabolism. Generally, stress factors increase the reactive oxygen species (ROS) and methylglyoxal (MG) production, which may, in the absence of effective protective mechanisms, induce irreparable metabolic dysfunction and death. The effect of different amounts (from deficiency to excess) of nitrate, ammonium or nitrate combined to ammonium, on enzyme activities of antioxidant and methylglyoxal detoxification systems of two sorghum ecotypes (3P4 and 4P11) was studied. The N supply was performed per pot during the sowing step using potassium nitrate and/or ammonium sulfate. Six N treatments were applied using 120, 240 and 480 Kg ha-1 of ammonium or nitrate and three other treatments were applied using 120 kg ha-1 nitrate combined to 120, 240 and 480 kg ha-1 of ammonium. The specific activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), glutathione reductase (GR), glyoxalase I (Gly I) and glyoxalase II (Gly II) were investigated. Results showed that, ammonium excess and N-deficient conditions increased the contents of malondialdehyde (MDA), and induced the enzyme activities of ROS and MG detoxification systems, supporting the sorghum's ability to counteract the negative effect of N stress (deficit and excess). We have also shown that the SOD, CAT, GR and Gly I enzyme activities were higher in the 4P11 ecotype compared to the 3P4 ecotype. These results indicate that sorghum ecotypes exhibit differential tolerance to N stress and suggest that the 4P11 ecotype has higher capacity to cope with N stress.