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Title: Studies on the metabolism of phenylpropanoids and related compounds in Capsicum frutescens
Author: Sukrasno, Drs
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1991
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The aim of this project was to investigate the relationship between the metabolism of various secondary metabolites derived from cinnamic acid (phenylpropanoids and related compounds) and the synthesis of capsaicin in fruits and cell cultures of Capsicum frutescens. A variety of compounds derived from cinnamic acid was detected in chilli pepper cultures. However, free phenplics were not detected in callus cultures. Most of the conjugated phenolics were present as O- or ester glycosides. p-Coumaric, ferulic and vanillic acid were detected after release by alkaline, acid or enzymic hydrolysis of water soluble conjugated phenolics. In suspension cultures, several unknown free phenolics were detected in the culture medium. Again as with callus, most phenolics in the cells were present as water soluble conjugates. Over the growth cycle, both callus and suspension cultures accumulated a substantial amount of lignin, but capsaicin was not detected. Apart from capsaicin, a number of water soluble conjugated phenolics were also accumulated in chilli pepper fruits, p- Coumaroyl, caffeoyl and 3,4-dimethyoxycinnamoyl glycosidases (hydroxycinnamoyl glycosides); vanillic acid glycoside; 3- rhamnosyl-quercetin, 7-glycosylluteolin and two unknown flavonoid glycosides were all detected. In addition, several unknown water soluble conjugated phenolics were also present. The proposed free phenolic intermediates in capsaicin biosynthesis were present at vanishingly low levels and only detected after short pulse labelling with [U-14C]-cinnamic acid. The synthesis, accumulation and disappearance of these compounds were studied in relation to the onset of capsaicin synthesis. Before the onset of capsaicin synthesis, the main products of phenyl-propanoid metabolism were the three hydroxycinnamoyl glycosides. During the onset of capsaicin synthesis, fruits were also actively synthesizing lignin and Ce-Ci-phenolic glycosides. There are two major sources of the intermediates for capsaicin, lignin and Ce-Ci phenolic glycosides, 1) the hydroxycinnamoyl glycosides and 2) free phenolics directly synthesized from cinnamic acid. After the onset of capsaicin synthesis, fruits were still actively metabolizing cinnamic acid to produce Ce-Cj phenolic glycosides. Some of these glycosides appeared to be further metabolized during fruit ripening. The metabolism of phenylpropanoids in developing fruits and cell cultures is discussed in relation to the regulation of capsaicin synthesis.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available