Important specialized metabolites

Compound	Type	Role	Notes	References
Linalool	Monoterpenoid	Floral scent	Monoterpenoid alcohol. Initial breakthrough from (S)-linalool synthase purified from flowers of Clarkia breweri. The expression of (S)-linalool synthase is closely correlated with the synthesis of (S)-linalool in C. breweri.	Pichersky and Gershenzon, 2002
Methyl eugenol, Methyl isoeugenol, Benzyl acetate, Methyl salicylate	Phenylpropanoid	Floral scent	Clarkia breweri	Pichersky and Gershenzon, 2002
Methyl benzoate	Phenylpropanoid	Floral scent	In common garden snapdragon, Antirrhinum majus. A gene encoding the enzyme benzoic acid carboxyl methyl transferase (BAMT), which produces one of the principal floral volatiles of this species, methyl benzoate, was isolated and shown to be flower-specific. The expression of BAMT, which belongs to the same family as salicylic acid carboxyl methyl transferase (SAMT), is tightly correlated with the synthesis of methyl benzoate. The gene encoding BAMT is expressed exclusively in epidermal cells of the petals, some of which have a conical shape that increases their surface area [15••]. Interestingly, there is a higher concentration of the enzyme in parts of the petal that are closer to the path that bees take to reach the nectar, including the ‘hairs’ (i.e. unicellular glands) found in the center of the basal petal. Hence, the scent may serve as guide for bees to find their way inside the flower.	Pichersky and Gershenzon, 2002
Isoprene	Monoterpenoid	Photoprotection, signaling	C5 terpene released from foliage of many species. Isoprene may act by physically stabilizing the thylakoid membranes at high temperatures or by quenching reactive oxygen species, such as ozone, which can lead to membrane damage. Produced by isoprene synthase from dimethylallyl phosphate.	Pichersky and Gershenzon, 2002
S-methyl-methioinine	Amino acid derivative	Herbivore defense	Two species of trees belonging to the Brazil nut family (Lecythidaceae) that emit high levels of S-methylmethionine are colonized by wood-boring beetles at much lower frequency than other tree species in the same family that emit only minute amounts of S-methylmethionine
Methyl salicylate	Hormone	Herbivore defense	Ants of the species Petalomyrmex phylax patrol young but not old leaves of the African tree Leonardoxa africana and attack any phytophagous insects that they encounter. As the young leaves, but not the old leaves, emit high levels of methyl salicylate, the authors hypothesize that the ants are attracted by methyl salicylate and make use of it either as a pheromone or as an antiseptic in their nests

Allelopathy examples

• Leucaena leucocephala, the miracle tree promoted for revegetation, soil and water conservation and animal improvements in India, also contains a toxic, non-protein amino acid in leaves and foliage that inhibits the growth of other trees but not its own seedlings. Leucaena species have also been shown to reduce the yield of wheat but increase the yield of rice. Leachates of the chaste tree or box elder can retard the growth of pangolagrass but stimulate growth of bluestem, another pasture grass.

• For the Apiaceae, the presence of hydroxycoumarins may be an ancestral trait relative to the more toxic linear furanocoumarins, demonstrating that the more complex angular furanocoumarins are the most derived of all three conditions (15, 16). Indeed, Berenbaum & Zangerl (17) showed that variations in the production of furanocoumarins in the Apiaceae plant, Pastinaca sativa, were accompanied by variations in the ability of the herbivorous insect to metabolize these compounds. The high levels of matching between plant and insect phenotypes suggested that the genes conferring an ability to exploit hosts may be tightly linked. Link