Bambara groundnut (Vigna subterranea (L.) Verdc.) is an important underutilised legume crop, grown mainly by female subsistence farmers in Africa under traditional low input agricultural systems. Bambara groundnut is known as being of high nutritional value, as an atmospheric nitrogen fixer and to possess high levels of drought, pest and disease tolerance. Bambara groundnut is a predominantly self-pollinated crop and is grown as locally adapted landraces. These are expected to exist as non-identical inbred lines and are generally low yielding. Strategies involving genetic analysis of this species could provide important data for breeding programmes that could enhance food security in Africa. A set of 124 SSR primers designed from different library sources were tested to screen a ‘narrow’ genetic cross (F3) and a ‘wide’ genetic cross (F2) . The former is a cross between domesticated landraces (DipC and Tiga necaru) while the latter is a cross between a domesticated landrace and a wild ancestor (DipC and VSSP11). Residual heterozygosity in the F3 ‘narrow’ cross was confirmed to be around 25% based on 33 polymorphic SSR primers, consistent with an F3 population. A ‘narrow’ cross linkage map was constructed for the first time in bambara groundnut using 269 polymorphic markers (236 DArT and 33 SSR). The map consisted of 238 markers in 21 linkage groups of two or more linked markers, totalling 608.1cM and covering a predicted 54% of the bambara groundnut genome, although the high marker-marker linkage (at 89%) suggests a more comprehensive coverage. QTL analysis was carried out for 73 bulked lines of an F3 population and plants were evaluated for traits in a controlled glasshouse suite and a field trial in Indonesia. Data from single plant analysis of the F2 generation of this cross grown in a controlled environment glasshouse was also used. Most of the QTLs detected were clustered on linkage groups 1, 4 and 12. Major QTLs for internode length and biomass dry weight were detected on LG4 and LG1, respectively, for the FutureCrop glasshouse and field datasets. The highest LOD score of 9.7 was detected for peduncle length and was located within the confidence interval for a QTL for internode length locus. Marker locus bgPabg-596774 was detected to be associated with QTL for six traits; node no./plant, pod no/plant, pod weight, seed no./plant, seed yield and biomass dry weight, on LG1 within one LOD score of confidential interval, potentially suggesting pleiotropic effects of a more limited number (or even one) gene(s). One hundred and fifty-nine additional markers (136 DArT and 23 SSR) were used to improve the existing partial ‘wide’ map (141 AFLP, 1 SSR) constructed in an F2 population of 98 plants. A total of 194 markers were assigned to 20 linkage groups spanning a total of 901 cM. The linkage map derived from the ‘wide’ cross (DipC x VSSP11) had an expected genome coverage of 79.6%. An attempt to combine both maps through 32 common markers allowed a common QTL for days to emergence to be detected in both populations in close association with the common DArT markers 601384 and 601748. The main segregating traits were found to be plant spread, internode length, growth habit, peduncle length, pod weight, seed yield and biomass dry weight. Detecting the same QTL positions for a number of traits, suggested that common underlying genes might be responsible. The QTL-DNA marker associations developed in this study could be used practically for MAS in a future breeding program of this crop.

