View/Open - ResearchSpace - University of KwaZulu-Natal
View/Open - ResearchSpace - University of KwaZulu-Natal
View/Open - ResearchSpace - University of KwaZulu-Natal
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Literature review<br />
The embryo is the diploid result <strong>of</strong> fertilization and is a minute autotrophic plant<br />
(EDMOND et al., 1964). The embryo principally consists <strong>of</strong> an embryonic axis and at<br />
least one cotyledon (BEWLEY & BLACK, 1994). The axis further consists <strong>of</strong> the<br />
embryonic root (radicle), the hypocotyl with attached cotyledons and the shoot apex<br />
with the first true leaves (plumules) attached (BEWLEY & BLACK, 1994).<br />
The nourishing tissue is generally either the endosperm or cotyledons (EDMOND et<br />
al., 1964). In the case <strong>of</strong> endospermic seeds, the endosperm, which is present in the<br />
mature seed, serves as a food storage organ (HARTMANN & KESTER, 1965). Here<br />
the testa and endosperm are the two layers covering the embryo (BEWLEY &<br />
BLACK, 1994). In non-endospermic seeds the cotyledons serve as the sole food<br />
storage organ (BEWLEY & BLACK, 1994). During development, the cotyledons<br />
absorb the food reserves from the endosperm. Here the embryo is enclosed by the<br />
testa and the endosperm is all but completely degraded in the mature seed<br />
(BEWLEY & BLACK, 1994).<br />
In some cases the testa exists in a rudimentary form only and the prominent and<br />
outermost structure is the pericarp or fruit coat derived from the ovary wall<br />
(HARTMANN & KESTER, 1965). In such cases the embryo is also encased in a fruit<br />
(BEWLEY & BLACK, 1994). The seed coverings provide mechanical protection to the<br />
embryo and make transportation and storage <strong>of</strong> seeds possible (HARTMANN &<br />
KESTER, 1965).<br />
Hairs or wings, which aid in seed dispersal, sometimes develop as a modification <strong>of</strong><br />
the enclosing fruit coat (BEWLEY & BLACK, 1994). These are attached via the hilum<br />
(BEWLEY & BLACK, 1994). The hilum is a funicular scar on the seed or fruit coat<br />
that marks the point at which the seed was attached via the funiculus to the ovary<br />
tissue (LAWRENCE, 2000). In many cases a small hole, called the micropyle, can be<br />
seen at the end opposite to the end with the hilum (BEWLEY & BLACK, 1994).<br />
Seeds store various substances that are important for germination and early seedling<br />
growth. These primarily include carbohydrates, fats and oils, and proteins (MAYER,<br />
1977; BEWLEY & BLACK, 1994). Other important substances that are only stored in<br />
small amounts include alkaloids, lectins, proteinase inhibitors, phytin, and raffinose<br />
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