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INTRODUCTION
INTRODUCTION
Fenugreek (Trigonella foenum-graecum L.) is an annual herb belonging to the
family Fabaceae and grown widely in India, Pakistan, Egypt and Middle Eastern
countries (Alarcon-Aguilara et al., 1998). The major states growing fenugreek in India
are Rajasthan, Gujrat, Madhya Pradesh, Maharashtra, Haryana, Punjab, Bihar and
Andhra Pradesh (Mehta et al., 2010). India happens to be the largest producer,
consumer and exporter of spices in the world. Fenugreek routinely known as ‘methi’
occupies an important place among the various spices grown in country with respect to
area as well as production (Kaushik, 2011).
Leaves and seeds of fenugreek are included in normal diet of family, especially
diet of growing kids, pregnant ladies, puberty reaching girls and elder members of
family because of their haematinic value (Ody, 1993). Legumes are functional foods
having therapeutic properties and promoting good health (Geil and Anderson, 1994 see
Madar and Stark, 2002 also). Methi was used to ease childbirth and to increase milk
flow, and modern Egyptian women are still using it to relieve menstrual cramps. The
Chinese call it hu lu ba, and also use it to ease abdominal pain. This cool season crop is
grown in most corners of the world, however, awareness about its value and uses vary
considerably. In India, fresh methi ka saag (the stems and leaves of the plant) is a very
common winter vegetable, and the seeds are used year round as a flavouring agent for
various dishes whereas, it is not so well known in west. The leaves of methi rich in iron,
calcium, sulphur and vitamins A and C and are highly alkaline. They possess as much
protein as most pulses do, and therefore can substitute for other sources of protein
(Passano, 1995). Fenugreek possesses restorative and nutritive properties and is useful
in healing of ulcers in digestive tract stimulating digestive processes (Khosla et al.,
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1995). Strong flavor and aroma of the leaves and seeds of fenugreek are possibly
responsible for its consumption as spice in oriental countries. Fenugreek is a rich source
of calcium, iron, ß-carotene and other vitamins (Sharma et al., 1996). Fenugreek
exhibits antitumor, antiviral, antimicrobial, anti-inflammatory and antioxidant
properties (Cowan, 1999). Legumes are low in Na and are good source of starch, dietary
fibre, protein and minerals such as Ca, Fe, K, Mg and Zn and are containing no
cholesterol (Madar and Stark, 2002). Fenugreek is used as a green manure and
renovates soil (Abdelgani et al., 1999). Fenugreek grows well in moderately cool
climate in all types of soils with good drainage and has greater salinity tolerance in
comparison to other leguminous crops (Leela and Shafeekh, 2008).
In Indian soil potassium is a limiting nutrient next to nitrogen and phosphorus
(Sekhon and Ghosh, 1982). In plants potassium is linked with plant growth, movement
of water, nutrients and carbohydrates (Rehm and Schmitt, 1997). Crops need potassium
and nitrogen in fairly comparable amounts nevertheless, routinely the balance is not
observed (Radulov, 2004). Potassium is a multifunctional and mobile element
influencing directly and indirectly various biochemical and physiological processes
(Radulov et al., 2012).
Magen (2008) has focused on the need of balanced and timely application of
nutrients in prevailing agro-climatic conditions otherwise pointing out the decrease in
soil fertility and stagnating and reduced productivity due to negative K balance.
However, balanced nutrient supply is required as application of potassium in certain
cases may lead to depressed yield if nitrogen and phosphorus are not sufficient (Tisdale
et al., 1990 and Bajwa and Rehman, 1996). Potassium fertilizers increased yield in
maize (Heckman and Kamprath, 1992; Mallarino et al., 1999 and Ebelhar and Varsa,
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2000). Sweeney et al. (2000) have reported potassium fertilizers to regulate wheat
growth and increase grain yield and reduce leaf rust. Greater plant vigor was obtained
by potassium fertilizers contributing in grain filling and in the production of stronger
wheat straw (Shen et al., 1998 and Nawab et al., 2006).
Potassium deficiency decreased translocation at light intensities not affecting
rate of photosynthesis due to potassium levels and even at light intensities not effective
for net fixation of carbon dioxide (Hartt, 1970). Potassium treatments also improved dry
matter and total nitrogen content in faba bean plants subjected to restricted water supply
during post flowering period probably by promoting the growth and not by enhancing
the nitrogen fixation efficiency (Kurdali et al., 2002).
Supplementation of potassium to the nutrient solution mitigates the negative
effect of NaCl on growth and grain yield of barley by improving nitrogen uptake and
nitrogen metabolism (Helal et al., 1975). Addition of potassium salts to the growth
medium alleviated NaCl toxicity by increasing potassium content of plants in bean and
sunflower (Benlloch et al., 1994), tomato (Satti and Lopez, 1994) and maize (Botella et
al., 1997). Foliar spray of K2SO4 counteracted salt-induced inhibition in growth and
yield of rice plants (Din et al., 2001). Foliar application of potassium salts on tomato
counteracts drought induced detrimental effects on plant growth and salinity induced
membrane damage (Kaya et al., 2001a and b). Potassium promotes growth and
counteracts the salt stress induced growth inhibition in different crop species e.g.
strawberry (Kaya et al., 2001a), spinach (Kaya et al., 2001b), cucumber and pepper
(Kaya et al., 2003). Application of potassium increased root and shoot length in water
culture experiments on Triticum aestivum L genotypes (Shirazi et al., 2005).