Hyperaccumulator plant species grow in metalliferous soils and accumulate exceedingly high concentrations of metals. They are increasingly studied because of their potential for cleaning up land contaminated with heavy metals, but another aspect of study relates to the reason for hyperaccumulation. The most accepted hypothesis over the last few decades is the ‘elemental defence’ hypothesis, which states that high levels of metals defend the plant against herbivores. Whilst some of the literature is contradictory, some is supportive. An added complication is that many hyperaccumulators belong to the Brassicaceae and produce glucosinolates as organic defences against herbivory. The question to be answered is whether metals or glucosinolates act as the primary defence in these plants and the most recent suggestion is the ‘joint effects’ hypothesis, which states that both classes of chemical work together to benefit the plant and protect it from herbivores. This study investigates these hypotheses and utilized three experimental systems. The hyperaccumulator studied was Thlaspi caerulescens (Gange ecotype) which hyperaccumulates zinc. Plants were grown in a series of glasshouse experiments at a range of soil zinc amendments. There was a positive relationship between soil and foliar zinc; optimum growth occurred at 2000 mg Zn kg-1 soil and this equated to approximately 8000 mg Zn kg-1 shoot, although plants took up as much as 14000 mg Zn kg-1 shoot tissue at higher levels of soil amendment. The herbivore systems studied were generalist thrips (Franklinella occidentalis) and the specialist cabbage whitefly (Aleyrodes proletella). In addition, artificial damage caused by clipping served as a positive control. Four aromatic glucosinolates were extracted from T. caerulescens and two were identified as benzyl and p-OH-benzyl. Glucosinolates were synthesized 32 hours after damage occurred and reached a maximum concentration after 48 hours. Generally, lower concentrations of glucosinolates were observed in plants with higher foliar Zn concentrations and vice versa. However, when plants were subjected to a sustained and heavy herbivore attack, as was the case when thrips infested the plants, glucosinolate production occurred irrespective of foliar Zn concentration. This observation supports the ‘joint effects’ hypothesis, which states that both defences work in tandem and enhance overall defence. Nitrogen was an important component that directed herbivore response. Thrip feeding damage was negatively correlated with foliar nitrogen whilst cabbage whitefly (CWF) benefitted from higher N. Nitrogen was positively correlated with glucosinolate concentrations and glucosinolate content negatively affected the generalist thrips but not the specialist CWF. Data were analysed by accumulated general linear regression and the explanatory model for thrip feeding was C/N ratio + GS + Zn whilst the explanatory model for CWFs was C/N ratio + Zn. Use of the specialist feeder (CWF) allowed for study of the effects of zinc without glucosinolates confounding the results since the CWF was unaffected by foliar glucosinolates. Zinc acted as a defence against CWF but only at high concentrations. The data taken together show that zinc acts as a defence against herbivores that are unaffected by glucosinolates, but only at high concentrations. Zinc also defends the plant against generalist thrips, but glucosinolates are more influential in this case. This might be because of the severe and sustained damage that these plants suffered and systemic effects (i.e. higher concentrations of glucosinolates in undamaged leaves relative to attacked leaves) suggests flexibility in the Zn-glucosinolate relationship. The overall conclusion is in support of the joint effects hypothesis.

The endangered tree Gomortega keule (Mol.) Baillon belongs to the monotypic family Gomortegaceae and is restricted to a small area in Chile. It produces edible fruit and has other uses. However, there is no initiative aimed at its cultivation, presumably because of its difficult propagation. The literature was reviewed for G. keule. In vitro techniques were assessed as a basis for conservation and future domestication. Zygotic embryos, bud, stem, leaf and petiole explants were used in attempts to establish material in vitro. Cultures for shoot and root production involved evaluation of a range of plant growth regulators, concentrations, supplements and environmental conditions. The use of liquid media for tissue culture of G. keule and somatic embryogenesis was also explored. Contamination was the main hindrance to the establishment of cultures, particularly in explants derived from field-collected shoots. The optimum procedure to establish actively growing cultures of G. keule was the use of zygotic embryos as starting material on semi-solid WP medium with 0.1 mg/l NAA and 1.0 mg/l BAP. Stabilization of the material was a constraint, as tissues often showed hyperhydricity. The optimum conditions for proliferation of shoots of G. keule were on WP medium with 0.1 mg/l NAA, 1.0 mg/l BAP, 8 g/l agar, and 20 g/l sucrose at 18ºC. Phenotypically normal shoots developed on WP medium with 2 g/l activated charcoal. Rooting of those shoots was stimulated with a treatment of 1 week on medium with 20 mg/l IBA. Survival of the plants after acclimatization reached 65% after 8 months. Cultures of compact callus and small embryogenic aggregates showed optimum proliferation in liquid MS medium with 20 g/l sucrose, 0.01 mg/l NAA and 0.1 mg/l 2iP. Somatic embryogenesis was observed from compact calli and from small aggregates when they were transferred onto semi-solid MS medium with 0.01 mg/l NAA and 1.0 mg/l BAP. On the same medium, recurrent somatic embryogenesis was also observed directly from the radicle of zygotic embryos. Somatic embryogenesis was induced in shoots after 6.5 months on semi-solid MS medium supplemented with 1.0 mg/l 2,4-D and 1.0 mg/l 2iP. Embryogenic callus proliferated after cryopreservation, which will complement long-term conservation efforts for G. keule. Chromosomes were observed in cells of embryogenic cultures, suggesting diploidy. Using 9 microsatellites, the genetic fidelity of cultured material and the genetic variation were assessed in natural populations of G. keule. Genetic variation was not detected in two embryogenic genotypes cultured in vitro. The populations of plants showed large genetic variation, indicating that conservation efforts must include southern populations.

