desiccation tolerance

Examples of desiccation tolerance in the following topics:

• Plant Adaptations to Life on Land

  • Desiccation, or drying out, is a constant danger for organisms exposed to air.
  • As such, both gametes and zygotes must be protected from desiccation.
  • One of these strategies is called desiccation tolerance.
  • Later, plants moved away from moist or aquatic environments and developed resistance to desiccation, rather than tolerance.
  • The vulnerable embryo must be sheltered from desiccation and other environmental hazards.

• Bryophytes

  • They constitute the major flora of inhospitable environments like the tundra where their small size and tolerance to desiccation offer distinct advantages.

• The Evolution of Seed Plants and Adaptations for Land

  • Several layers of hardened tissue prevent desiccation, freeing reproduction from the need for a constant supply of water.
  • Furthermore, seeds remain in a state of dormancy induced by desiccation and the hormone abscisic acid until conditions for growth become favorable.
  • The whole structure is protected from desiccation and can reach the female organs without dependence on water.

• Zygomycota: The Conjugated Fungi

  • The developing diploid zygospores have thick coats that protect them from desiccation and other hazards.

• Regulating Immune Tolerance

  • Immune tolerance of self and harmless antigens occurs by deleting B and T cells that recognize those antigens, often near mucosal surfaces.
  • The acquired ability to prevent an unnecessary or harmful immune response to a detected foreign substance known not to cause disease or to self-antigens is described as immune tolerance.
  • The primary mechanism for developing immune tolerance to self-antigens occurs during the selection for weakly, self-binding cells during T and B lymphocyte maturation.
  • Immune tolerance is especially well developed in the mucosa of the upper digestive system because of the tremendous number of foreign substances (such as food proteins) that APCs of the oral cavity, pharynx, and gastrointestinal mucosa encounter.
  • Immune tolerance is brought about by specialized APCs in the liver, lymph nodes, small intestine, and lung that present harmless antigens to a diverse population of regulatory T (Treg) cells: specialized lymphocytes that suppress local inflammation and inhibit the secretion of stimulatory immune factors.

• Osmoregulators and Osmoconformers

  • Aquatic organisms with various salt tolerances adapt to their environments through osmoregulation and osmoconformation.
  • Stenohaline organisms, such as goldfish, can tolerate only a relatively-narrow range of salinity.
  • These organisms, such as the salmon, are tolerant of a relatively-wide range of salinity.

• Physical and Chemical Barriers

  • Pathogens are killed or inactivated on the skin by desiccation (drying out) and by the skin's acidity.

• Marine Biomes

  • The exoskeletons of shoreline crustaceans are tough, protecting them from desiccation and wave damage.

• Liverworts and Hornworts

  • The plant takes up water over its entire surface and has no cuticle to prevent desiccation.

• Fungi Cell Structure and Function

  • The wall protects the cell from desiccation and predators.