Cereal endosperm, cell wall

The subject of the secondary protein structure as a means of defining the performance characteristics ofwheat endosperm-known as hardness-been explored over a seven year period [39, 40]. Another approach, taken by Baron et al., involves the IMS imaging of the endosperm cell walls rather than of the protein found in the endosperm itself [61]. All of these authors performed the imaging in situ, following removal of the protein and starch, in order to study the compositional and architectural heterogeneity and, in relation to this, wheat hardness. In this case, the research was focused on kernel hardness rather than on endosperm hardness, as was the case with our studies. A further study of carbohydrate polymers by the same group involved the investigation of cereal arabinoxylans in relation to their structure and physico-chemical properties. 

Preparation of Cell Walls from Cereal Endosperm... 

Suspension-cultured tissues of cereal endosperm Cells containing mainly primary cell walls Hemicelluloses (mainly acidic arabinoxylans and p-D-glucans) cellulose, some phenolics and phenolic esters, and proteoglycans... 

Seeds other than cereals Parenchymatous (e.g., cotyledons of peas) and some cells with thickened endosperm walls (e.g., guar) Same as parenchymatous tissues of dicotyledons Galactomannans and small amounts of cellulose, pectic substances, and glycoproteins... 

A range of methods have been described in the literature, and we shall consider them in the following order (1) the methods developed at the Food Research Institute-Norwich (FRIN), to isolate cell walls from a range of vegetables and fruits (runner beans, potatoes, cabbage and apples), cereals (oats, wheat and rye) and cereal products (wheat bran and rye biscuits), and lignified tissues (parchment layers of runner bean pods) (2) the special techniques, which may include wet sieving steps, used for the isolation of cell walls from potatoes, wheat endosperm, and wheat and barley aleurone layers (3) alternative methods for the isolation of cell walls from starch and protein-rich products (rice) and (4) methods used for the isolation of cell walls from suspension-cultured tissues. 

Since the cell walls from most cereal endosperm contain little or no pectic substances, extraction with a chelating agent could be omitted. Various workers have used different schemes for extraction (Mares and Stone, 1973a Anderson and Stone, 1973 Fincher, 1975 Ballance and Manners, 1978), so it is difficult to make firm recommendations. However, the following sequential treatments of the CWM (1 g) may prove useful to effect partial fractionation of the polymers (1) The loosely held polysaccharides could be solubilized by incubation with 100 ml of 10 mM NaOAc, pH 5, at 40°C for 2 h three times. If the CWM is not completely free of... 

The endosperm of members of the Gramineae and certain other species (e.g. Trigonella, Fagopyrum) is characterized by the possession of an outer aleu-rone layer. As the seed begins to mature, the peripheral cells of the endosperm which cut off cells internally begin to divide anticlinically to form small cells of rectangular appearance in section. One or more layers of such cells may be produced they become fairly thick-walled, develop protein bodies called aleurone grains and, most important, remain alive, unlike for example the other endosperm cells of cereals which are dead cells packed with starch and to a lesser extent protein. 

Cereals also contain polysaccharides other than starch. In endosperm cells their content is much less than that of starch (cf. Table 15.29). They include pentosans, cellulose, 3-glucans and glu-cofructans. These polysaccharides are primarily constituents of cell walls, and are more abundant in the outer portions than the inner portions of the kernel. Therefore, their content in flour increases as the degree of fineness increases (cf. rye as an example in Table 15.36). 

In foods heteroxylans are mainly present in cereals, found in thin endosperm cell walls, the aleurone layer and lignified bran cells. The endosperm cell walls of most cereals contain 60-70% arabinoxylans, with 20% in barley and 40% in rice. Glumes (husks) of wheat grains contain about 64% heteroxylans. Wheat grains contain on average 1.4-2.1% of heteroxylans, of which 0.8-1.5% represent water soluble pentosans. Rice grains contain 7-8% heteroxylans. 

P., and Mills, E. (2012) Spectroscopic analysis of diversity in the spatial distribution of arabinoxylan structures in endosperm cell walls of cereal species in the HEALTHGRAIN diversity collection. J. Cereal Sci, 56 (2), 134-141. 

Verbmggen MA, Beldman G, Voragen AGJ. 1995. The Selective Extraction of Glucuronoarbinoxyltms from Sorghum Endosperm Cell Walls Using Barium and Potassium Hydroxide Solutions. J. Cereal Sci. 

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