Petunia hybrida belongs to the family Solanaceae and is an important horticultural crop grown worldwide. Petunia hybrida and one of its parental species, Petunia inflata, are also established model organisms for the study of gametophytic self-incompatibility (SI). All members of the Solanaceae, including Petunia, share the S ribonuclease mechanism of self-incompatibility. The pistil phenotype is determined by an extracellular stylar ribonuclease or “S-RNase”. The pollen phenotype is determined by several S-linked F-box genes (SLFs). All these genes are tightly linked at the S-locus to form an “S-haplotype”. Most cultivated Solanaceae exhibit self-compatibility (SC) as this greatly facilitates the production of seed for annual crops. SC can arise from the breakdown of a functional SI system during domestication and breeding. In this PhD project, we have attempted to develop approaches to control SI in Petunia. Several stocks of Petunia that exhibit SI are available at the University of Nottingham. These carry five distinct S-haplotypes with corresponding S-RNase sequence data, three in P. inflata (PiS3, PiSk1, PiSd) and two in P. hybrida (PhS3L, PhSv). Our approach to engineer SC into lines with SI involved the introduction of a heterologous SLF gene from Antirrhinum hispanicum. It has previously been shown that transformation of P. hybrida with the AhSLF-S2 gene under the control of a pollen-specific promoter (LAT52) causes SI to breakdown (Qiao et al, 2004b). This is explained as a “competitive interaction”. We have obtained the LAT52: AhSLF S2 construct used by the group of Prof. Yongbiao Xue (Chinese Academy of Sciences, Beijing). In addition, we have obtained three constructs containing other SLF family members (AhSLF-S2C, AhSLF-S4D and AhSLF-S1E) all expressed specifically in pollen (Zhou et al, 2003). The aim of this project is to extend the analysis of these heterologous SLF genes to test whether they offer a general approach to overcome SI in P. hybrida. This involved using the wider range of S haplotype stocks available (5) and the full range of constructs available (4). Initial experiments confirmed the genotype and phenotype of the P. inflata stocks. Crosses were made between P.hybrida and P.inflata and the resulting F1 progeny were tested for SI. It was noticed that some progeny inheriting the PiSd allele of P. inflata have a tendency towards SC, but others have a stable SI phenotype. This observation was further analysed in the F2 generation and based on reciprocal crosses it was determined that the pollen part of the PiSd allele had lost its function resulting in compatibility. Prior to transformation the constructs were checked by sequencing plasmid DNA and colony PCR products using specific primers. The expected fusions of SLF gene and LAT52 promoter were confirmed. An established protocol was used to transform the S3/Sv genotype of P. hybrida. Different numbers of transgenic plants have been identified for each construct (6, 17, 3 and 11 for AhSLF-S2, AhSLF-S2C, AhSLF-S1E and AhSLF-S4D respectively). However, in the T0 generation competitive interaction was not observed. Transgenic plants were crossed with Petunia inflata but F1 hybrid plants remained SI. Transgenic plants obtained for AhSLF-S2 and AhSLF-S1E were analysed in the T1 generation. In spite of the fact that all plants derived from PhSLF-S2 remained SI, one plant derived from AhSLF-S1E became SC. It was predicted that the compatibilty in this particular plant arises as a result of homozygosity. Based on this observation a hypothesis was proposed for a relationship between compatibility and homozygosity and several techniques were used to test this hypothesis. It has been concluded that there is a relationship between homozygosity and transgene behaviour in specific epigenetic situations.

