seed dormancy

Examples of seed dormancy in the following topics:

• Fruit and Seed Dispersal

  • The fruit has a single purpose: seed dispersal.
  • Modifications in seed structure, composition, and size aid in dispersal.
  • Humans also play a major role in dispersing seeds when they carry fruits to new places, throwing away the inedible part that contains the seeds.
  • Seed dormancy allows plants to disperse their progeny through time: something animals cannot do.
  • Summarize the ways in which fruits and seeds may be dispersed

• Development of the Seed

  • Monocot and dicot seeds develop in differing ways, but both contain seeds with a seed coat, cotyledons, endosperm, and a single embryo.
  • The seed, along with the ovule, is protected by a seed coat that is formed from the integuments of the ovule sac.
  • In monocot seeds, the testa and tegmen of the seed coat are fused.
  • However, many mature seeds enter a period of dormancy marked by inactivity or extremely-low metabolic activity.
  • Dormancy helps keep seeds viable during unfavorable conditions.

• Abscisic Acid, Ethylene, and Nontraditional Hormones

  • ABA inhibits stem elongation and induces dormancy in lateral buds.
  • ABA induces dormancy in seeds by blocking germination and promoting the synthesis of storage proteins.
  • Plants adapted to temperate climates require a long period of cold temperature before seeds germinate.
  • As the hormone gradually breaks down over winter, the seed is released from dormancy and germinates when conditions are favorable in spring.
  • Apical dominance, seed germination, gravitropism, and resistance to freezing are all positively influenced by hormones.

• The Evolution of Seed Plants and Adaptations for Land

  • The evolution of seeds allowed plants to reproduce independently of water; pollen allows them to disperse their gametes great distances.
  • Seed plants, such as palms, have broken free from the need to rely on water for their reproductive needs.
  • Storage tissue to sustain growth and a protective coat give seeds their superior evolutionary advantage.
  • Furthermore, seeds remain in a state of dormancy induced by desiccation and the hormone abscisic acid until conditions for growth become favorable.
  • Seed plants dominate the landscape and play an integral role in human societies.

• Subtropical Deserts and Chaparral

  • Seed plants in the desert produce seeds that can remain in dormancy for extended periods between rains.
  • The chaparral vegetation is dominated by shrubs and is adapted to periodic fires, with some plants producing seeds that only germinate after a hot fire .
  • Some plants produce seeds that only germinate after a hot fire.

• Auxins, Cytokinins, and Gibberellins

  • Gibberellins (GAs) are a group of about 125 closely-related plant hormones that stimulate shoot elongation, seed germination, and fruit and flower maturation.
  • GAs are synthesized in the root and stem apical meristems, young leaves, and seed embryos.
  • GAs break dormancy (a state of inhibited growth and development) in the seeds of plants that require exposure to cold or light to germinate.
  • Seedless grapes are obtained through standard breeding methods; they contain inconspicuous seeds that fail to develop.
  • Because GAs are produced by the seeds and because fruit development and stem elongation are under GA control, these varieties of grapes would normally produce small fruit in compact clusters.

• Angsiosperm Fruit

  • A fertilized, fully grown, and ripened ovary containing a seed forms what we know as fruit, important seed dispersal agents for plants.
  • As the seed develops, the walls of the ovary in which it forms thicken and form the fruit, enlarging as the seeds grow.
  • Regardless of how they are formed, fruits are an agent of seed dispersal.
  • Once eaten, tough, undigested seeds are dispersed through the herbivore's feces.
  • The winged shape of Alsomitra macrocarpa's seeds allow them to use wind for dispersal.

• Agricultural Diversity

  • Sometimes, however, seed banks are lost through accidents; there is no way to replace them.
  • In 2008, the Svalbard Global Seed Vault began storing seeds from around the world as a backup system to the regional seed banks .
  • If a regional seed bank stores varieties in Svalbard, losses can be replaced from those stored here.
  • The seed vault is located deep into the rock of an arctic island.
  • The Svalbard Global Seed Vault is a protected storage facility in the arctic for seeds of earth's diverse crops.

• Evolution of Gymnosperms

  • Seed ferns gave rise to the gymnosperms during the Devonian Period, allowing them to adapt to dry conditions.
  • The fossil plant Elkinsia polymorpha, a "seed fern" from the Devonian period (about 400 million years ago) is considered the earliest seed plant known to date.
  • Seed ferns produced their seeds along their branches without specialized structures .
  • What makes them the first true seed plants is that they developed structures called cupules to enclose and protect the ovule (the female gametophyte and associated tissues) which develops into a seed upon fertilization.
  • This gave a reproductive edge to seed plants, which are better adapted to survive dry spells.

• The Major Divisions of Land Plants

  • Land plants, or embryophytes, are classified by the presence or absence of vascular tissue and how they reproduce (with or without seeds).
  • Lycophytes and pterophytes are both referred to as seedless vascular plants because they do not produce any seeds.
  • The seed producing plants, or spermatophytes, form the largest group of all existing plants, dominating the landscape.
  • Seed-producing plants include gymnosperms, most notably conifers, which produce "naked seeds," and the most successful of all modern-day plants, angiosperms, which are the flowering plants.
  • Land plants are categorized by presence or absence of vascular tissue and their reproduction with or without the use of seeds.