Abstract
As a primary food crop, maize is widely grown around the world. However, the deficiency of essential amino acids, such as lysine, tryptophan, and methionine, results in poor nutritional quality of maize. In addition, the protein concentration of maize declines with the increase in yield, which further reduces the nutritional quality. Here, the photosynthesis of leaves, grain amino acid composition, and stoichiometry of N and S are explored. The results show that N and S maintained the redox balance by increasing the content of glutathione in maize leaves, thereby enhancing the photosynthetic rate and maize yield. Simultaneously, the synergy of N and S increased the grain protein concentration and promoted amino acid balance by increasing the cysteine concentration in maize grains. The maize yield, grain protein concentration, and concentration of essential amino acids, such as lysine, tryptophan, and methionine, could be simultaneously increased in the N:S ratio range of 11.0 to 12.0. Overall, the synergy of N and S simultaneously improved the maize yield and nutritional quality by regulating the redox balance of maize leaves and the amino acids balance of grains, which provides a new theoretical basis and practical method for sustainable production of maize.
Highlights
Contemporary grain production faces great challenges, including that more than 1 in 10 people still do not have access to sufficient energy and protein in their diets even with recent productivity gains (Food and Agriculture Organization of the United Nations, 2018)
For each N level, the Rubisco activity and GSH content increased with the increase of S application rates and reached a maximum (267.2 nmol min−1 g−1, 16.9 nmol mg−1) at the N3S3 and N2S3 treatments, which was significantly higher than the N0S0 treatment (113.2 nmol min−1 g−1, 6.2 nmol mg−1)
The results showed that protein concentration of grains correlated significantly with cysteine concentration in maize (Figure 8A), which indicated that the formation and stability of protein were enhanced with cysteine concentration
Summary
Contemporary grain production faces great challenges, including that more than 1 in 10 people still do not have access to sufficient energy and protein in their diets even with recent productivity gains (Food and Agriculture Organization of the United Nations, 2018). Subsequent studies show that, with the N application rates increased, the zeins lacking EAA significantly increased, and the concentration of EAA, such as lysine and threonine, continuously decreased, which exacerbated the imbalance of amino acids in grains (Tsai et al, 1992; Lošák et al, 2010). The concentration of methionine and cysteine in S-deficient maize grains decreased by 25% and 30%, respectively, and the concentration of asparagine and aspartic acid increased by 30%, which seriously reduced the nutritional quality of maize (Baudet et al, 1986). The regulation mechanism of N and S was proposed to synergistically enhance maize yield and nutritional quality by maintaining the redox balance in maize leaves and promoting amino acid balance in maize grains
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