Cotyledons reserves

Establishment of Cotyledon Reserves in Dicots 75 Table 3.2. Composition of castor bean seed at various stages of development... 

Cucurbit seeds are exalbuminous or lacking endosperm in the mature state. In such seeds the embryo is large in relation to the seed as a whole. It fills the seed almost completely and its body parts, particularly the cotyledons, store the food reserves for germination. Since the predominant tissue of the seed is cotyledonous, and since cotyledons are leaves, anatomy and histology of typical leaf tissue suffice to describe the preponderant part of the seed. Epidermal cells cover the cotyledonary surface followed by palisade and abundant parenchyma cells that contain the food reserves. Vascular tissues are also present. 

To properly evaluate data relating to reserve starch development and composition, cellular development of tissues in which this starch is formed must be appreciated. Enlarging potato tubers,38 cotyledons of developing pea seeds39 and endosperms... 

It has been known for some time that the albuminous seeds of the family Leguminosae contain, in the endosperm, galactomannan as the reserve polysaccharide. The exalbuminous seeds, on the other hand, have the main reserve in the cotyledon in the form of starch, oil, and proteins.198,199 The seed galactomannan-reserves are generally mobilized during the process of germination.43,57,81,82,199-205 Detailed study... 

The amount of canavanine (37) declines rapidly upon germination of the seed one function of canavanine is to serve as a nitrogen storage reserve in the plant. Radioactively labeled canavanine and related metabolites were converted into glutamic acid, glutamine, and alanine in cotyledons of Canavalia ensiformis (Rosenthal et al., 1988). 

The seeds of many plants contain fat as the major carbon reserve in some, such as those of castor bean, this is stored in the endosperm tissue surrounding the embryo, while in those of cucurbits and other plants it is stored in the cotyledons. Electron micrographs of the storage tissue show that the cells are almost completely occupied by spherosomes (membrane-bound vesicles of fat) and by protein bodies (e.g.. Vigil, 1970). 

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. 

It must be realized, however, that reserves are frequently present in some measure throughout the whole seed. In lettuce, for example, though most of the protein and oil stores are located in the cotyledons, protein and oil bodies nevertheless do occur in the radicle/hypocotyl region. Additionally the endo-... 

Fig. 2.6A-E. Histology of food reserves 1. (A) Cotyledon cells of mung bean (Phaseolus aureus). From Harris and Chrispeels, 1975 [33]. (B) and (C) Electron micrographs of meso-phyll cell and epidermal cells (B) and protein body (C) of squash (Cucurbita maxima) cotyledons. From Lott et al., 1971 [46]. (D) and (E) Electron micrographs of a barley Hordeum vulgare) aleurone cell with aleurone grains (D) and aleurone grain (E). From Jacobsen et al., 1971 [40]. C crystalloid, G globoid, GC globoid cavity, PCB protein carbohydrate body, PB,pb protein body, PM protein matrix. Land S oil bodies, A and n nucleus, st starch grains...

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