Fructan contents and dry matter deposition in different tissues of the wheat grain during development

Abstract

The role of fructan metabolism in the assimilate relations of the grain of wheat (Triticum aestivum L.) was investigated by determination of the dry matter and fructan content of grain components at short intervals during grain filling. During the initial phase of rapid expansion, most of the assimilates entering the grain were partitioned to the outer pericarp. A large fraction of these assimilates were used for the synthesis of fructan. Dry matter deposition and fructan synthesis in the outer pericarp ceased at about 5d after anthesis. At the same time, the endosperm and the inner pericarp and testa started to accumulate dry matter at a fast rate. This was also associated with significant fructan synthesis in the latter tissues. The outer pericarp lost about 45% of its former maximum dry weight between 9 and 19 d after anthesis. This loss was due almost entirely to the near complete disappearance of water‐soluble carbohydrates, most of which was fructan. The inner pericarp and testa accumulated dry matter until about mid‐grain filling. The fructan contents of the inner pericarp and testa and the endosperm decreased slowly towards the end of grain filling. Most of the fructans in the inner pericarp and testa and the endosperm had a low molecular weight, whereas higher molecular weight fructans predominated in the outer pericarp. The embryo did not contain fructan. The presence of low molecular weight fructans in the endosperm cavity at mid‐grain filling was confirmed. It is suggested that fructan synthesis is closely linked to growth‐related water deposition in the different tissues of the wheat grain and serves to sequester the surplus of imported sucrose.

Spatio-Temporal Dynamics of Fructan Metabolism in Developing Barley Grains

“…Grain filling initiation was accompanied with increasing DP 3 and 4 oligofructan levels (Figure 3), known to be present in the cereal grain (Henry and Saini, 1989;Verspreet et al, 2013b). Larger amounts of fructosyl oligosaccharides are also present in the wheat endosperm cavity at 20 to 27 DAP (Ugalde and Jenner, 1990;Schnyder et al, 1993). Here, the visualization by MSI showed that these molecules were associated with the NP and ETCs, rather than being within the cavity itself (Figure 2).…”

“…Similarly, watersoluble carbohydrates accumulate in the pericarp of the very young wheat grain (Housley and Pollock, 1993;Schnyder et al, (D) Enzymatic pathways involved in oligofructan metabolism. Sucrose is the precursor of fructan biosynthesis; it is used by 1-SST or 6-SFT to produce either inulin-or levan-type fructans, which differ in their linkages with fructose moieties (b2-1 or b2-6).…”

“…Studies on the metabolic compartmentation within developing barley grains so far showed local variation in endospermal sucrose and alanine concentration Rolletschek et al, 2011), which might be correlated to uneven levels of hypoxia within the grain (Rolletschek et al, 2004). Although it has long been known that fructosyl oligosaccharides are enriched in the endosperm cavity of the wheat (Triticum aestivum) grain during late storage (20 to 27 DAP) (Ugalde and Jenner, 1990;Schnyder et al, 1993), their role in grain development remains unclear. Fructans are a recognized constituent of cereal grains of different species (Henry and Saini, 1989); they also feature in vegetative tissues and have been implicated in carbohydrate partitioning, short or longer term storage (Nelson and Spollen, 1987;Schnyder et al, 1993), and stress protection (Valluru and Van den Ende, 2008;Livingston et al, 2009).…”

“…Although it has long been known that fructosyl oligosaccharides are enriched in the endosperm cavity of the wheat (Triticum aestivum) grain during late storage (20 to 27 DAP) (Ugalde and Jenner, 1990;Schnyder et al, 1993), their role in grain development remains unclear. Fructans are a recognized constituent of cereal grains of different species (Henry and Saini, 1989); they also feature in vegetative tissues and have been implicated in carbohydrate partitioning, short or longer term storage (Nelson and Spollen, 1987;Schnyder et al, 1993), and stress protection (Valluru and Van den Ende, 2008;Livingston et al, 2009). In the grain, the presence of fructans has been associated with both sucrose phloem unloading (Pollock and Cairns, 1999;De Gara et al, 2003) and osmoregulation during cell expansion and growth (Schnyder et al, 1993).…”

“…Fructans are a recognized constituent of cereal grains of different species (Henry and Saini, 1989); they also feature in vegetative tissues and have been implicated in carbohydrate partitioning, short or longer term storage (Nelson and Spollen, 1987;Schnyder et al, 1993), and stress protection (Valluru and Van den Ende, 2008;Livingston et al, 2009). In the grain, the presence of fructans has been associated with both sucrose phloem unloading (Pollock and Cairns, 1999;De Gara et al, 2003) and osmoregulation during cell expansion and growth (Schnyder et al, 1993). Verspreet et al (2013b) propose a role for wheat grain fructans in reactive oxygen species (ROS) detoxification related to cell division processes during prestorage.…”