limitless, there are a few major obstacles which hinder large scale utilization by the
modern western medical system. Among these is the lack of reproducibility com-
mon in testing many plant extracts (up to 40%), which has limited the enthusiasm in
developing plant based pharmaceuticals. Unlike standardized single entity phar-
maceutical drugs, herbal medicines consist of complex mixtures with multiple
compounds responsible for therapeutic activity, making standardization difficult
(Schmidt et al. 2007 ). Further complicating the issue is the fact that plants, unlike
synthetic medicines, are living organisms, with inherent biological variation (Shaw
et al. 2012 ). Just because plant material originates from the same species does not
necessarily mean that the chemical content is identical. This lack of reproducibility
may be due to two main factors, genetic variability and differences of growing
conditions.
Genetic variation between plants is a major source of variation in plant sec-
ondary metabolites, seriously affecting the amounts and type of metabolites pro-
duced and hindering reproducibility in testing (Poulev et al. 2003 ). This is certainly
the case with cannabis, where there can be large quantitative as well as qualitative
differences in the composition of bioactive secondary metabolites between different
varieties. This variation can be partially eliminated through the generation of uni-
form plant material by the use of vegetative propagation of selected plants, as
opposed to harvesting wild plants, to insure consistent levels of secondary
metabolites (Bernath 2002 ).
Environmental condition is the other major factor which contributes to variation
in chemical composition of plant material. Light, temperature, relative humidity,
water availability, and salinity were all demonstrated to affect plants’secondary
metabolites (Nascimento et al. 2010 ). Many bioactive compounds such as cyano-
genic glycosides and glucosinolates are produced by plants to combat water stress
(Waterman et al. 1989 ). Nutrient deficient conditions may lead to greater synthesis
of the non-nitrogenous shikimic acid derived metabolites (Fluck 1963 ). Increased
light intensity may lead to higher levels of terpenoids and phenolic compounds
(Downum et al. 1991 ). Biological factors such as bacterial, fungal, and viral
pathogens as well as insect damage and herbivory also contribute to plant secondary
metabolism (Berenbaum 1995 ). However, relatively little work has been performed
regarding environmental effects on cannabis secondary metabolites.
21.2 Stress Response
One major reason why these factors alter plant chemical composition is the stress
response. As mentioned above, stress may be the result of biotic or abiotic sources.
Biotic sources of stress are caused by living organisms, such as a fungal pathogen
or a feeding insect. Compounds produced by living organisms, such as fungal wall
derivatives or signaling molecules can also be sources of biotic stress. Abiotic stress
arises from non-biological stresses, such as mineral deficiency, shortage of water or
salinity. When a plant is exposed to stressors, also called elicitors, enzymatic
440 J. Gorelick and N. Bernstein