(Buchanan et al. 2000 ). More than 100,000 secondary metabolites are known
until date.
The amount of any plant secondary compound found in an organism is the result
of an equilibrium among synthesis, storage, and degradation. Regulation of sec-
ondary metabolism is complex. The onset of secondary metabolism is linked to the
developmental stage of the organism and is often closely linked to morphological
and cytological changes (Haslam 1986 ). In general, the formation of products
during secondary metabolism appears to be enzyme limited, but the level of sub-
strates present influences the production of secondary metabolites, especially in
artificial culture. The degree to which one prevails often depends on the develop-
mental stage of the plant and a variety of other factors.
Plant secondary metabolites vary in complex ways, not only because of genetic
differences but also in response to environmental factors. Both qualitative and
quantitative variation of secondary metabolites is known to occur in response to
various types of stress. Among these are biological stresses such as attack by fungi,
bacteria, nematodes, insects, or by grazing by mammals, and abiotic stress such as
extremes of temperature and moisture, shading, presence of heavy metals, and
injury.
Individuals from natural populations of plants often differ in the amounts and
types of compound present. Roots, leaves, stems, seeds, fruit walls,flowers, and
buds frequently differ in chemical composition. Further, each of these parts may
vary at different stages of development and at various times of the year. Daily
variation of many compounds also occurs (Seigler 1998 ).
Study of the biochemistry of plant natural products has many practical appli-
cations. Biotechnological approaches can selectively increase the amounts of
defense compounds in crop plants, thereby reducing the need for costly and
potentially toxic pesticides. Similarly, genetic engineering can be utilized to
increase the yields of pharmaceuticals,flavor and perfumery materials, insecticides,
fungicides, and other natural products of commercial value (Buchanan et al. 2000 ).
Polyploidy is another way to increase plant secondary metabolites. Polyploidy
can induce metabolite biosynthesis because of an increasing level of related genum
or gene expression under special condition.
17.1.2 Polyploidy
Polyploidy has provided an important pathway for evolution and speciation in
plants. A polyploid is simply an organism that contains more than two complete
sets of chromosomes. This process is found rarely in animals. In plants however,
polyploidy occurs naturally and is very common.
The term“ploidy”or“ploidy level”refers to the number of complete sets of
chromosomes and is notated by an“x.”An individual with two sets of chromo-
somes is referred to as a diploid (2x), three sets would be a triploid (3x), tetraploid
(4x), pentaploid (5x), hexaploid (6x), etc. (Ranney 2006 ). Polyploids were created
17 Induction of Polyploidy and Its Effect onCannabis sativaL. 367