Halophytes providing food and shelter for a range of

Halophytes are salt-tolerant plant species,
provide multiple benefits. This group of plants has the ability to survive
salinity, drought and other harsh conditions in both temperate and tropical
climates, and in a very wide range of environments from hot deserts to tundra. They
play a key role in the ecosystem, protecting habitats, maintaining ecological
stability, preventing soil erosion and seawater intrusion into freshwater
habitats, and providing food and shelter for a range of fauna. Halophytes also
represent an important source of novel genes to enhance drought and salinity
tolerance in crop varieties. Halophytes also have huge potential to aid
agricultural development and habitat restoration in areas affected by salinity.
However, Most halophytes produce salt-free seeds, which require freshwater and
temperatures greater than 13°C in order to germinate; but there are exceptions
that can germinate at sea water
concentrations ( Al-Oudat & Qadir, 2011).

Halophytes have developed different strategies
to survive the very high salt concentration in soil water depending on their habitat
conditions. They are categorized into obligatory that need some salt and
facultative halophytes that can also grow under freshwater conditions depending
on their tolerance and demand for sodium salts. Other categories of halophytes
are: Hydro-halophytes that grow in aquatic conditions or on wet soils (most
mangroves such as Avicennia marina), and Xero-halophytes
that may grow in habitats where the soil is always saline but where the soil
may dry out so much as to cause problems of
plant water availability ( Al-Oudat & Qadir, 2011).

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Marine halophytes can grow in extreme
locations, such as salt marshes, characterized by several abiotic constraints
like high salinity, drought, heat, cold and luminosity. To tolerate those
conditions these plants are equipped with potent antioxidant systems comprised
by enzymes and highly bioactive secondary metabolites, such as phenolic
compounds and alkaloids, with established beneficial therapeutic effects in
humans. Several marine halophytes are traditionally used for nutritional and
medicinal purposes. For example, Chenopodium quinoa (quinoa) is known for its
high nutritional value while Salicornia L. species (sea asparagus) are
highly valued in gourmet cuisine and used in traditional medicine against
chronic diseases, as for example diabetes and cancer (Lopes et al., 2016).

Stress response mechanisms in halophytes have
been affects cellular membranes, enzyme activities and the photosyntethic system, is largely caused by the damage from
the production of reactive oxygen species (ROS). Therefore, Plants have evolved
two antioxidative pathways to combat damage from ROS: an enzymatic pathway,
which involves enzymes such as super oxide
dismutase, and catalase, and a nonenzymatic pathway which includes antioxidants
such as tocopherol, carotenoids, ascorbate, phenolic compounds, alkaloids,
glutathione and non-protein amino acids that scavenge free radicals (Cybulska
et al., 2014).

Halophyte metabolites are a combination of
components typical for lignocellulosic biomass and components unique for a
family or species. The most commonly found components include primary
metabolites such as amino acids, protein, carbohydrates and lignin. Secondary metabolites or phytochemicals include compounds
of pharmacological and biological importance, such as alkaloids, fatty acids and lipids, flavonoids, phenolics, quinines,
tannins, terpenoids, steroids and saponins, coumarins to name a few. Content of the secondary metabolites can vary
depending on the particular habitat where the plant grows (Cybulska et al.,
2014). Although a number of publications have focused on the isolation and
identification of bio-active compounds, it is important to keep in mind the
complexity of plants and a single compound may not be responsible for the
observed activity but rather a combination of either major or minor compounds
interacting in an additive or synergistic manner (Vuuren,
2008).

Halophytic plants contain variable amounts of
secondary metabolites, these compounds are of most interest because they are
often specific to a particular plant species or genus and must therefore have
been designed to serve a particular protective function. For example, compounds
such as terpenes, numerous classes of phenolics, steroids, cyanogenic compounds
and alkaloids (Gihad & ElShaer, 1994). Some of The halophytic plants
differed in their capacity to accumulate phenolic compounds, even if they grew
in the same environment, experiencing the same stressful conditions; they
produced different patterns of total phenols (Meot-Duros et al., 2008).

