Seed Germination

the transition of seeds from a dormant state to intensive vital activity, as a result of which the embryo begins growing and a sprout is formed from which a young plant develops; the initial stage of plant ontogeny.

Seed germination occurs only when there is adequate moisture and oxygen; proper temperature and, in some cases, certain light conditions are other requirements. When seeds germinate, metabolism in the embryo and endosperm increases. As water enters the seeds they swell, their enzymes become activated, and the conversion of such storage materials within the seeds as starch, fats, and proteins is intensified, with decomposition primarily into sugars, fatty acids, and amino acids. This provides the seeds with energy and the plastic substances necessary for the synthesis of matter used to form the sprout’s new tissues.

When the seed has stopped swelling, the embryo begins growing. As a rule, the radicle grows first and ruptures the seed coat; this is known as sprouting. In some plants, the hypocotyl grows next. As a result, the cotyledons and terminal bud emerge to the soil surface. In other plants, the epicotyl grows next: the cotyledons remain in the soil, and only the terminal bud emerges to the surface. The amount of water required for germination depends on the chemical composition and physiological state of the seed. If there is insufficient oxygen, as when seeds are immersed in water over a period of time or when there is formation of a soil crust, ethyl alcohol, lactic acid, ammonia, and other substances harmful to the embryo accumulate in the seeds.

Temperature affects seed germination because of penetration of moisture into the seed, acceleration of metabolism, and a change within the seed in the relationship of various growth regulators. For example, when freshly gathered cotton or peanut seeds are heated, the content of growth inhibitors in them decreases and germination accelerates. On the other hand, in order to accelerate germination of many other plants a low positive temperature is required: this causes an increase in the content of gibberellins and other growth stimulators.

In addition to moisture, oxygen, and proper temperature, some plants require light of a certain spectrum for seed germination. Thus, red light stimulates germination in lettuce, pine, and dock, whereas infrared light inhibits it. Even in the same plant, one spike may require different environmental conditions for seed germination. The seeds of some plants do not germinate even under favorable conditions. In such cases, either the seeds have not emerged from the quiescent state, or they have hard coats that do not allow passage of oxygen and water to the embryo. When this is the case, as with almonds, walnuts, and grapes, the seed coats are scarified.

Seed germination ends when the sprout is capable of autotrophic nourishment: this coincides with the appearance of seedlings. For this reason, the establishment of optimal conditions for increased germination is a prerequisite for obtaining high yields.