Cereals embryo reserves

In the germination of cereal seeds, it was long known by brewers that if the embryo was excised (or dead) the endosperm would not be hydrolyzed and sugars would not be released. In 1960, Paleg showed that amylolytic activity in the embryo-less half could be fully restored in the presence of gibberellin. In other words, the substance that passed from the embryo to the endosperm (or rather, to the living cells of the aleurone layer that encloses the dead endosperm) induces there the synthesis of a-amylase which is responsible for hydrolysis of the stored starch reserves held in the endosperm. The extent to which the a-amylase was induced became another bioassay for gibberellin. 

In angiosperms, endosperm growth starts before the zygote begins to divide. The endosperm may be absent in mature seeds, since it has been utilized by the growing embryo and in this case reserves accumulate in the cotyledons (many leguminous seeds) on the other hand, the endosperm may persist in other species and constitute a reserve, as in cereal seeds or castor bean seeds. 

A large section of this Chapter is devoted to the production and storage of reserves in the seed, for it is upon such reserves that the embryo will eventually depend, not so much for germination, but for its successful subsequent growth and development into a seedling. Work on the physiology and biochemistry of seed maturation has been limited almost exclusively to a few commercially important annuals. For convenience we shall consider nutrient assimilation in the cereals, which have a persistent endosperm, then those dicots in which... 

It would obviously be of great interest to know whether two distinct patterns of reserve mobilization really do occur within cereals. It is still possible that there is fundamentally only one (GA-dependent) and that the endosperms of maize and sorghum contain sufficient endogenous GA (produced there during development) to stimulate maximum hydrolase production without a requirement for a further supply from the embryo, or without any additional effect of exogenously added GA. The effect of added GA on maize endosperm (aleurone layer) probably varies in different hybrid or inbred lines because some already have a high endogenous GA level while others, e.g. dwarf maize, are naturally deficient in GA. The latter show a three- to five-fold increase in hydrolase production in response to added GA [64] (see Chap. 7). 

We saw in Chapter 6 how the reserves in the endosperm of cereals are mobilized largely as a result of the activity of enzymes secreted by the aleurone layer. We also referred to the stimulation of aleurone layer activity by gibberellin coming from the embryo. Herein lies the basis of the control exerted by the embryo over food mobilization, which we will now examine more closely. 

Cereal grains are the seeds of the plant and they house the embryo and the necessary food reserves required for germination. Forming the dietary staples in many countries, the major grains in the human diet are wheat, rice, and corn (maize). Consumption of oats, millet, barley, sorghum, and rye are more limited. 

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