suggested that molecular mechanisms were activated during development to deal
with heavy metal stress, with potential stress tolerance genes identified (Ahmad
et al. 2015 ). THC content was only slightly effected by heavy metals, although this
may be due to the naturally low THC, hemp variety used in the studies. However,
the majority of work performed observed the uptake of heavy metals into plant
tissues, a problem if the plants are to be used pharmaceutically. One potential
solution is the use of mycorrhizal fungus, which have been documented to affect the
translocation of heavy metals within the plant (Citterio et al. 2005 ). Either way, the
issue of accumulation must be addressed before they can be considered appropriate
as potential elicitors.
21.8 Wounding
Wounding, more specifically caused by insect herbivory, may affect cannabinoid
content in cannabis. This is logical based on the evidence for cannabinoids’role as
an insecticide or insect deterrent. Cannabis rich in THC was toxic to tiger moth
larvae (Rothschild et al. 1977 ) and a leaf extract of cannabis caused paralysis in
Chironomous samoensislarvae (Roy and Dutta 2003 ). Pure THC deterred but-
terflies from laying eggs on cabbage leaves (Rothschild and Fairbairn 1980 ). It is
also plausible that cannabinoids may act as a physical barrier to feeding insects
which can rupture the glandular trichomes in which they are stored (Ledbetter and
Krikorian 1975 ). In addition to cannabinoids, cannabis produce a large variety of
terpenes, some of which are known to possess insecticidal activity (Mithofer and
Boland 2012 ). While elicitation of terpene synthesis by insect feeding has been
documented in a number of plants, no work has been published on cannabis. While
mimicking insect wounding is a potentially promising tool, much more work is
needed to better elucidate its ability to modulate cannabinoid biosynthesis.
21.9 Pathogens
Both bacterial and fungal pathogens have been implicated as factors which may
modulate cannabinoid biosynthesis in cannabis. Thefirst support for this is the
possible anti-microbial activity attributed to cannabinoids. As early as 1952, can-
nabis extracts have been documented to possess antibacterial activity (Krejci 1952 ;
Ferenczy et al. 1958 ; Radosevic et al. 1962 ; Turner et al. 1980 ). Subsequently,
individual cannabinoids were analyzed, revealing that a number of cannabinoids are
potent antibiotics (Gal and Vajda 1970 ; Farkas and Andrassy 1976 ; Van Klingeren
and Ten Ham 1976 ; ElSohley et al. 1982 ), and even against antibiotic resistant
strains (Appendino et al. 2008 ). Interestingly, this activity, described against
446 J. Gorelick and N. Bernstein