In vitro Production of Secondary Metabolites Using Elicitor in Catharanthus roseus: A Case Study - Crop Improvement: New Approaches and Modern Techniques - page 408

investigation. It is further reported that this sequence of events is not followed by
all elicitors, in some peptide elicitors plasma-membrane receptors are active (Ne-
nnstiel et al. 1998 ), certain peptides of bacterial origin act themselves as messenger
of invasion signals and get transported to distal tissues. The systemic necrosis due
to these proteins is not stimulated by rapid secondary signaling, but by transporta-
tion of the elicitor inside the tissue (Devergne et al. 1992 ). On the basis of available
information, we summarize the following role/involvement of elicitor in the course
of essential events in secondary metabolism.
• Binding of the elicitor to plasma membrane receptor.
• Changes in Ca 2 + influx to the cytoplasm from extracellular and intracellular
pools.
• Decrease of pH of the cytoplasm and activation of NADPH oxidases, protein
phosphorylation patterns and protein kinase activation.
• Changes in cell wall structure (lignification) and in generating reactive oxygen
species.
• Synthesis of JA and SA as secondary messengers.
• Activation of genes that produce defence-related proteins, plant defence mol-
ecules like phytoalexins and other secondary compounds including alkaloids.
In the same way elicitor-based signaling model has been proposed recently for en-
hanced activation of gene expression in C. roseus (Fig. 14.1 ) where alkalization
of the medium by influxing proton molecule (particularly by calcium) was carried
out by yeast elicitor. This in turn stimulates the octadecanoid pathway and synthe-
sis o JA takes place. JA act as secondary messenger and influences the synthesis
of nuclear proteins ORCA2 and ORCA3. These proteins interact with TDC- and
'JA-responsive STR' promoter of several biosynthetic genes and activate their gene
expression (Memelink et al. 2001 ). Due to 'elicitor-receptor' mediated signaling, a
large number of key gene's activities such as Tdc , Str , geraniol 10 dehydrogenase
( Gh ), anthranilate synthetase ( As ) increased (Van der Fits and Memelink 2000 ). We
also believe that this architecture will evolve in future as refinement of cell biology
and molecular biology approaches will allow further and full dissection of plant cell
signaling pathways that effectively regulate elicitation events in C. roseus .
Conclusion and Future Perspectives
C. roseus is a very important plant due to large number of alkaloids which are used
in treatment of various diseases including antineoplastic agents VLB and VCR.
Present review provides an overview of external stress stimuli used for eliciting C.
roseus cell to undergo a complex network of reactions which ultimately lead to the
synthesis and accumulation of secondary metabolites. These secondary metabolites
help out the plant to endure in stress challenge. They are also under high demands
due to their pharmacological activities but due to the poor understanding of plant