Abstract
Leaf alcohol, cis-3-hexenol, and leaf aldehyde, trans-2-hexenal, are widely distributed in fresh foliage, vegetables and fruits and are resposible for the characteristic leaf odor. In addition, they are both found in some insect excretions as functioning attractants and repellents. The investigation of leaf alcohol has been carried out by Takei and Ohno et al. since 1938. In this paper, cis-3-hexenal was confirmed in the macerated tea leaves, as being a precursor in the biosynthesis of leaf alcohol, and the process of biosynthesis was clarified linolenic acid and cis-3-hexenal were found in macerated leaves of Thea sinensis and this aldehyde may be produced from linolenic acid by an enzyme contained in macerated tea leaves in the presence of oxygen. This aldehyde was easily isomerized to trans-2-hexenal, and was converted to cis-3-hexenol by alcohol dehydrogenase. During maceration of freshly picked tea leaves, the amounts of trans-2-hexenal quickly increased and were influenced by maceration time, heating, oxygen and the pH. The synthetic activity of cis-3-hexenal was localized in chloroplasts of Thea sinensis leaves. 13-L-Hydroperoxy-linolenic acid also acted as a precursor, but not triglyceride and methylester of linolenic acid. This enzyme system appeared to be tightly bound to the lamellae membranes of chloroplasts. The alcohol dehydrogenase catalyzing cis-3-hexenal to leaf alcohol was purified from Thea sinensis seeds(variety: zairai). The substrate specificity of the ADH for hexenals, hexenols and terpenoids was discussed.
