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~~~ PLANT DEFENSE SYSTEMS ~~~
Many plants are known to contain polyphenols (a.k.a. tannins)
of which thousands have been identified.
Upon exposure to oxyradicals, polyphenols can readily donate
hydrogen atoms and thereby serve as "antioxidants"
for the plants or the animals which eat them.
Upon physical injury to plant cells, prooxidant enzymes
These enzymes are usually the copper containing laccases,
or the ferroporphyrin containing peroxidases.
These enzymes oxidize the polyphenols to produce orthoquinones.
Orthoquinones are themselves oxidants and have demonstrable
Orthoquinones also react with primary amines to produce imines.
Imines in turn may polymerize, which process has an astringent
effect preserving cellular fluid much like a clotting system.
The process of imine and polymer formation is associated
with a brown or tan color, hence the name tannins.
---C---OH laccase ---C===O
|| + [O] ---------> |
---C---OH peroxidase ---C===O
---C===O H ---C===N---R
| + N---R ---> | + H2O
---C===O H ---C===O
ESTERS OF GALLIC ACID: HO--C--CH O
// \\ //
\ / \
Source: Haematoxylon campechianum a.k.a."logwood"
The ether extract is oxidized to hematein, which is
orange in color and useful as an histologic stain.
Traditionally used as astringent & antidiarrheal.
CH2 OH CH
/ \ / // \
O C--CH2--C C--OH
| | | ||
C CH------C C--OH
/ \\/ \\ /
HO--C CH CH
NOR-DIHYDROGUAIARETIC ACID (NDGA):
Source: Larrea divaricata or mexicana,"creosote bush"
Used as antibacterial and antitumor agent.
|| \\ // ||
HO--C CH HC C--OH
\ | | /
HC==C CH3 CH3 C==CH
\ | | /
H H H H