Germination of Seeds

A seed consists essentially of a seed coat, stored food and a young plant, the embryo. The seed coat may be made of inner tegmen and outer testa. On the seed coat a scar (hilum) is present which shows the place of attachment of a seed in the fruit is present. At one end of the hilum is the micropyle. Through micropyle the seed absorbs water during the process of germination. The embryo consists of epicotyl,one or two seed leaves called cotyledons, and a hypocotyle. The portion of the embryo above the point of attachment of cotyledons to embryo axis, and below the plumule is called epicotyl.

The plumule forms shoot. the portion of the embryo below the point of attachment of cotyledons to embryo axis but above the radicle, is called hypocotyls. The radicle forms root. The seed also contain the food, derived from the endosperm tissue. The food may remain as such or may be digested and stored in the cotyledons. Thus the cotyledons become thick due to the presence of stored food. This food is supplied to the developing plant during the process of germination of seeds. In the grain of maize, the cotyledon is modified into an organ called scutellum a term that comes from the Latin word meaning “Shield”.

The food stored in scutellum is used first during germination of seed. Later on scutellum absorbs the food of endosperm and supply it to the developing embryo.

During germination (growth and development) of a seed the water is absorbed through micropyle, and the formerly dormant embryo resumes growth and emerges from the seed. The root is normally the first structure emerging the seed, growing rapidly and absorbing water and minerals from the soil. Much of the water is transported to the cells in embryo.

Through micropyle, the seed absorbs water, which swells it causing the seed coat to burst. This helps the root to emerge out of seed. Water absorbed by the germination seed helps to activate the enzymes to digest the food of seed, which is made available to the growing embryo. It also helps to elongate hypocotyls and epicotyl, to grow out. (ii) Air Because oxidative metabolism usually takes over soon after a plant embryo starts to grow, most seeds require oxygen for germination. So air is very important for germination as it contains about 21% of oxygen, which is used during respiration. iii)Suitable temperature Germination of seeds occur over a wide temperatue range between 5-30 C. the optimum temperature for the germination of seeds of most plants ranges between 25-30 C. optimum or suitable temperature is necessary for the enzymes to function. During early germination of seeds, the vital mobilization of food reserves stored in the embryo cotyledons or the endosperm is mediated by hormones, which in some cases are gibberellins.