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Application of potassium in appropriate doses increases nitrogen content in the
soluble amino and in the protein fraction of various plant organs in comparison to the
plants maintained at lower potassium status (Mengel et al., 1974). Application of
potassium and magnesium improved the nitrogen metabolism, resulting in increased
synthesis of amino acids in leaves of Camellia sinensis L. (Ruan et al., 1998).
Potassium fertilizer improved total plant yield in tomato, pepper and egg plant
(Hakerlerler et al., 1997). Added potassium resulted in better growth and yield of wheat
crop (Singh et al., 2000).
Potassium deficient soybean leaves contained higher levels of hexose and
sucrose associated with increased activity of acid invertase (Huber, 1984). Deficiencies
of both P and K could be mitigated by foliar spray of KH2PO4 in salt stressed tomato
(Satti and Al-Yahyai, 1995) and strawberry (Kaya et al., 2001a). Spray of KH2PO4 was
effective in increasing grain yield easily but did not affect the final grain weight in
wheat (Sherchand and Paulsen, 1985 and Batten et al., 1986).
Under potassium deficient conditions accumulation of carbohydrates in the
leaves and roots result (Hermans et al., 2006). Potassium deficiency results in reduced
number of leaves and leaf area in maize, wheat, soybean and cotton (Pettigrew, 2008).
Exposure to salt stress and potassium deficiency simultaneously reduced fresh weight
and dry weight of barley to a greater degree (Degl’Innocenti et al., 2009). Stresses of
salinity and potassium deficiency applied in conjunction reduced the biomass
production to a greater degree than when applied individually (Hafsi et al., 2010).
Potassium stress imposed during vegetative development reduced plant dry matter
production and leaf area in cotton (Gerardeaux et al., 2010). Growth of maize seedlings
subjected to potassium deficiency and salt stress were significantly inhibited.
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Compatible solutes accumulated and plasma membrane permeability, lipid peroxidation
as well as reactive oxygen species in these seedlings were higher compared with the
seedlings subjected to either potassium deficiency or salt stress only (Gong et al., 2011).
Improved potassium status in crops reduces incidence of diseases and pests
(Perrenoud, 1990 and Prabhu et al., 2007). Probably higher potassium concentrations
reduced the competition of pathogens for nutrient resources (Holzmueller et al., 2007).
Application of potassium either before or after planting effectively reduces the
incidence of Fusarium wilt and root rot caused by Fusarium oxysporum (Prabhu et al.,
2007). Variability in the effect of potassium on incidence of diseases and pests is related
to the potassium status of plants or to the quantity and type of K applied or to both
(Perrenoud, 1990 and Amtmann et al., 2008). Role of potassium in protecting against a
number of biotic and abiotic stresses such as drought, salinity, cold and frost and
waterlogging has been discussed by Wang et al (2013).
Supplementation of potassium to plants subjected to salt stress could reduce
ROS formation during photosynthesis and inhibit activation of O2- generating NADPH
oxidase (see Cakmak, 2005). Potassium supplementation can enhance K+/Na+ ratio in
cell thereby improving tolerance of plants. Maintenance of optimal K+/Na+ ratio is
important for plant salt tolerance (Tester and Davenport, 2003). Improvement of K
status may be of great value in imparting tolerance of plants exposed to various
environmental stresses like low temperature, drought and salinity (Cakmak, 2005).
Salinity induced production of ROS results into lipid peroxidation, activation of K+
efflux channels, inducing K+ leakage from plant tissues (Demidchik et al., 2003 and
Cuin and Shabala, 2007). Water stress results into generation of oxygen radicals leading
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to lipid peroxidation and the supplementation of potassium can help overcoming the
damage (Soleimanzadeh et al., 2010).
The enzymatic antioxidant system is one of the productive mechanisms which
includes superoxide dismutase in various cell compartments leading to the catalysis of
two O2- radicals to H2O2 and O2 (Scandalios, 1993). Molecular defence systems have
been evolved in plants to limit ROS formation and promote its removal (Alscher et al.,
2002). SOD can convert O2- into H2O2 and O2, whereas CAT and APX can reduce H2O2
into H2O and O2. Antioxidant enzymes such as the phenol peroxidase (POX), ascorbate
peroxidase (APX), glutathione peroxidase (GPX), superoxide dismutase (SOD) and
catalase (CAT), with other enzymes of the ascorbate glutathione cycle scavenge ROS
(Cavalcanti et al., 2004).
