21.11 Future Role of Elicitation in Development
of Cannabis
Although some work has been done related to elicitation in cannabis, it is still too
soon to be utilized on a large scale. Among the many factors which must be taken
into consideration is the concentration of the elicitor used to treat the plants.
A recurring observation using elicitation is a decrease in secondary metabolite
content with increasing elicitor concentrations (Kuzel et al. 2009 ; Nef-Campa et al.
1994 ; Rijhwani and Shanks 1998 ; Yin et al. 2012 ). This phenomenon may be due
to the induction of the hypersensitive response and resulting cell death. Duration of
the elicitation treatment is another important factor that must be dealt with. In cell
culture, many studies have shown that there is an optimal duration, usually between
24 and 48 h, although this depends on the specific system. Longer treatments with
elicitors can lead to a reduction in secondary metabolite production (Moreno et al.
1993 ; Negrel and Javelle 1995 ). However, it is difficult to extrapolate from cell
culture studies the effect of duration on secondary metabolite production in whole
plants. Numerous factors such asin-plantasignal transport; shoot-root feedback
mechanisms; plant organ developmental-stage specificity in the response to the
elicitors may be specific to the response of whole plants.
Another factor that must be taken into consideration is that elicitor-induced
modulation of the desired biosynthetic pathways can also affect other pathways
with potentially undesirable results. A fungal elicitor can increase the anti-microbial
sesquiterpene content but subsequently reduce the sterol content by activating the
sesquiterpene cyclase genes and suppressing the squalene genes (Chappell 1995 ).
Fungal elicitation can increase the production of 3-deoxyanthocyanidin, but
decrease anthocyanin production (Clive Lo and Nicholson 1998 ). A more thorough
understanding of biosynthetic pathways and more specifically the crosstalk between
different secondary metabolite pathways is vital for effectively eliciting the desired
compounds. To complicate matters, although many elicitors produce similar
responses among a wide range of plants, there are some elicitors that are unique to
specific plant species (Schmelz et al. 2009 ).
Because of the previously mentioned complexity of the plant response to elic-
itation, care must be taken to determine the ideal conditions for any given system.
This is far from a trivial matter as different stressors may have an interactive effect.
In some cases, multiple elicitors can act synergistically. Methyl jasmonate in
combination with oligosaccharides can greatly increase the paclitaxel content of
Taxus canadensis(Linden and Phisalaphong 2000 ). However, in many cases,
multiple elicitors may produce undesirable results. Multiple treatments may
antagonize each other, especially the combination of biotic and abiotic elicitors.
While UV-B elicits the production offlavonoids, when used in conjunction with the
bacterial elicitor,flg22,flavonoid synthesis is suppressed in favor of the production
of anti-microbial phytoalexins (Schenke et al. 2011 ). This phenomenon is at least
partially due to the antagonist relationship between different stress related signaling
pathways such as ABA and SA (Jiang et al. 2010 ). With all of the interactions
21 Chemical and Physical Elicitation... 449