Molecular Plant Breeding 2015, Vol.6, No.14, 1
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metals (Singh et al., 2010). It is quite in agreement
that plant’s responses to heavy metal stress very often
undergo interacted by some chemical elicitors either
endogenous or exogenous in application (Hossain et
al., 2012). The elicitors have been played to modulate
the metal absorption in a number of ways including
adsorption of the ion on the cell wall (facilitated
diffusion of the ions over the membrane, moderation
of metal induction for ROS development and finally
transduce the signal into nucleus for gene expression.
The later is manifested in amelioration of the metal
induced damages (Gill and Tuteja 2010). However, the
actual insight for the role of apoplast in metal
transport and its immobilization within the tissues are
less studied, particularly, in lower groups of plants.
Admitted well that cell wall matrix and its projected
chemical moieties have been intrinsic affinity for
adsorption of different metallic ions. This very often
undergoes some deviations with metal hindrance with
reference to bending and stretching of bonds furnished
byfunctional groups (Vasconcelos et al., 2014). Those
include complex polysaccharides, proteins, lipid with
glycerophosphate residues etc. It is also reported that
those chemicals are often shown to be easily
biodegradable, forming chemical conjugants with the
metals on the cell wall or even within the apoplastic
spaces (Nguema-Ona et al., 2014). Thus, hyper-accu-
mulating plant species are escaped from the vulnerability
of metal toxicity through inhibition of downstream
paths into cytosol crossing the cell membrane by
sorption of metals.
Amongst the elicitors found in plant system, polyamines
have been implicated the most authentic one with
regards to their nature and functionales. These cover
their ubiquitous existence in tissues, low molecular
weight, high solubility and diffusivity, non-hindering
the cellular pH as well as with a wider span of
physiological activities (Minocha et al., 2014).
Polyamines have been encountered in a diverse mode
of action for various abiotic stresses including metal
toxicity, mostly in higher plants. Lower groups of
plants representing the pteridophytic species have also
been evaluated for polyamine sensitivity with special
reference to metal stress also (Mandal et al., 2013).
According to the molecular configuration of polyamines,
the lower molecular weight moieties are most
effectively used for their rapid diffusivity over the
membrane as well as dose-dependent activity. Thus,
putrescine (diamine), spermidine (triamine) and
spermine (tetraamine) are very often used in plant
responses to abiotic stresses (Hossain et al., 2012).
Therefore, it could be an assumption that polyamines
may have some influences in effects on the
biosorption phenomenon of metals in plant species.
Wide arrays of information have enriched the
effectiveness of polyamines for biosorption of metal in
angiospermic plants. However, for non-angiospermic
plants the responses to polyamines are rather scares
and essentially needs to explore its fate of application
for metal remediation in soil. Despite this, some
aquatic pteridophytes like
Salvinia
,
Azolla
which
represents their tolerance to some specific heavy
metals has set examples with reference to polyamine
sensitivity (Mandal et al., 2013). Therefore, we
hypothesize that some specific features enabling the
metal resistance in fern species might be through
adsorption phenomenon by polyamine moieties also.
Thus, the present experiment is based on the
evaluation of
Marsilea
plant selecting Cd as a heavy
metal with interaction of spermidine for hyper-accum-
ulation property. The changes of specific cell wall
constituents with the interference of Cd toxicity in this
species have been described in some details.
Result and Discussion
From the facts and figures of the present experiment
with
Marsilea
plant incubated under different Cd
concentrations, it recorded that plants were significantly
affected with Cd bio-adsorption and accumulation. In
our earlier studies, the bio-accumulation of Cd was
found in parallel with concomitant concentrations of
metal supplied
et al., 2013). In addition to
this, it had also documented with a significant changes
of cell surfaces with some irregular patches under Cd
induction (Das et al., 2014). In the present experiment,
a detailed analysis and its possible interpretation was
attempted with EDAX studies in
Marsilea
plants for
Cd bio- adsorption (Figure 1a-1e). Removal of metals
by biological remediation is essentially based on
bio-adsorption followed by accumulation. The mechanism
of this process involves precipitation of the metals in
extracellular spaces and on cell surfaces (Gaur et al.,
2014). This also may be hypothecated that cell
surfaces might be furnishing with some functional
groups projected from biomolecules of cell wall to
anchor the adhering metals (Simon AA, García-Angulo P,
Melida H, Encina A, Alvarez JM, Acebes JL 2011).
