Halotolerance
Encyclopedia
Halotolerance is the adaptation of living organism
s to conditions of high salinity
. Halotolerant species tend to live in areas such as hypersaline lake
s, coastal dunes
, saline desert
s, salt marsh
es, and inland salt sea
s and spring
s. Halophile
s are a group of bacteria that live in highly saline environments, and indeed in many cases require the salinity to survive. Halophyte
s are salt-tolerant higher plants.
, molecular biology
, cell biology
, physiology
, ecology
, and genetics
.
An understanding of halotolerance can be applicable to areas such as arid-zone agriculture
, xeriscaping
, aquaculture
(of fish or algae), bioproduction of desirable compounds (such as phycobiliprotein
s or carotenoid
s) using seawater to support growth, or remediation of salt-affected soils. In addition, many environmental stressors involve or induce osmotic changes, so knowledge gained about halotolerance can also be relevant to understanding tolerance to extremes in moisture or temperature.
Goals of studying halotolerance include increasing the agricultural productivity of lands affected by soil salination
or where only saline water is available. Conventional agricultural species could be made more halotolerant by gene transfer from naturally halotolerant species (by conventional breeding
or genetic engineering
) or by applying treatments developed from an understanding of the mechanisms of halotolerance. In addition, naturally halotolerant plants or microorganisms could be developed into useful agricultural
crops or fermentation
organisms.
must show methods of balancing the toxic and osmotic effects of the increased salt concentrations. Halophytic vascular plants can survive on soils with salt concentrations around 6%, or up to 20% in extreme cases. Tolerance of such conditions is reached through the use of stress proteins and compatible cytoplasm osmotic solutes.
To exist in such conditions, halophytes tend to be subject to the uptake of high levels of salt into their cells, and this is often required to maintain an osmotic potential lower than that of the soil to ensure water uptake. High salt concentrations within the cell can be damaging to sensitive organelles such as the chloroplast, so sequestration of salt is seen. Under this action, salt is stored within the vacuole
to protect such delicate areas. If high salt concentrations are seen within the vacuole, a high concentration gradient will be established between the vacuole and the cytoplasm, leading to high levels of energy investment to maintain this state. Therefore, the accumulation of compatible cytoplasmic osmotic solutes can be seen to prevent this situation from occurring. Amino Acids such as proline accumulate in halophytic Brassica
species, quaternary ammonium bases such as Glycine Betaine and sugars have been shown to act in this role within halophytic members of Chenopodiaceae
and members of Asteraceae
show the build up of cyclites and soluble sugars. The build up of these compounds allow for the balancing of the osmotic effect while preventing the establishment of toxic concentrations of salt or requiring the maintenance of high concentration gradients.
in Botswana
.
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
s to conditions of high salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
. Halotolerant species tend to live in areas such as hypersaline lake
Hypersaline lake
A hypersaline lake is a landlocked body of water that contains significant concentrations of sodium chloride or other mineral salts, with saline levels surpassing that of ocean water . Specific microbial and crustacean species thrive in these high salinity environments that are otherwise...
s, coastal dunes
Dune
In physical geography, a dune is a hill of sand built by wind. Dunes occur in different forms and sizes, formed by interaction with the wind. Most kinds of dunes are longer on the windward side where the sand is pushed up the dune and have a shorter "slip face" in the lee of the wind...
, saline desert
Desert
A desert is a landscape or region that receives an extremely low amount of precipitation, less than enough to support growth of most plants. Most deserts have an average annual precipitation of less than...
s, salt marsh
Marsh
In geography, a marsh, or morass, is a type of wetland that is subject to frequent or continuous flood. Typically the water is shallow and features grasses, rushes, reeds, typhas, sedges, other herbaceous plants, and moss....
es, and inland salt sea
Sea
A sea generally refers to a large body of salt water, but the term is used in other contexts as well. Most commonly, it means a large expanse of saline water connected with an ocean, and is commonly used as a synonym for ocean...
s and spring
Spring (hydrosphere)
A spring—also known as a rising or resurgence—is a component of the hydrosphere. Specifically, it is any natural situation where water flows to the surface of the earth from underground...
s. Halophile
Halophile
Halophiles are extremophile organisms that thrive in environments with very high concentrations of salt. The name comes from the Greek for "salt-loving". While the term is perhaps most often applied to some halophiles classified into the Archaea domain, there are also bacterial halophiles and some...
s are a group of bacteria that live in highly saline environments, and indeed in many cases require the salinity to survive. Halophyte
Halophyte
A halophyte is a plant that grows where it is affected by salinity in the root area or by salt spray, such as in saline semi-deserts, mangrove swamps, marshes and sloughs, and seashores. An example of a halophyte is the salt marsh grass Spartina alterniflora . Relatively few plant species are...
s are salt-tolerant higher plants.
Applications
Fields of scientific research relevant to halotolerance include biochemistryBiochemistry
Biochemistry, sometimes called biological chemistry, is the study of chemical processes in living organisms, including, but not limited to, living matter. Biochemistry governs all living organisms and living processes...
, molecular biology
Molecular biology
Molecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...
, cell biology
Cell biology
Cell biology is a scientific discipline that studies cells – their physiological properties, their structure, the organelles they contain, interactions with their environment, their life cycle, division and death. This is done both on a microscopic and molecular level...
, physiology
Physiology
Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...
, ecology
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
, and genetics
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
.
An understanding of halotolerance can be applicable to areas such as arid-zone agriculture
Arid-zone agriculture
As an area of research and development, arid-zone agriculture, or desert agriculture, includes studies of how to increase the agricultural productivity of lands dominated by lack of freshwater, an abundance of heat and sunlight, and usually one or more of extreme winter cold, short rainy season,...
