123
8
Used in Europe at least since the 1900s, the use in Persia dates back much longer (McLaughlin
1973). The action of pyrethrins on voltage-gated Na + -channels is well described; however, an
additional action against voltage-gated Ca 2+ and Cl – channels has also been suggested
(Soderlund et al. 2002). Pyrethrins have a high arthropod toxicity (also for fish) but much
lower toxicity to mammals and birds (Soderlun and Lee 2001; Vais et al. 2000; Mauck and
Olson 1976) indicating that they are used as feeding deterrent against arthropod herbivores.
However, antifungal and antibacterial activity was also reported (Ramirez et al. 2013). The
pyrethrin precursor chrysanthemic acid is synthesized in the apical cell of glandular trichomes that cover the flower achenes even though only sesquiterpene lactones are found in
the trichomes of mature achenes. Instead, chrysanthemic acid is transported to the pericarp
of the fruit, where, after esterification to pyrethrin, it accumulates outside the cells within the
intercellular space. From there, the pyrethrins are taken up by the embryo, where they are
believed to protect the seedling against insects and fungi (Ramirez et al. 2012).
Voltage-gated Na + -channels are also the target of the guanidium toxin saxitoxin and its
analogues alkaloids neosaxitoxin and gonyautoxin (Cembella 1998). Well known as paralytic shellfish toxins, they are not classical plant-derived secondary metabolites. However,
they are also not produced by the shellfish but can accumulate in these organisms via
feeding on marine dinoflagellates such as Alexandrium catenella, A. tamarense excavatum
or Pyrodinium bahamense. It is also produced by a number of freshwater cyanobacteria
(Kellmann et al. 2008; Wiese et al. 2010).
By contrast, the polycyclic diterpene ryanodine is the name-giving compound that
reacts with the ryanodine receptors, a group of Ca 2+ -induced Ca 2+ -release channels in
muscle tissue. It is found in Ryania speciosa, a South American species from the
Salicaceae (Rogers et al. 1948). It affects the channel by locking it either in the half-open
or closed state depending on its concentration (Thomas and Williams 2012). Historically,
extracts from Ryania plants have been used in South and Central America as arrowhead
poisons (Santulli and Marks 2015). It was also used as a pesticide and insecticide, the
latter indicating that fending of insect larva might be the functional role of this toxin for
the plant.
8.2 Nicotinic Acetylcholine Receptors: Nicotine, Coniine, Curare
and Anatoxin A
As described in 7 Chap. 2, a nicotinic agonist is a drug that mimics the action of acetylcholine at nicotinic acetylcholine receptors (. Fig. 8.2). Plants contain a number of nicotinic agonist, foremost the name-giving pyridine alkaloid nicotine that is found in several
plants of the Solanaceae but is best known as the main alkaloid from tobacco. The Nicotiana
genus consist of a number of species (. Fig. 8.3) found in the Americas, Australia, SouthWest Africa and the South Pacific, which occur both as herbaceous plants as well as scrubs,
and many of which are poisonous to livestock and humans. N. tabacum is a perennial
herbaceous plant that is found exclusively in cultivation. It originated in the highland of
the Andes, probably Bolivia or northern Argentina, and is believed to be a hybrid of two
older species, N. sylvestris and N. tomentosiformis (Murad et al. 2002).
Nicotine is toxic to mammals in high doses and it has even been used as poison (see
7 Box 8.1). In insects, small doses result in reduced activity and paralysis (Kennedy and
Wightman 2011; Wolf and Heberlein 2003), and therefore, extracts of tobacco leaves
were a popular pest control method up to the beginning of the twentieth century. While
8.2 · Nicotinic Acetylcholine Receptors: Nicotine, Coniine, Curare and Anatoxin A
8
Used in Europe at least since the 1900s, the use in Persia dates back much longer (McLaughlin
1973). The action of pyrethrins on voltage-gated Na + -channels is well described; however, an
additional action against voltage-gated Ca 2+ and Cl – channels has also been suggested
(Soderlund et al. 2002). Pyrethrins have a high arthropod toxicity (also for fish) but much
lower toxicity to mammals and birds (Soderlun and Lee 2001; Vais et al. 2000; Mauck and
Olson 1976) indicating that they are used as feeding deterrent against arthropod herbivores.
However, antifungal and antibacterial activity was also reported (Ramirez et al. 2013). The
pyrethrin precursor chrysanthemic acid is synthesized in the apical cell of glandular trichomes that cover the flower achenes even though only sesquiterpene lactones are found in
the trichomes of mature achenes. Instead, chrysanthemic acid is transported to the pericarp
of the fruit, where, after esterification to pyrethrin, it accumulates outside the cells within the
intercellular space. From there, the pyrethrins are taken up by the embryo, where they are
believed to protect the seedling against insects and fungi (Ramirez et al. 2012).
Voltage-gated Na + -channels are also the target of the guanidium toxin saxitoxin and its
analogues alkaloids neosaxitoxin and gonyautoxin (Cembella 1998). Well known as paralytic shellfish toxins, they are not classical plant-derived secondary metabolites. However,
they are also not produced by the shellfish but can accumulate in these organisms via
feeding on marine dinoflagellates such as Alexandrium catenella, A. tamarense excavatum
or Pyrodinium bahamense. It is also produced by a number of freshwater cyanobacteria
(Kellmann et al. 2008; Wiese et al. 2010).
By contrast, the polycyclic diterpene ryanodine is the name-giving compound that
reacts with the ryanodine receptors, a group of Ca 2+ -induced Ca 2+ -release channels in
muscle tissue. It is found in Ryania speciosa, a South American species from the
Salicaceae (Rogers et al. 1948). It affects the channel by locking it either in the half-open
or closed state depending on its concentration (Thomas and Williams 2012). Historically,
extracts from Ryania plants have been used in South and Central America as arrowhead
poisons (Santulli and Marks 2015). It was also used as a pesticide and insecticide, the
latter indicating that fending of insect larva might be the functional role of this toxin for
the plant.
8.2 Nicotinic Acetylcholine Receptors: Nicotine, Coniine, Curare
and Anatoxin A
As described in 7 Chap. 2, a nicotinic agonist is a drug that mimics the action of acetylcholine at nicotinic acetylcholine receptors (. Fig. 8.2). Plants contain a number of nicotinic agonist, foremost the name-giving pyridine alkaloid nicotine that is found in several
plants of the Solanaceae but is best known as the main alkaloid from tobacco. The Nicotiana
genus consist of a number of species (. Fig. 8.3) found in the Americas, Australia, SouthWest Africa and the South Pacific, which occur both as herbaceous plants as well as scrubs,
and many of which are poisonous to livestock and humans. N. tabacum is a perennial
herbaceous plant that is found exclusively in cultivation. It originated in the highland of
the Andes, probably Bolivia or northern Argentina, and is believed to be a hybrid of two
older species, N. sylvestris and N. tomentosiformis (Murad et al. 2002).
Nicotine is toxic to mammals in high doses and it has even been used as poison (see
7 Box 8.1). In insects, small doses result in reduced activity and paralysis (Kennedy and
Wightman 2011; Wolf and Heberlein 2003), and therefore, extracts of tobacco leaves
were a popular pest control method up to the beginning of the twentieth century. While
8.2 · Nicotinic Acetylcholine Receptors: Nicotine, Coniine, Curare and Anatoxin A