抄録
Introduction
“Green Odor” emitted by leaves is composed of six unsaturated C6 alcohols and aldehydes with Z- or E-double bonds and two saturated compounds. In response to environmental stimuli, neutral fat, phospho-and galacto-lipids in chloroplasts are hydrolyzed by lipolytic acyl hydrolase to yield α-linolenic and linoleic acids. Then, by lipoxygenase and the hydroperoxide lyase, these acids yield (Z)-3-hexenal and n-hexanal via unstable (S)-13-hydroperoxide intermediates. Finally, by alcohol dehydrogenase these aldehydes are reduced to corresponding alcohols. On the other hand, pyrethrin activity is induced by an original blend of “Green Odor” and (E)-β-farnesene and is formed finally by Lipase/Esterase from chrysanthemoyl CoA and pyrethrolone, respectively. Namely, the pyrethrin forming activities are exactly controlled by the blend ratio of “green odor” and the terpene. This unexpected original finding means that the “Green Odor” is a very important messenger of plant origin.
“Green Odor”
This article describes components, biosynthesis and seasonal changes of the green odor. Green odor emitted by leaves is composed of six unsaturated C6-alcohols, -aldehydes with Z- or E-double bond and two saturated compounds. In these homologues, (E)-2- hexenal is named “leaf aldehyde”, whereas (Z)-3- hexenol is referred to as “leaf alcohol”. Leaf aldehyde was found in fresh green leaves of certain bushes by Curtius T. at Heidelberg University in 1912. Meanwhile, Leaf alcohol was found in fresh tea leaves by my teacher Takei S. at Kyoto University in 1933. In 1960 and 71, I found ｓ(E)-3- and (E)-2-hexenols and then in 1973 and 81, I found (Z)- and (E)-3-hexenals from fresh tea leaves. These eight compounds are collectively regarded as “Green odor”. Until today I have investigated them from a multi disciplinary approach of organic chemistry, biochemistry, molecular biology, aroma-physiology and -psychology.
At first, in the biosynthetic pathway of green odor it should be noted for the unexpected findings that the precursor of green odor does not possess six carbons, such as glucoses, but eighteen carbons; α-linolenic (1) and linoleic acids (2). In response to various environmental stimuli, neutral fat, phospho- and galacto-lipids in tea chloroplasts are hydrolyzed by lipolytic acylhydrolase to result in (1) and (2). Then, by lipoxygenase (LOX) these acids are converted to unstable (S)-13-hydroperoxide-intermediates. Following that, by hydroperoxide lyase (HPO lyase) the cleavage of the single bond between carbon-12 and -13 of these intermediates results in (Z)-3-hexenal and n-hexanal. By alcohol dehydrogenase these aldehydes are reduced to corresponding alcohols. It should be noted that the pathway from lipids to (Z)-3-hexenal is a one way reaction, whereas the alcohol-aldehyde redox reaction is an equilibrium. By this equilibrium the concentration balance between six unsaturated alcohols and aldehydes should result in induced bioactive function. Particularly, the lipoxygenase reaction passes through the complex stereochemical steps, that is the removal of a H proton from C11 in α -linolenic acid to form an (S)-13-hydroperoxide-intermediate. This stereochemical coordination is left rotation of R1->R2->R3- bound to asymmetric carbon-13. (Z)-3- and (E)-2-hexenals produced by LOX and HPO lyase differ largely by plant species.
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