Agriculture Reference
In-Depth Information
On the basis of their origin, structure and type, elicitors can be classified as biotic
and abiotic (Eilert
1987
; Barz et al.
1988
). There is one more benefit of the use
of elicitors is that they also encourage release of the metabolites into the medium
(Pitta-Alvarez et al.
2000
).
BioticElicitors
These are chemically complex biological compounds with unknown composition
like microbial cell-wall preparations and yeast extract. In some cases, and particu-
larly in recent years, elicitors with known chemical structure have been selected
which helped in more detailed investigation of the elicitation process. Carbohy-
drates and proteins are examples of such defined elicitors (Radman et al.
2003
).
Different workers further classified these substances on the basis of their similarity.
Material from living organisms include different polysaccharides from plant cell
walls (pectin or cellulose) and microbial extracts (chitin or glucans) and glycopro-
teins (Eilert
1987
; Nishi
1994
; Benhamou
1996
; Shirsau et al.
1997
); phytoalexins:
which are low-molecular-mass antimicrobial secondary compounds synthesized by
plants in reaction of fungal or bacterial attack and physical damage. Protein kinase:
regulate growth and cellular development by phosphorylating a number of target
proteins;
calmodulin
: intracellular Ca
2
+
-binding proteins consisting of at least two
different peptides, with four Ca
2
+
binding sites;
calmodulin
has no enzyme activity
of its own, but acts by binding to other proteins (Radman et al
2003
, Angelova et al.
2006
). Recently Siddiqui et al. (
2010
) described fungal elicitor as a potent approach
for enhancing secondary metabolites in cultured cells.
AbioticElicitors
As compared to biotic elicitors the use of abiotic elicitors in plant cell cultures
has received less interest (Radman et al
2003
, Angelova et al.
2006
). Abiotic elici-
tor or stress agents are non-biological substances which includes different kinds of
inorganic salts and physical factors like UV radiation, heavy metal salts (Cu and
Cd ions), Ca
2
+
, high pH and other chemical compounds with diverse mechanism of
action (Eilert
1987
; Radman et al
2003
). Recently Zuccarini (
2009
) reviewed ozone
as a fungal elicitor. Addition of AgNO
3
and CdCl
2
to the cultures of
Brugmansia
candida
(angel's trumpet) enhanced significantly the accumulation and release of
these alkaloids, but CdCl
2
inhibited the growth of the hairy roots (Pitta-Alvarez
et al.
2000
). Wu et al. (
2001
) investigated the synthesis of taxol in cell cultures
of
Taxus
sp. under the influence of the rare-earth metal lanthanum and reported
a considerable augmentation (280 %) of taxol. Although elicitation has been car-
ried out in large number of medicinal plants but for this chapter we extensively
studied it in
C. roseus
. There is a great importance of this plant as it is an important
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