A large number of herbal
plants are widely used for their medicinal properties and more dependency on
these plants has led to the loss of natural bioresources which is leading
towards the extinction of plant species. Factors such as increase in the human
population, urbanization and increased industrialization also lead to the
exploitation of bioresources. Supply of herbal plants is also hampered due to
decrease in the population of plant species. A lot of time is needed for the
building of commercial quantities of selected clones. Plant tissue culture has
been emerging as an important technique for the rapid multiplication of large
number of medicinally important plants at a large scale under laboratory
conditions. This technique involves production of plantlets from the small
portions of living tissues also termed as explants on artificial culture medium
under controlled aseptic conditions. The production of plantlets in the in vitro conditions is termed as
micropropagation where the whole plant is produced from the small parts that
can be nodes, meristems, shoot tips, anthers etc. A large number of commercial
plants have been propagated by this technique on different culture mediums that
can be auxins, cytokinins etc.( Preil, 2003; Rou and Jain, 2004).The advantages
of the in vitro micropropagation are
the mass production of plants in a short time period with high uniformity, the
species which are getting endangered and are considered rare can be conserved,
a large quantity of genetically identical plants can be produced, desired
plants with traits such as flowers, color, odours etc. can be produced,
disease-free plantlets can be grown, regeneration of whole plants from
genetically modified plant cells can be done. The objective of using culturing
techniques is to obtain many active secondary metabolites, like some important
active compounds for pharmaceuticals and cosmetics, enzymes, proteins,
hormones, food additives etc. (Terrier et
al., 2007). The success rate of the micropropagation is dependent on the
culture medium, genotype and the controlled culture conditions. Several studies
regarding in vitro stem or shoot
multiplication via direct organogensis of Withania
somnifera have been reported. (Kulkarni et
al., 2000; Govindaraju et al,
2003 and Naveen Gaurav et al., 2015).
In vitro flowering and rapid
propagation of Physalis minima has
also been reported. (Sheeba et al.,
2015). Several studies on Datura species have been done such as in vitro propagation of Datura innoxia from nodal and shoot tip
explants. ( Ashwini et al., 2013). Studies
on In vitro micropropagation of Datura metel L. through somatic embryos
from root explants (Nithiya and Arockiasamy, 2007) have been done.

In vitro micropropagation of
medicinal plants:







Many members of
solanaceae family exhibit good antioxidant potential to curb diseases.
Ethanolic and methanolic leaf extracts show good in vitro antioxidant activity.

With time being, people
have shown the increased interest in medicinal plants as they have good
therapeutic potential, are less toxic, strong antioxidant potential, they are
distributed widely and have many medicinal properties. Medicinal plants possess
various phytochemicals such as flavonoids, terpenoids, alkaloids and phenolic
compounds which possess strong antioxidant activity protecting cells from
oxidative damage caused by free radicals.( Krishnaiah, et al; 2011). Antioxidant defense mechanism is the most effective
path for eliminating the free radicals. Antioxidants can prevent the chain
initiation by scavenging the radicals, they can decompose the peroxides into
non radicals thorough conversion, decompose the lipid peroxides into alkoxyl
and peroxyl radicals and brake the chain elongation preventing hydrogen
abstraction.( Miguel, 2010). Antioxidants are functional in protecting against
harmful diseases as they prevent injury to the blood membranes, they can lower
the risk of Alzheimer’s disease, show optimization in the blood flow to the
heart and brain and prevent the damage of DNA. (Ames et al.,1993). Protective compounds can inhibit the formation of
reactive oxygen species (ROS), they can scavenge the free radicals and chelate
the metals. (Panteleon et al; 2008).
People are becoming increasingly interested in medicinal plants because of
their strong antioxidant activities, good therapeutic performance and low
toxicity, wide distributions and medicinal functions.  Interest in the plants for their antioxidant
potential has increased with time being because they reduce the function of
free radicals. For the search on antioxidant potential, many plants have been
studied. (Chu, 2000; Koleva et al.,
2002, Mantle et al., 2000; Oke and
Hamburger, 2002), there is still a greater demand regarding the potential of
plants serving as antioxidants. Many phenolic compounds which are the secondary
metabolites of plants possess show antioxidant potential including phenols and
flavonoids. Phenolic compounds act as the hydrogen donors, metal chelators,
singlet oxygen quenchers and radical scavengers. (Proestos et al., 2006). Flavonoids have functional hydroxyl groups which
show antioxidant activity of chelating the metal ion and free radical
scavenging. (Kumar et al.,2013. Chelation
of metal ions prevents the formation of the radicals which damages the
biomolecules. (Leopoldini, 2006 and Kumar et
al., 2013).

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Free radicals are the
powerful oxidant species containing unpaired electrons and are capable of
modifying the biomolecules causing many health problems. Free radicals are
produced as a result of production of ATP by mitochondria that can be singlet
oxygen, super oxide, peroxyl radicals or hydroxyl radicals resulting in
oxidative stress that leads to the cellular damage. (Mattson & Cheng,
2006). Oxidative stress occurs due to the imbalance occurring between the
antioxidants and oxidants that favour the oxidants leading to the damage. Free
radicals have the tendency to trap the electron from the molecules of their
surroundings and if they are not scavenged, they can damage many biomolecules
such as proteins, lipids, mitochondria and DNA causing many abnormalities and
serious diseases. (Uddin et al,
2008). They can cause many harmful diseases such as artherosclerosis,
infertility, tumour inflammation, asthma, cardiovascular disorders, hemorraghic
shock, AIDS, rheumatoid arthritis, cystic fibrosis, gastroinstestinal
ulcerogenesis and many more. (Chen et al.,
2006 ; Uddin et al., 2008).

