BIOSYNTHESIS OF FLORAL SCENT...
As mentioned in the introduction, there have been few studies concerning the biochemical synthesis of floral scents, and our recent investigation into the biogenesis of floral scent production in our model organisms C. breweri and snapdragon represent, to our knowledge, the only examples to date in which isolation of enzymes and genes responsible for the formation of scent volatiles in the flower have been accomplished. These results are discussed below. Fortunately, too, many of the volatiles found in floral scents are also synthesized in vegetative tissues under specific conditions (mostly for defense purposes), and some information concerning their biosynthesis is also available. While it cannot be taken for granted that the synthesis of such compounds in vegetative tissue will in all cases be identical (i.e. same reactions, same enzymes) to their synthesis in flowers, and while there is currently no evidence that volatiles synthesized in vegetative tissues are transported into flowers, it is nevertheless instructive to review this information.
Terpenes, especially monoterpenes such as linalool, limonene, myrcene, and trans-beta -ocimene, but also some sesquiterpenes such as farnesene, nerolidol, and caryophyllene, are common constituents of floral scent (Fig. 1A). They are also often found in vegetative tissues, where they serve mostly as defense compounds. In work done mostly with vegetative tissue, but also with daffodil petals, it was found that monoterpenes are synthesized in the plastidic compartment. In this cellular compartment, isopentenyl pyrophosphate (IPP) is derived from the mevalonate-independent "Rohmer" pathway (Lichtenthaler et al., 1997). IPP can be isomerized to dimethylallyl diphosphate (DMAPP), and one molecule of IPP is condensed with one molecule of DMAPP in a reaction catalyzed by the enzyme geranyl pyrophosphate synthase (GPPS) to form GPP, the universal precursor of all the monoterpenes. Similar work with vegetative tissue has revealed that in the cytosol, IPP is derived from the mevalonic acid pathway (McCaskill and Croteau, 1998), and two molecules of IPP and one molecule of DMAPP are condensed in a reaction catalyzed by the enzyme farnesyl pyrophosphate synthase (FPPS) to form FPP, the universal precursor of all the sesquiterpenes (McGarvey and Croteau, 1995).
In the last few years, genes encoding the enzymes responsible for the synthesis of many monoterpenes and sesquiterpenes have been identified and characterized (Bohlmann et al., 1998) (Fig. 1A). However, to date, only the enzyme that catalyzes the formation of the acyclic monoterpene linalool has been characterized in floral tissue. C. breweri flowers emit copious amounts of S-linalool from the petals, stigma, and style (the stigma and style also emit large amounts of linalool oxides), and we were able to demonstrate that linalool was synthesized from GPP in a one-step reaction (Fig. 1A) catalyzed by a monomeric enzyme linalool synthase (LIS) (Pichersky et al., 1994). We were also able to purify LIS from C. breweri stigmata by employing several chromatographic techniques (Pichersky et al., 1995) and to obtain peptide sequences that allowed us to isolate a LIS cDNA clone from a C. breweri flower cDNA library (Dudareva et al., 1996).
The phenylpropanoids, which are derived from Phe, constitute a large class of secondary metabolites in plants. Many are intermediates in the synthesis of structural cell components (e.g. lignin), pigments (e.g. anthocyanins), and defense compounds. These are not usually volatile. However, several phenylpropanoids whose carboxyl group at C9 is reduced (to either the aldehyde, alcohol, or alkane/alkene) and/or which contain alkyl additions to the hydroxyl groups of the benzyl ring or to the carboxyl group (i.e. ethers and esters) are volatiles (Fig. 1B). Our work with C. breweri flowers has now resulted in the identification and characterization of three enzymes that catalyze the formation of floral volatiles from this group: (iso)methyleugenol, benzylacetate, and methylsalicylate. The enzymes are, respectively, S-adenosyl-L-Metiso) eugenol O-methyltransferase (IEMT), acetyl-CoA:benzylalcohol acethyltransferase (BEAT), and S-adenosyl-L-Met:salicylic acid carboxyl methyltransferase (SAMT) (Wang et al., 1997; Dudareva et al., 1998a, 1998b; Wang and Pichersky, 1998; Ross et al., 1999). In addition, we have identified and characterized the enzyme S-adenosyl-L-Met:benzoic acid carboxyl methyltransferase (BAMT), which catalyzes the formation of methylbenzoate in snapdragon flowers (Bushue et al., 1999). cDNAs encoding all of these enzymes have also been characterized.
Thursday, September 30th, 2010
There are numerous references in popular Cannabis literature which claim that Cannabis strains can smell like mango, melon, and even grapes. Well, it might not be their imagination. The odor of cannabis comes from over 120 terpenes (a.k.a. terpenoids fragrance molecules) that are made by the plant(1).
maybe this can help you all out
Do you know what synthesis means? (Got tired of bolding text about half way in.) It means these plants manufacture terpinoids. You're trying to say that dog doo, cat piss and diesel fumes are absorbed and make these fragrances in pot plants. What you cite hasn't got a thing to do with what you assume.
hey disco could you clarify the subtle difference between a floater and a whopper? we should get some good solid info on the page one way or another.
Well, basically... a floater floats. You know, a plausible assumption, hopefully based on something scientific. Doesn't matter if whoppers float or not, they don't flush and just hang around to stink.
