concentration of other cannabinoids tested including CBD, CBG, and CBC. In
addition, UVB did not produce any physiological or morphological change in the
plants. In another study, cannabis leaves were exposed to UV-C radiation and
analyzed for changes in secondary metabolite biosynthesis (Marti et al. 2014 ).
While no significant change was observed in cannabinoid content, significant
increases in stilbenes and cinnamic acid amide derivatives. While these compounds
are known to possess bioactivity, their therapeutic role in cannabis remains to be
determined. In addition, the relevance of thesefindings, which were performed on
detached leaves, to applications on whole plants is difficult to ascertain. As many
interrelated factors are involved including drought and heat stress, it is difficult to
ascertain the specific role of UV radiation in cannabinoid biosynthesis.
21.7 Heavy Metals
Exposure to high metal concentrations affects growth and development of plants
(Rout and Das 2003 ; Shanker et al. 2005 ). The growth effects result from changes
in physiological factors such as photosynthesis, respiration, enzyme activity, lipid
composition, and nutrients distribution in the plant (Sheoran et al. 1990 ; Van
Assche and Clijsters 1990 ; Rout and Das 2003 ; Shanker et al. 2005 ). Although
much information is available concerning the effects of heavy metals on plant
growth and physiology, much less is known about effects on production of sec-
ondary metabolites. Heavy metal-induced changes in metabolic activity of plants
can affect production of photosynthetic pigments, sugars, proteins, and non-protein
thiols. These effects can result from inhibition of enzymes involved in the pro-
duction of these natural products, likely through impaired substrate utilization
(reviewed by Nasim and Dhir 2010 ).
Metals may alter the production of bioactive compounds by changing aspects of
secondary metabolism (Verpoorte et al. 2002 ). Metals including Ni, Ag, Fe, and Co
have been shown to elicit the production of secondary metabolites in a variety of
plants (Zhao et al. 2001 ). Both AgNO 3 and CdCl 2 induced the production of
scopolamine inBrugmansia candida(Pitta-Alvarez et al. 2000 ); lanthanum dra-
matically increased taxol production in Taxus sp. Cultures (Wu et al. 2001 ); and
CuCl 2 (as well as infection by fungal pathogens) increased the content of umbel-
liferone in the leaves of mature tetraploid plants ofMatricaria chamomillaculti-
vated underfield conditions (Repčák et al. 2001 ). Leaf spraying with aqueous
CuCl 2 solutions tripled the content of herniarin, with a simultaneous decline of its
precursors (Z)- and (E)-2-b-d-glucopyranosyloxy- 4-methoxycinnamic acid, and
increased the amount of umbelliferone in a tetraploid and diploid cultivar by 9 and
20 times respectively (Eliasova et al. 2004 ).
There is some work documented the effect of heavy metals in cannabis.
Cannabis was shown to tolerate moderate concentrations of Cd, with no major
effect on plant growth or physiology (Linger et al. 2005 ). Cannabis plants have also
been documented to be tolerant to Ni and Cr (Citterio et al. 2005 ). In fact, it was
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