Antioxidant activity of medicinal plants:


Glycosides are the class
of secondary metabolites which are the condensed products of many sugars that
can be polysaccharides having different varieties of organic hydroxyl thiol
compounds. Glycosides consist of a carbohydrate part (sugar) and a
non-carbohydrate part also called aglycone.(Kar, 2007′ Firn, 2010). Digitoxin
from digitalis, cantharidin from Cantharides, Salicin from salix and prunasin
from prunus are some examples of plant glycosides. They are classified under
cardiac glycosides, anthracene glycosides and many more. Many cyanogenic
glycosides are used in pharmaceutical preparations as flavouring agents.
Amygdalin found from the plants is used as a cough suppressant and for treating
cancer. Anthracene derivatives formed from the plants are used as cathartics.
Glucosinolates, the constituents obtained from the members of Brassicaceae
family possess anticarcinogenic properties. Medicinally the glycosides exhibit
laxative, analgesic, anti-inflammatory and anti-fungal properties.



Saponins are the class of
secondary metabolites occurring in the plants and are known as detergents or
natural surfactants. Most of the extracts of plants that contain saponins are
widely used for many commercial applications like for the separation of ores in
mining and in industry. Most of them form the products in shampoos, cosmetics
and photographic emulsions. Saponins show antibacterial and anti-fungal
properties and have positive effects in lowering the level of cholesterol in
blood and in many cases inhibit growth of cancer cells. Digitalis, known as a
saponin is considered effective in strengthening the heart muscle contraction,
so it is very good to cure heart disease. Saponins show anticancerous and
hypolipidemic properties and many steroidal saponins are commercially used in
the production of sex hormones for their use in clinics. (Blundenet et al.,1975). Some are used as drugs
(Panacos, 2005) and as immunological adjuvants. (Kensil et al.,2004). Saponins inhibit the cell proliferation of tumour
cells (Gauthier et al.,2011), lower
the levels of triacylglycerol( Megalli et
al.,2006), have cytotoxic properties, show anti-platelet aggregation.(Huang
et al; 2006) and exhibit haemolytic
activity.(Gauthier et al; 2009; Tava et al., 2009).



Plant steroids are termed
as cardiac glycosides and occur naturally in the plants as phytoconstituents
known for their therapeutic properties like cardiac drugs or arrow poisons. (Firn,
2010). The cardiac steroids have ability to show a powerful action on the
cardiac muscles when they are administered into humans or animals in the form
of injections. Some anabolic steroids have the property of promoting retention
of nitrogen in case of osteoporosis and in case of animals with illness. (Maurya
et al.,2008 and Madziga et al., 2010).


Terpenoids are considered
as the largest group among the phytochemicals and are the class of active
secondary metabolites which are made up of isoprene (C5) units and
show a large diversification in their structures and biological activities. The
terpenoids derived from the plants are aromatic in nature and used widely for
their aromatic qualities. They are classified as –Monoterpenoids, sesquterpenoids
and triterpenoids. They play a vital role in plant defense mechanism and are
beneficial to humans for their anti-viral, anti-oxidant, anti-cancerous,
anti-inflammatory, anti-fungal, anti-spasmodic, anti-hyperglycemic and immuno-modulatory
properties.( Rabi, 2009; Wagner, 2003; Sultana 2008 and Shah et al; 2009). They are also used
extensively for the storage of agricultural products as they possess
insecticidal properties. (Theis and Lerdau, 2003). Monoterpenes possess
properties of treating cancers of skin, lung, colon, prostate, pancreatic,
mammary and stomach. (Kris-Etheron et al.,2002;
Gould, 1997, Reddy et al.,1997;Vigushin
et al.,1998 and Crowell, 1999).



Phenolic compounds are
distributed most widely among the plant secondary metabolites and higher plants
constitute the highest number of phenolic compounds. Phenols basically have a
phenyl ring which bears one or more number of hydroxyl substitutes. They are
classified on the basis of number of carbon atoms that are present in the
molecules. (Harborne and Simmonds, 1964). These compounds play a very crucial
role in the growth and reproduction of plants and they are released in response
to pollution, light and many other factors. (Valentine et al., 2003). Phenolic compounds not only play an important part
in the plant’s defense mechanism but they are effective in eradicating many
human aliments. They are proved to be the good antioxidants because of their
scavenging activities as they scavenge the ROS/RNS( reactive nitrogen species)
by inhibiting some of the enzymes and have the property of chelation as they
chelate some trace metals which form free radicals thereby upgrading the
antioxidant defense mechanism.( Cotelle, 2001).Phenolic compounds show many
physiological properties that include anti-inflammatory, anti-thrombotic,
anti-artherogenic, cardioprotective, anti-allergenic, vasodilatory effects and
anti-microbial properties.(Manach et al.,
2005; Middleton et al., 2000 and
Puupponen-Pimia et al., 2001).


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