Caryopsis aleurone layer

Figure 1. Scanning electron micrograph of the cell wall preparations obtained from the different parts of rice grain (7). Caryopsis coat (upper left), aleuron layer (upper right), germ (lower left) and starchy endosperm (lower right). Bars in the picture indicate 5 /zm.

While the hemicelluloses obtained from the germ, aleuron, and caryopsis coat cell walls all showed a similar monosaccharide composition, this was not the case for the endosperm tissue. Thus, a major difference in the structure of hemicellulosic polysaccharides exists between the preparations obtained from the endosperm cell walls and those from the cell walls of the other parts of the grain, i.e., rice bran. (Rice bran consists of the caryopsis coat, aleuron layer and germ.) Comparison of the detailed structural features of the hemicellulosic polysaccharides of endosperm and bran cell walls will be discussed in the following sections. 

The caryopses of grasses and cereals are anatomically complex. The starch endosperm of the caryopsis is surrounded by the aleurone layer and pericarp, both of which can be partly or completely removed, along with the embryo, by the abrasive process known as pearling, which removes the bran. The flour obtained by milling a pearled grain consists of protein, starches, and a low proportion of endospermic hemicellulose and non-endospermic hemicellulose from the bran. 

FIGURE 4.3 Microphotograph detailing the microstructure of the pericarp and aleurone layer of the sorghum caryopsis. E = epicarp M = mesocarp S = starch granules CC = epicarp cross cells T = epicarp tube cells SC = seed coat or testa A = aleurone cells P = peripheral endosperm (courtesy of C. McDonough and L. W. Rooney, Texas A M University). 

FIGURE 4.3 Microphotograph detailing the microstructure of the pericarp and aleurone layer of the sorghum caryopsis.117... 

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