Changes in accumulation of seed nitrogen compounds in maize under conditions of sulphur deficiency

Abstract

Maize (Zea mays L., hybrid INRA 260) was grown in the greenhouse with mineral nutrition of different sulphate concentrations. Mature seeds from these plants were compared for their free amino acid and protein N forms. For the most S‐deficient sample, the Asx (asparagine + aspartic acid) content increased by 30% as compared with control, while methionine and cysteine decreased (by 25 and 30%, respectively), as well as glycine, lysine, histidine, arginine and tryptophan. In seeds lowest in S the non‐protein N to total N ratio was 77% higher than in the control. Free asparagine dominated in starved seeds (50 mol % of total free amino acids) and was ten‐fold more concentrated than in the control, where proline was the predominant free amino acid. Thus the Asx of non‐protein N reached 28% of the total mol Asx of the whole starved seed. Altered S nutrition had virtually no effect on the amino acid composition of the main protein fractions, but it significantly changed their ratios. Zeins, which are poor in S‐containing amino acids, showed 25% higher level than in seeds supplied with normal S. As a counterbalance, two glutelin subfractions rich in S‐containing amino acids, decreased by 36–71% under limiting S nutrition. It is concluded that the plant reacts against S deficiency by modifying its N metabolism. Significant accumulation occurred of free asparagine, which is the main form of N transportation. The biosynthesis of seed storage protein occurred through the accumulation of the highest possible protein quantity allowed by the available S‐containing amino acids, i.e. proteins low in S‐containing amino acids were preferentially synthesized.

Asparagine in plants

“…When plants are grown under sulphur‐deficient conditions, there is a reduction in the synthesis of the amino acids cysteine and methionine and the antioxidant glutathione (Nikiforova et al , 2006). In maize seeds, such a deficiency in sulphur has been shown to give rise to an alteration in the proportion of types of protein formed and an increase in soluble asparagine to 50% of the total pool (Baudet et al , 1986). In maize suspension culture cells, the increase in asparagine accumulation following sulphur starvation was shown to be as a result of de novo synthesis and not protein hydrolysis (Amancio et al , 1997).…”

Transport‐related amino acid metabolism in germinating barley grains

“…A 10-fold accumulation of free asparagine also occurred in developing maize kernels when protein synthesis was limited by deficiency of sulphur, while no or much smaller increases were observed in the contents of other amino acids (Baudet et al, 1986). Taken together, the data suggest that in cereals glutamine acts as a transport form of nitrogen whereas asparagine is used for short-term storage of N. In seedlings growing through the soil (in the dark), this seems a useful adaptation whieh makes possible the rapid growth beginning after the onset of photosynthesis.…”

Genetic and agronomic approaches to decreasing acrylamide precursors in crop plants

“…When plants are grown with a plentiful supply of nitrogen, deficiencies in potassium, sulphur, phosphorus and magnesium, but not molybdenum, stimulate accumulation of asparagine (Possingham, 1956, Stewart and Larher, 1980, Rabe and Lovatt, 1986, Rufty et al, 1990, Almeida et al, 2000, Nikiforova et al, 2006. However sulphur deficiency leads to the greatest asparagine accumulation and in conditions of severe sulphur deprivation asparagine can accumulate to up to 50 % of the total free amino acid pool (Shewry et al, 1983, Baudet et al, 1986. This is discussed in more detail later in the review.…”