Mechanisms for elongation in the biosynthesis of fatty acid components of epi-cuticular waxes

It is known that branched-chain amino acids can serve as precursors to iso- and anteiso-branched components of epi-cuticular waxes. Keto acid deamination products of Val, Leu and Ile are thought to serve as primers which are elongated by fatty acid synthase. However, the origin of elongation carbons has not been studied directly. Nor has the mechanism for formation of odd-carbon-length, straight- or branched-chain, cuticular ester fatty acids or free odd-carbon-length, straight fatty acid components of waxes been characterized. It is not known that α-oxidation of even-length precursors or elongation of odd-length primers is involved in these cases. Here, we present evidence which substantiates the expectation that elongation of branched as well as straight-chain precursors to wax ester acids occurs by fatty acid synthase catalyzed by addition of two carbon units via acetate. Also, we present evidence which indicates that odd-carbon-length acids can result from elongation of odd-carbon-length primers (at least branched), rather than even-length acids shortened by α-oxidation.     

Arabidopsis CER8 encodes LONG-CHAIN ACYL-COA SYNTHETASE 1 (LACS1) that has overlapping functions with LACS2 in plant wax and cutin synthesis

Plant cuticle is an extracellular lipid-based matrix of cutin and waxes, which covers aerial organs and protects them from many forms of environmental stress. We report here the characterization of CER8 / LACS1 , one of nine Arabidopsis long-chain acyl-CoA synthetases thought to activate acyl chains. Mutations in LACS1 reduced the amount of wax in all chemical classes on the stem and leaf, except in the very long-chain fatty acid (VLCFA) class wherein acids longer than 24 carbons (C₂₄) were elevated more than 155%. The C₁₆ cutin monomers on lacs1 were reduced by 37% and 22%, whereas the C₁₈ monomers were increased by 28% and 20% on stem and leaf, respectively. Amounts of wax and cutin on a lacs1-1 lacs2-3 double mutant were much lower than on either parent, and lacs1-1 lacs2-3 had much higher cuticular permeability than either parent. These additive effects indicate that LACS1 and LACS2 have overlapping functions in both wax and cutin synthesis. We demonstrated that LACS1 has synthetase activity for VLCFAs C₂₀–C₃₀, with highest activity for C₃₀ acids. LACS1 thus appears to function as a very long-chain acyl-CoA synthetase in wax metabolism. Since C₁₆ but not C₁₈ cutin monomers are reduced in lacs1 , and C₁₆ acids are the next most preferred acid (behind C₃₀) by LACS1 in our assays, LACS1 also appears to be important for the incorporation of C₁₆ monomers into cutin polyester. As such, LACS1 defines a functionally novel acyl-CoA synthetase that preferentially modifies both VLCFAs for wax synthesis and long-chain (C₁₆) fatty acids for cutin synthesis.     

植物角质层蜡质的化学组成研究综述

角质层是植物与外界的第一接触面,而角质层蜡质则是由位于角质层外的外层蜡质和深嵌在角质层中的内层蜡质两部分构成。植物角质层蜡质成分极其复杂,具有重要的生理功能。综述了有关植物角质层蜡质的化学组成信息,探讨了目前植物角质层蜡质化学成分研究中存在的一些问题,展望了角质层蜡质成分的研究前景。     

The fruit cuticles of wild tomato species exhibit architectural and chemical diversity, providing a new model for studying the evolution of cuticle function

The cuticle covers the aerial epidermis of land plants and plays a primary role in water regulation and protection from external stresses. Remarkable species diversity in the structure and composition of its components, cutin and wax, have been catalogued, but few functional or genetic correlations have emerged. Tomato (Solanum lycopersicum) is part of a complex of closely related wild species endemic to the northern Andes and the Galapagos Islands (Solanum Sect. Lycopersicon). Although sharing an ancestor <7 million years ago, these species are found in diverse environments and are subject to unique selective pressures. Furthermore, they are genetically tractable, since they can be crossed with S. lycopersicum, which has a sequenced genome. With the aim of evaluating the relationships between evolution, structure and function of the cuticle, we characterized the morphological and chemical diversity of fruit cuticles of seven species from Solanum Sect. Lycopersicon. Striking differences in cuticular architecture and quantities of cutin and waxes were observed, with the wax coverage of wild species exceeding that of S. lycopersicum by up to seven fold. Wax composition varied in the occurrence of wax esters and triterpenoid isomers. Using a Solanum habrochaites introgression line population, we mapped triterpenoid differences to a genomic region that includes two S. lycopersicum triterpene synthases. Based on known metabolic pathways for acyl wax compounds, hypotheses are discussed to explain the appearance of wax esters with atypical chain lengths. These results establish a model system for understanding the ecological and evolutionary functional genomics of plant cuticles.     

女贞果实及种子的化学成分

女贞子为木犀科植物女贞 (ＬｉｇｕｓｔｒｕｍｌｕｃｉｄｕｍＡｉｔ.)的果实 ,有滋补肝肾、明目乌发等功效 ,主治眩晕耳鸣、腰膝酸软、须发早白和目暗不明等症 ,女贞子主产江苏、浙江、福建、湖南、广东、广西、江西和四川等省区 ,资源丰富。女贞的化学成分已有报道[1,2 ] ,作者对其全果及种子的化学成分进行较全面分析 ,旨在为其综合开发利用提供科学依据。1　材料和方法1 1　材料和仪器女贞子 2 0 0 0年 11月至 2 0 0 1年 3月分批采自福建省福州市建新郊区、仓山长安山和永泰方广岩。石油醚 (30～6 0℃ )和乙醇等均为分析纯 (上海生化制品…     

Characterization of cis-9 trans-11 trans-15 C18:3 in milk fat by GC and covalent adduct chemical ionization tandem MS

Rumen biohydrogenation of dietary α-linolenic acid gives rise in ruminants to accumulation of fatty acid intermediates, some of which may be transferred into milk. Rumelenic acid [cis-9 trans-11 cis-15 C18:3 (RLnA)] has recently been characterized, but other C18:3 minor isomers are still unknown. The objective of this work was to identify a new isomer of octatridecenoic acid present in milk fat from ewes fed different sources of α-linolenic acid. Structural characterization of this fatty acid was achieved by GC-MS. Analysis of dimethyloxazoline and picolinyl ester derivatives allowed for location of the double bond positions. Covalent adduct chemical ionization tandem mass spectrometry confirmed the positional structure 9-11-15, identical to RLnA, and helped to establish double bond geometry (cis-trans-trans). This new C18:3 isomer could be formed by isomerization of cis-15 bond of RLnA and subsequently converted by hydrogenation to trans-11 trans-15 C18:2, an octadecadienoic acid also detected in this study.