Interest has been increasing considerably in finding naturally occurring
antioxidants for use in foods to substitute for synthetic antioxidants which are being
restricted because of their potential carcinogenicity (Ito et al., 1983). Fenugreek seeds
are widely used as milk producing agent by nursing mothers improving breast milk
supply (Fleiss, 1988). Fenugreek seeds contain lysine and L-tryptophan rich proteins,
mucilaginous fiber and other chemical constituents such as saponins, coumarin,
fenugreekine, nicotinic acid, sapogenins, phytic acid, scopoletin and trigonelline, which
possibly contribute towards antidiabetic and many of its therapeutic effects (Ribes et al.,
1986 and see Bukhari et al., 2008 also). An account of Regional medicinal plants used
by the rural folk as a traditional remedy for common diseases in Iran has been given by
Miraldi et al. (2001). Fenugreek mixed with cotton seed increases milk flow in cows.
Fenugreek mixed with sour hay makes palatable to the cattle. Fenugreek contributes as
an ingredient to produce clarified butter, which is similar to Indian ghee. Fenugreek
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seeds are mixed with yoghurt and used as conditioner for hair in India (Leela and
Shafeekh, 2008).
Flavanoids, a group of polyphenolic compounds are commonly present in fruits,
vegetables, leaves, nuts, seeds, barks, roots and in other plant parts. These substances
have generated considerable interest in the field of food chemistry, pharmacy and
medicine due to a wide range of favorable biological effects because of being
antioxidants, metal chelators, free radical scavengers inhibiting lipid peroxidation
(Cook and Samman, 1996). Food sources having antioxidant nutrients are advantageous
to health (Aruoma, 1998).
Plants are rich sources of polyphenols which are natural antioxidants (Sharma et
al., 2009). Tannins form stable complexes with proteins, starch and metals altering the
nutrient availability, activity of bacterial enzymes and function of biological membranes
thereby exhibiting antimicrobial activity (Bialonska et al., 2009a). Polyphenols derived
from plants are well known for their antioxidant potency (Bialonska et al., 2009 b). A
number of antioxidants scavenging free radicals have been analysed in dietary sources
particularly fruits, vegetables and grains (the plant materials mentioned in Holy Quran)
and a correlation between phenolic content and antioxidant activity has been noticed
(Qusti et al., 2010).
Tannins are a group of polyphenols formed as secondary plant metabolites
occurring in human diet. Condensed tannins from four sources viz., green tea, grape
seed, Mimosa and sorghum have been studied and the data has been discussed with
relation to the structures and the already known nutritional effects of condensed tannins
(Frazier et al., 2010).
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Spices and aromatic herbs in diets or medical therapies delay aging and
biological tissue deterioration and have been used as source of natural antioxidants.
Frankel (1996) have reviewed the antioxidant property of tocopherols and ascorbic acid
in edible oils and influence of interfacial phenomenon on their activities. By virtue of
being electron rich the natural antioxidants polyphenolic compounds such as flavonoids,
flavonols and terpenoids etc. from plant origin can donate electrons to ROS and
neutralize these chemical species and therefore have been used as favored choice
(Halliwell, 1996 and Gil et al., 1999). Leafy and green vegetables are rich in bioactive
molecules such as carotenoids and polyphenols and have health promoting potential
(Moller et al., 2000).
Antioxidants such as carotenoids, vitamins, phenols, flavonoids, dietary
glutathione and many enzymes naturally present in plants are capable of performing a
number of functions which includes free radical scavenging singlet and triplet oxygen
quenching, enzyme inhibition etc (Larson, 1988). Antioxidants such as ascorbate and
carotenoids present in fruits provide protection against free radicals and play preventive
role against various diseases in human being (Ames et al., 1993). Natural products are
preferred over synthetic antioxidants because of being safer in consumption and the
antioxidant properties of the plant materials such as spices have been reported by many
workers and ascribed to many active phytochemicals such as; vitamins, carotenoids,
flavonoids, phenols, terpenoids, phytosterols etc (Madsen and Bertelsen, 1995; Madsen
et al., 1996; Kahkonen et al., 1999; Zheng and Wang, 2001 and Calucci et al., 2003).
Many aromatic, medicinal and spice plants contain compounds possessing confirmed
strong antioxidative components and the medicinal properties of plants have been
investigated in the recent times throughout the world, focusing more on their
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antioxidant activities, side effects and economic viability. Natural antioxidants provide
a side effect free alternative to synthetic antioxidants (Chaurasia et al., 1995 and
Krishnaiah et al., 2011).
Above perusal of literature indicates that there are hardly any reports regarding
potassium induced alterations in the antioxidants both enzymatic and non-enzymatic
components which has prompted us to analyse the antioxidant potential of fenugreek as
affected by potassium application. Following objectives were identified for the present
study:
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In plants polyphenol compounds such as flavonoids and phenolic groups are widely
distributed and have been reported to scavenge free radical and show anti-inflammatory
and anti tumour activity etc (Irshad and Chaudhuri, 2002 and Huang et al., 2005) and
not many reports are available on the influence of application of potassium on these
components. Therefore, analysis of total phenols, tannins and free amino acids with and
without potassium treatments was undertaken.
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Assay of the enzymes particularly the ones involved in antioxidant and free radical
scavenging activities such as super oxide dismutase (SOD), catalase (CAT) and
guaiacol peroxidase has been carried out.
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Evaluation of the impact of potassium on overall growth of fenugreek has also been
undertaken.