Bandaranayake (2002) mentioned Some example of
the use of halophytes plants that contain bioactive compounds,  Acanthus illicifolius, a plant useful
in the treatment of paralysis, asthma, rheumatic pains and possessing
analgesic, anti-inflammatory and, leishmanicidal activities, is a rich source
of long chain alcohols, triterpenes, steroids and triterpenoidal saponins.
Stigmasterol, a common plant steroid, abundantly present in A. illicifolius
and many other mangrove plants, has been shown to have hypercholesterolemic effects.
2-Benzoxazoline, a synthetic compound used extensively as a central nervous
system depressant, also exhibiting antipyretic, hypnotic, and muscle relaxant
activity has been isolated from the plant. Benzoxazoline also showed resistance
to fungi, and the ribose derivatives of this compound are active as anticancer
and anti-viral agents. Benzoquinones have been identified from Aegicers
corniculatum and Kandelia candel.
Decoctions made from the rhizome of the reed grass Arundo donax has been
used as emollients and diuretics and are said to stimulate menstrual discharge
and diminish secretion of milk, triterpenes, sterols, alkaloids, and the novel
compound, N-(4′-bromophenyl)-2,2- diphenylacetanilide, hitherto known only as a
synthetic compound, has been isolated from different parts of this plant
(Bandaranayake, 2002).

Owing to global climate change, salinisation of
soils is becoming a more and more serious threat for agriculture. Therefore salt tolerant plants could serve as the
crop plants of the future. So far, few halophytes have been exploited for their
potential to be grown as crop plants. Salt tolerance of halophytes relies on
several strategies, among them, the production of species-specific secondary
metabolites. Chemically, a broad variety of secondary compounds of economic
interest is present in halophytes. Several of these secondary compounds are
restricted to halophytic species or are found in higher concentrations than in
glycophytes. Also, different plant organs and plants in different developmental
stages contain highly varying amounts and compositions of secondary compounds.
Secondary compounds from halophytes have potential uses in various fields such
as pharmacognosy, functional foods, nutraceuticals and technical
implementations (Buhmann &
Papenbrock, 2013).

Halophytic plants can be grown not only for
food and fuel but also for medicinal purposes. In traditional medicine some
species play an important role in treating diseases in different parts of the
world. For example, Ipomoea pes-caprae contain many biologically active
constituents such as alkaloids, phenolics, coumarins, flavonoids etc. and show
analgesic, antimicrobial, and anticoagulant properties, is used to treat
fatigue, strain, arthritis, and rheumatism. T. catappa leaf is used to
treat liver disease in Taiwan and in India it is used as a cardiac stimulant,
for treating dermatosis and hepatitis, and has shown better antibacterial
activity than some commercially used antibacterial agents. Mesembryanthemum
crystallinum is used for its polyol-rich food which is known to have
disease-preventing functions. In addition to being used as a fuelwood, Tamarix
gallica has bioactive compounds such as phenols, glycosides, tannins,
flavonoids, steroids, saponins, and alkaloidsandis
often used for treatment of liver disease
in traditional medicine. The phenolic compound from
this species is known for its anti-aging, anti-inflammatory and
anti-carcinogenic properties. The facultative halophyte C. mar-itimum, also known as crest marine or
marine fennel, has been largely used for nutritional and medicinal purposes as
it is rich in several bioactive substances, minerals, vitamin C, essential oils
and other biomolecules (Panta et al., 2014).

Panta et al
(2014) Argue that the use of halophytes may be a viable commercial alternative
to ease pressure on the requirement of good quality land and water for
conventional cropping systems and the utilization of land degraded by salinity.
Also of interest is the fact that there have been several new halophyte
species described recently in the Gulf region, and as of yet there have been no
studies on the phytochemical content of these species. Phytochemicals have been
found in closely related species, indicating that these new species may also be
a source of useful compounds (Cybulska et al., 2014)