Aleurone concentrate

An ABA analog with a fluorescent group at C-4, 6, was synthesized in two steps from ABA by Asami et al. [27]. This analog exhibited the ABA activity in an inhibitory assay of a-amylase induction in aleurone protoplasts of barley, although it required a 30-fold higher concentration than ABA. Kohler et al. reported C-4 biotinylated ABA (7), which showed 1/10 -1/100 the activity of ABA [28]. 

Increasing the amounts of minerals and vitamins in the grain may not, however, be sufficient to improve the diet of consumers because they are concentrated in the pericarp, aleurone, and germ and are hence removed by decortification. It is therefore necessary to increase the concentration of vitamins and minerals in the endosperm and, in the case of minerals, their availability. 

However, the concentrations of minerals, vitamins, and phytochemicals are very high in the bran and their removal lowers the nutritional value. Some data for the concentrations of vitamins and minerals in the starchy endosperm and the aleurone components are shown in Table 14.1. Myriad different chemical compounds can be found in the whole grain of cereals, some of which may not yet have been identified. Therefore, cereal chemists have a great challenge for the future to identify them and to contribute to elucidating their role in improving health. 

Fig. 1 21]. An ABA concentration as low as 10 M is sufficient to enhance its own metabolism, and this effect can be observed within 2 h of ABA treatment [21]. The formation of the next stable metabolite, DPA, is not enhanced by pretreatments with either ABA or PA [21]. Thus, the enhanced PA formation is unlikely a scavenging mechanism to remove excessive ABA because the tissue would have to enhance the formation of DPA in order to eliminate the biological activities. The self-induction of ABA metabolism can be prevented by transcription and translation inhibitors, suggesting that ABA induces the monooxygenase (or a cofactor for this enzyme) responsible for PA formation. The regulation of ABA metabolism in barley aleurone layers is similar to the induction of nitrate reductase by its substrate, nitrate. In this latter case, treatment of a plant tissue with nitrate enhances its ability to metabolize nitrate. 

Phytin content of whole seeds and protein bodies varies with species and cultivar. Examples of the chemical composition of the aleurone grains of rice and protein bodies (and isolated globoids) of cotton seed are shown in Table 2.7. Note, in particular, the higher phosphorus but lower protein content of the cereal aleurone grain in comparison with the dicot protein body. The concentration of the associated macronutrient elements can also be seen to differ. Qualitative as well as quantitative differences occur between the macronutrient compositions of different seeds, e.g. in C. maxima the globoid is rich in phosphate, potassium... 

Studies on the early responses of aleurone layers to GA have shown that a-amy-lase is not the first enzyme to be secreted. Within 5 h of the addition of GA to isolated aleurone layers of barley (cv. Betzes) there is increased secretion into the surrounding medium of several hydrolytic enzymes, including an ATP-ase, phytase, j -glucosidase and phosphomonoesterase, as well as some soluble carbohydrate [96] (probably sucrose). Similar observations were made using GA-treated half-grains of both barley and wheat (the distal embryoless half), although in barley additional enzymes, e.g. an esterase, phosphodiesterase and a-galactosidase were also found to be secreted early [96]. From the limited information available to date it appears that some enzymes which are secreted early after GA addition (e.g. phosphomonoesterase and phosphodiesterase) do so in response to lower concentrations of GA than do the later ones (e.g. a-amylase) [97]. Furthermore, a-amylase and proteinase, which are secreted simultaneously, have identical GA dose-response curves (Fig. 7.5A and B). There are exceptions, however, and further work on more enzymes is required to determine if the sequence of enzyme production by aleurone tissue is related to GA concentration in the cells. 

Fig. 7.7. (A) Dose-response curve of the production of ribonuclease by aleurone layers at different concentrations of GA. Enzyme activity was measured in the medium and an extract of the tissue after 48 h incubation of the isolated aleurone layers. (B) Time course of ribonuclease production by 10 aleurone layers incubated with 5nM GA. Ar-rowed is the time of a-amylase release (see Figure 7.1 A). After Chrispeels and Varner, 1967 [22]...

An important observation by Paleg is that the steryl ester and steryl glycoside content of wheat aleurone tissue decreases markedly and rapidly after imbibition of water by the dry seed. The fall in steryl ester and glycoside content is accompanied by a complementary increase in the free sterol content. These changes in steryl conjugate and free sterol concentrations in the aleurone cells are compatable with the... 

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