Skip to main content
Select Source:

germination

germination, in a seed, process by which the plant embryo within the seed resumes growth after a period of dormancy and the seedling emerges. The length of dormancy varies; the seed of some plants (e.g., most grasses and many tropical plants) can sprout almost immediately, but many seeds require a resting stage before they are able to germinate. The viability of seeds (their capacity to sprout) ranges from a few weeks (orchids) to up to 1,200 years (sacred lotus) and 2,000 years (date palm). The percentage of viable seed decreases with age. Dormancy serves to enable the seed to survive poor growing conditions; a certain amount of embryonic development may also take place. Dormancy can be prolonged by extremely tough seed coats that exclude the water necessary for germination. Internally, growth is regulated by hormones called auxins. When the temperature is suitable and there is an adequate supply of moisture, oxygen, and light—although some seeds require darkness and others are unaffected by either—the seed absorbs water and swells, rupturing the seed coat. The growing tip (radicle) of the rudimentary root (hypocotyl) emerges first and then the growing tip (plumule) of the rudimentary shoot (epicotyl). Food stored in the endosperm or in the cotyledons provides energy for the early stages of this process, until the seedling is able to manufacture its own food via photosynthesis.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"germination." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. 14 Dec. 2017 <http://www.encyclopedia.com>.

"germination." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (December 14, 2017). http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/germination

"germination." The Columbia Encyclopedia, 6th ed.. . Retrieved December 14, 2017 from Encyclopedia.com: http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/germination

Germination

Germination

Seeds are usually shed from their parent plant in a mature dry state. The dry seed contains an embryo that is the next generation of the plant in miniature. Before the seed can grow, however, it must first emerge from the seed and establish itself as an independent, photosynthetic seedling. Germination, by definition, starts when the seed takes up water, a process known as imbibition, and is completed when the embryonic root, the radicle, penetrates the outer structures of the seed (usually the seed coat and, in some species, the surrounding storage tissues of the endosperm ).

In the mature dry state, the seed is metabolically inactive (quiescent) and can withstand environmental extremes of temperature and drought. When water enters the seed during imbibition there is a leakage of solutes (ions, sugars, and amino acids) because cell membranes are temporarily unstable during hydration. Cellular metabolism recommences within minutes after imbibition begins, using cell components and enzymes that were present in the dry seed. Respiration to provide energy and protein synthesis to produce new enzymes that support metabolism are important early events in germination.

Following imbibition, there is a period when no further water is taken up (plateau phase) and during which metabolism proceeds to ready the seed to complete germination. Restitution of cellular damage resulting from drying and imbibition is completed (e.g., DNA and mitochondria are repaired), and new enzymes and other proteins are synthesized. Elongation of the cells of the radicle is responsible for its emergence from the seed. Their cell walls become more stretchable and the internal water pressure (turgor) of the cells causes them to expand. Cell division and deoxyribonucleic acid (DNA) synthesis occur after radicle emergence, and later the mobilization of food reserves occurs within the storage organs of the seed to provide nutrients for post-germinative growth.

In some seeds the embryo is surrounded by a storage tissue that is sufficiently rigid to prevent extension of the radicle and completion of germination. This tissue frequently has thickened hemicellulose-containing cell walls, and a reduction in their resistance is necessary to permit radicle penetration. This might be achieved by cell-wall hydrolases or cell-separating enzymes, perhaps induced in the storage tissue in response to hormones released from the embryo late during germination.

Seeds of many noncultivated species, such as weeds, are often dormant when mature. When imbibed, these seeds exhibit the same intense metabolic activity as non-dormant seeds but do not complete germination. Germination does not occur unless the seeds receive an external stimulus (e.g., low or fluctuating temperatures, or light) while in the imbibed state. The plant hormone abscisic acid plays some role in inducing dormancy during seed development, and its application to many seeds can prevent radicle emergence. Conversely, the plant hormone gibberellic acid, when applied in low concentrations to dormant seeds, will promote the completion of germination. How abscisic acid and gibberellic acid control germination is not known.

see also Germination and Growth; Hormones; Seeds.

J. Derek Bewley

Bibliography

Bewley, J. D. "Seed Germination and Dormancy." The Plant Cell 9 (1997): 1055-66.

, and M. Black. Seeds: Physiology of Development and Germination, 2nd ed. New York: Plenum Press, 1994.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Germination." Plant Sciences. . Encyclopedia.com. 14 Dec. 2017 <http://www.encyclopedia.com>.

"Germination." Plant Sciences. . Encyclopedia.com. (December 14, 2017). http://www.encyclopedia.com/science/news-wires-white-papers-and-books/germination

"Germination." Plant Sciences. . Retrieved December 14, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/news-wires-white-papers-and-books/germination

germination

germination The beginning of growth of a seed, spore, or other structure (e.g. pollen), usually following a period of dormancy, and generally in response to the return of favourable external conditions, most notably warmth, moisture, and oxygen. The internal biochemical status of the seed or spore must also be appropriate. In seeds germination may be epigeal (i.e. with cotyledons emerging above the ground) or hypogeal (i.e. with the cotyledons staying below ground).

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"germination." A Dictionary of Ecology. . Encyclopedia.com. 14 Dec. 2017 <http://www.encyclopedia.com>.

"germination." A Dictionary of Ecology. . Encyclopedia.com. (December 14, 2017). http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/germination

"germination." A Dictionary of Ecology. . Retrieved December 14, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/germination

germination

germination The beginning of growth of a seed, spore, or other structure (e.g. pollen), usually following a period of dormancy, and generally in response to the return of favourable external conditions, most notably warmth, moisture, and oxygen. The internal biochemical status of the seed or spore must also be appropriate. In seeds, germination may be epigeal, with cotyledons emerging above the ground, or hypogeal, with the cotyledons staying below ground.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"germination." A Dictionary of Plant Sciences. . Encyclopedia.com. 14 Dec. 2017 <http://www.encyclopedia.com>.

"germination." A Dictionary of Plant Sciences. . Encyclopedia.com. (December 14, 2017). http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/germination-0

"germination." A Dictionary of Plant Sciences. . Retrieved December 14, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/germination-0

germination

germination
1. The initial stages in the growth of a seed to form a seedling. The embryonic shoot (plumule) and embryonic root (radicle) emerge and grow upwards and downwards respectively. Food reserves for germination come from endosperm tissue within the seed and/or from the seed leaves (cotyledons). See also epigeal; hypogeal.

2. The first signs of growth of spores and pollen grains.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"germination." A Dictionary of Biology. . Encyclopedia.com. 14 Dec. 2017 <http://www.encyclopedia.com>.

"germination." A Dictionary of Biology. . Encyclopedia.com. (December 14, 2017). http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/germination-1

"germination." A Dictionary of Biology. . Retrieved December 14, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/germination-1

germination

germination Growth of the embryo in the seed of a new plant. To germinate, a seed or spore needs favourable conditions of temperature, light, moisture and oxygen.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"germination." World Encyclopedia. . Encyclopedia.com. 14 Dec. 2017 <http://www.encyclopedia.com>.

"germination." World Encyclopedia. . Encyclopedia.com. (December 14, 2017). http://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/germination

"germination." World Encyclopedia. . Retrieved December 14, 2017 from Encyclopedia.com: http://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/germination