Studies On The Metabolizes Of The Bitter Princples In Cucurbitaceae Vegetables

Cucurbitaceae plants such as cucumber?melon and watermelon are important vegetables or fruit in China.In the process of cultivation,high temperature,drough or pest attacks lead to bitter fruit of these plants,which in turn seriously affects the commercial quality.This bitter taste was mainly caused by a number of tetracylic triterpenoid constituents,cucurbitacins.It was reported that accumulation of cucurbitacins in the roots and leaves of cucurbit plant play important roles in the risistence of pathogen and pest invasions,moreover,pharmaceutical researchs showed cucurbitacins of great medical potential on anti-tumor cures.However,there are obstacles on the application of these active pharmaceutical ingredients mainly due to its low content in the plants and high difficulty in chemical synthesis.Seeking for an alternative way to solve these problems,intergrated techniques including genenomic,trancriptomic,targeted metabolism and molecular biology were applied to study the biosynthese of cucurbitacins.Studies on the cucurbitacin metabolites in cucumber:On the basis of their physiochemical and spectroscopic evidences,16 cucurbitacin compounds(compounds 1-16)have been isolated and elucidated from 375 kg of fresh cucumber leaves,in which compounds 2?3?4?5?6?7?8?9?10?11?14?15?16 are new compounds.Compounds 5?8?14 might serve as intermidate products in the cucurbitacins biosynthetic pathway.Based on the genenome,transcriptome and variome of cucumber,melon and watermelon,a comparative genenomic analysis combined with genetics,molecular biology and analytical chemistry experiments was carried out,with a result that the biosynthesis clusters of cucurbitacin C,B and E in cucumber,melon and watermelon were unveiled,respectively.Both convergence and divergence are displayed in these genes.By means of mass spectrometry and nuclear magnetic resonance spectroscopy analysis,the functions of three OSC genes(CsBi/CmBi/ClBi),four P450 genes(Cs540,Cs160/Cm160/Cl160,.Cs890/Cm890/C1890,Cm180/Cl180)and three acetyltranferases(Cs700/Cm700/Cl700)were characterized.Among these genes,convergent gene 890 codes a mutifunction enzyme that catalyzes three oxidation reaction steps.Divergent genes 540 and 180 code enzymes that catalyze C19 and C2 oxidation reactions,respectively,which lead to the structural diversity between cucurbitacin C and cucurbitacin B/E.