Vitamin C (l-ascorbic acid) is an excellent free radical scavenger, not only for its capability to donate reducing equivalents but also for the relative stability of the derived monodehydroascorbate radical. However, vitamin C is not only an antioxidant, since it is also a cofactor for numerous enzymes involved in plant and human metabolism. In humans, vitamin C takes part in various physiological processes, such as iron absorption, collagen synthesis, immune stimulation, and epigenetic regulation. Due to the functional loss of the gene coding for l-gulonolactone oxidase, humans cannot synthesize vitamin C; thus, they principally utilize plant-based foods for their needs. For this reason, increasing the vitamin C content of crops could have helpful effects on human health. To achieve this objective, exhaustive knowledge of the metabolism and functions of vitamin C in plants is needed. In this review, the multiple roles of vitamin C in plant physiology as well as the regulation of its content, through biosynthetic or recycling pathways, are analyzed. Finally, attention is paid to the strategies that have been used to increase the content of vitamin C in crops, emphasizing not only the improvement of nutritional value of the crops but also the acquisition of plant stress resistance.

Soil nitrogen abundance, as well as nitrogen use efficiency (NUE), significantly affect the crop yield and grain protein content (GPC). Depending on the genotype, a negative correlation between the yield and GPC can occur. The aim of the study was to assess the agronomic performance, and to explore physiological pathways for the efficient use of N fertilizer for two durum wheat cultivars, “Aureo” and “Vespucci”. After fertilization, the nitrogen content and values of some of the agronomic parameters and yield-related traits increased in both cultivars; nevertheless, a simultaneous rise in both the yield and GPC occurred only in Aureo. The biochemical parameters, analyzed at tillering, confirm the genotypic specificity of nitrogen use. In Vespucci’s roots, the nitrogen supply did not affect the nitrate reductase (NR), but greatly increased the amino acids and proteins, suggesting that ammonium is preferentially assimilated. In Aureo, nitrate is in part assimilated by the roots, as suggested by the ammonium increase and NR enhancement. In the leaves of both cultivars, organic nitrogen significantly increased after fertilization; however, the rise in amino acids, as well as in NR activity, was higher in Aureo than in Vespucci. These results indicate that the different nitrogen use, and in particular the diverse NR behavior, at tillering, are in part responsible of the cultivar differences in grain yield and GPC.