Diesel Trees - Bioenergy Crop Plants - page 621

diterpenes are thought to be derived primarily from isoprenes made in the plastid through the MEP
pathway, whereas sesquiterpenes are derived from isoprenes made in the cytosol where the MVA
pathway occurs. Movement of intermediates between these two pathways has been demonstrated in
plants (Cheng et al. 2007).
The chemical compounds present in Copaifera oleoresin vary not only with tissue type (Gramosa
and Silveira 2005; Chen et al. 2009) but also seasonally (Cascon and Gilbert 2000; Zoghbi
et al. 2007), and among species (Veiga Junior et al. 2007). Therefore, any future genomics-based
characterization of Copaifera trees must be coupled with close biochemical analysis to correctly
match major compounds present in each tissue at the time of sampling. Identification of particular
chemicals responsible for the pharmaceutical effects of Copaifera oleoresins will be necessary in
the future because high chemical variability within samples, seasons, and species will inherently
affect the effectiveness, dosage, and safety for patients.
24.3 BIosynthesIs oF copAiferA oleoresIns:
What conIFers can teach us
Not much is known about the biosynthesis of Copaifera oleoresins because most studies have been
focused on traditional ecology and forestry of the genus. However, conifer resins have been thoroughly
studied for over 40 years. These oleoresins are essentially made of the same basic constituents as
Copaifera oleoresin: mono-, di-, and sesquiterpenes. Conifer oleoresins usually have an equal part of
mono- and diterpene compounds with lower concentrations of sesquiterpenes (Martin et al. 2002).
Monoterpenes are volatile components found in oleoresins. Monoterpene synthases have been
extracted from the woody stems of ten conifer species, and their activities have been measured
(Lewinsohn et al. 1991). Species with resin ducts showed the highest levels of monoterpene
cyclase activity from wood extracts, suggesting that monoterpene synthesis for oleoresins
occurs in epithethial cells surrounding the resin ducts. Diterpenoids themselves are not typically
found in conifer oleoresins in large quantities. Instead, modifications such as hydroxylation and
oxidation occur, so the alcohol, aldehyde, and predominantly acid products are present (Keeling
and Bohlmann 2006). These modified diterpene products harden the resin and form rosin after
the volatile constituents evaporate. Sesquiterpenes, like monoterpenes, are volatile and are major
constituents of Copaifera oleoresin. The three major chemical constituents, based on percentage
of oleoresin from different species, are presented in Table 24.1. Although the percentages vary,
β-caryophyllene is the major sesquiterpene product of oleoresins throughout Copaifera species that
have been studied to date. Other than these major three sesquiterpenes in each species, there is a
great diversity of terpenoids produced in the oleoresin. Nuclear magnetic resonance (NMR) studies
have found previously undescribed diterpenes (Monti et al. 1996, 1999) that seem to be unique in
biolog y.
Conifers produce a myriad of specialized tissues to store and secrete oleoresins that range from
simple resin blisters to intricate networks of resin ducts (Martin et al. 2002). Copaifera trees form resin
ducts throughout their xylem tissue that can easily be seen in cross-sections (Calvin 1980). Copaifera ,
Hymenaea , and Daniella resin ducts display many structural similarities (Langenheim 2003).
Conifer oleoresins accumulate in resin ducts throughout their lifetimes, but a local response can
also be induced during mechanical damage, herbivory, or even fungal inoculation. This response
activates epithelial cells in resin ducts, signals for formation of special traumatic resin ducts in stem
xylem tissue, and induces diterpene biosynthesis gene transcripts (Keeling and Bohlmann 2006).
Methyl jasmonate can also induce this response (Martin et al. 2002). Oleoresin production can also
be induced in Copaifera species. Younger trees that do not produce oleoresin on the first attempt
have been known to produce a small amount on a second tapping, putatively through induction by
mechanical damage (Plowden 2003; Medeiros and Vieira 2008). Medeiros and Vieira (2008) were
also able to draw a weak correlation between trees with termite infestations and production of
oleoresin, suggesting that insect damage can induce production of oleoresins.