, xeriscaping
Xeriscaping
Xeriscaping and xerogardening refers to landscaping and gardening in ways that reduce or eliminate the need for supplemental water from irrigation...
, aquaculture
Aquaculture
Aquaculture, also known as aquafarming, is the farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the...
(of fish or algae), bioproduction of desirable compounds (such as phycobiliprotein
Phycobiliprotein
Phycobiliproteins are water-soluble proteins present in cyanobacteria and certain algae that capture light energy, which is then passed on to chlorophylls during photosynthesis. Phycobiliproteins are formed of a complex between proteins and covalently bound phycobilins that act as chromophores...
s or carotenoid
Carotenoid
Carotenoids are tetraterpenoid organic pigments that are naturally occurring in the chloroplasts and chromoplasts of plants and some other photosynthetic organisms like algae, some bacteria, and some types of fungus. Carotenoids can be synthesized fats and other basic organic metabolic building...
s) using seawater to support growth, or remediation of salt-affected soils. In addition, many environmental stressors involve or induce osmotic changes, so knowledge gained about halotolerance can also be relevant to understanding tolerance to extremes in moisture or temperature.
Goals of studying halotolerance include increasing the agricultural productivity of lands affected by soil salination
Soil salination
Soil salinity is the salt content in the soil.- Causes of soil salinity :Salt-affected soils are caused by excess accumulation of salts, typically most pronounced at the soil surface. Salts can be transported to the soil surface by capillary transport from a salt laden water table and then...
or where only saline water is available. Conventional agricultural species could be made more halotolerant by gene transfer from naturally halotolerant species (by conventional breeding
Artificial selection
Artificial selection describes intentional breeding for certain traits, or combination of traits. The term was utilized by Charles Darwin in contrast to natural selection, in which the differential reproduction of organisms with certain traits is attributed to improved survival or reproductive...
or genetic engineering
Genetic engineering
Genetic engineering, also called genetic modification, is the direct human manipulation of an organism's genome using modern DNA technology. It involves the introduction of foreign DNA or synthetic genes into the organism of interest...
) or by applying treatments developed from an understanding of the mechanisms of halotolerance. In addition, naturally halotolerant plants or microorganisms could be developed into useful agricultural
Agriculture
Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...
crops or fermentation
Fermentation (biochemistry)
Fermentation is the process of extracting energy from the oxidation of organic compounds, such as carbohydrates, using an endogenous electron acceptor, which is usually an organic compound. In contrast, respiration is where electrons are donated to an exogenous electron acceptor, such as oxygen,...
organisms.
Cellular functions
Tolerance of high salt conditions can be obtained through several routes. High levels of salt entering the plant can trigger ionic imbalances which cause complications in respiration and photosynthesis, leading to reduced rates of growth, injury and death in severe cases. To be considered tolerant of saline conditions, the protoplastProtoplast
Protoplast, from the ancient Greek πρῶτον + verb πλάθω or πλάττω , initially referred to the first organized body of a species.Protoplast has several biological definitions:...
must show methods of balancing the toxic and osmotic effects of the increased salt concentrations. Halophytic vascular plants can survive on soils with salt concentrations around 6%, or up to 20% in extreme cases. Tolerance of such conditions is reached through the use of stress proteins and compatible cytoplasm osmotic solutes.
To exist in such conditions, halophytes tend to be subject to the uptake of high levels of salt into their cells, and this is often required to maintain an osmotic potential lower than that of the soil to ensure water uptake. High salt concentrations within the cell can be damaging to sensitive organelles such as the chloroplast, so sequestration of salt is seen. Under this action, salt is stored within the vacuole
Vacuole
A vacuole is a membrane-bound organelle which is present in all plant and fungal cells and some protist, animal and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic molecules including enzymes in solution, though in certain...
to protect such delicate areas. If high salt concentrations are seen within the vacuole, a high concentration gradient will be established between the vacuole and the cytoplasm, leading to high levels of energy investment to maintain this state. Therefore, the accumulation of compatible cytoplasmic osmotic solutes can be seen to prevent this situation from occurring. Amino Acids such as proline accumulate in halophytic Brassica
Brassica
Brassica is a genus of plants in the mustard family . The members of the genus may be collectively known either as cabbages, or as mustards...
species, quaternary ammonium bases such as Glycine Betaine and sugars have been shown to act in this role within halophytic members of Chenopodiaceae
Chenopodiaceae
Chenopodiaceae were a family of flowering plants, also called the Goosefoot Family. They are now included within family Amaranthaceae. The vast majority of Chenopods are weeds, and many are salt and drought tolerant. A few food crops also belong to the family: spinach, beets, chard, quinoa, and...
and members of Asteraceae
Asteraceae
The Asteraceae or Compositae , is an exceedingly large and widespread family of vascular plants. The group has more than 22,750 currently accepted species, spread across 1620 genera and 12 subfamilies...
show the build up of cyclites and soluble sugars. The build up of these compounds allow for the balancing of the osmotic effect while preventing the establishment of toxic concentrations of salt or requiring the maintenance of high concentration gradients.
Bacterium halotolerance
The extent of halotolerance varies widely amongst different species of bacteria. A number of cyanobacteria are halotolerant; an example location of occurrence for such cyanobacteria is in the Makgadikgadi Pans, a large hypersaline lakeHypersaline lake
A hypersaline lake is a landlocked body of water that contains significant concentrations of sodium chloride or other mineral salts, with saline levels surpassing that of ocean water . Specific microbial and crustacean species thrive in these high salinity environments that are otherwise...
in Botswana
Botswana
Botswana, officially the Republic of Botswana , is a landlocked country located in Southern Africa. The citizens are referred to as "Batswana" . Formerly the British protectorate of Bechuanaland, Botswana adopted its new name after becoming independent within the Commonwealth on 30 September 1966...
.