Momordica balsamina (inkakha) and M. foetida (inshubaba) are used in several countries, including Swaziland, both for food and as a traditional medicine to treat and cure several diseases. Systematically investigating their bioactivities and identifying the compounds responsible for the curative properties could greatly extend the therapeutic applications of these plant species. The aim of the present study was to investigate antimicrobial, anti-proliferative activities and biochemical composition of extracts of Momordica plants. Methanol-water extracts of M. balsamina and M. foetida leaf, stem and fruit were screened for antimicrobial activity against a range of bacteria. Gram-positive bacteria were found to be the most sensitive to Momordica extracts particularly leaf extracts. The lowest minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were from leaf extracts of M. balsamina and MBC was determined to be 2.5 mg/mL against L. monocytogenes. Following fractionation of Momordica extracts using solid phase extraction (SPE) the methanol eluted fraction showed antimicrobial activity against L. monocytogenes and S. aureus strains which was comparable to the antimicrobial activity of crude extracts. The anti-proliferative activity of methanol-water extracts, of M. balsamina and M. foetida leaf, was tested against human liver hepatocellular carcinoma (HepG2) cells. Leaf extracts from both M. balsamina and M. foetida displayed anti-proliferative activity at concentrations of 0.25 and 1mg/mL, respectively. Biochemical analysis of the extracts was carried out through Fourier transform infrared spectroscopy, high performance liquid chromatography, nuclear magnetic resonance and liquid chromatography-mass spectrometry analysis. This study demonstrated the highest total phenolic content in leaf extracts with a range of 34.39 to 47.94 mg GAE/g, followed by stem extracts with a range of 21.02 to 26.19 mg GAE/g and least by fruit extracts with a range of 3.97 to 12.97 mg GAE/g. A good correlation was revealed between the antimicrobial activity of Momordica extracts and total phenolic content suggesting that phenolic content could be partly responsible for the antimicrobial activity of the extracts, but this remains to be confirmed. These results could indicate the potential use of Momordica plants as antimicrobial agents as well as anti-cancer agents and also provide the basis for the isolation and identification of the biologically active substances in these extracts.

Lignans are the most important secondary metabolites known in Podophyllum hexandrum and Diphylleia cymosa. Tissue cultures studies were carried out in order to preserve and increase these germplasms. Somatic embryogenesis in both species was obtained and confirmed histologically. In D. cymosa, somatic embryos were induced from leaf and petiole-derived callus. The formation of abnormal embryos, with fused cotyledons, was influenced by the growth regulators used. Embryo maturation was confirmed histochemically through the identification of starch granules in the cotyledons. Regeneration was dependent on the culture media. Somatic embryogenesis in P. hexandrum was achieved through embryogenic cell suspension cultures from root-derived callus. Organogenesis via adventitious bud formation led to plant regeneration in liquid medium. Phenotypically normal plants were recovered. The regenerant showed the somatic chromosome number of 2n=2x=12, although some chromosomes were morphologically abnormal. The recalcitrance of P. hexandrum towards Agrobacterium-mediated transformation was demonstrated with different strains of both A. tumefaciens and A. rhizogenes. The presence of cytotoxic lignans in P. hexandrum may have a role in the inactivation of the bacteria. Aryltetralin lactone lignans isolated from rhizomes and roots of P. hexandrum and characterized by spectroscopic methods were used as standards in phytochemical studies of D. cymosa. Enzymic hydrolysis of the lignan glycosides, followed by reverse-phase HPLC, allowed the screening of lignans in leaf tissues, calli and cell suspension cultures. The antitumour lignin, podophyllotoxin was detected in young leaves of cultivated plants and. for the first time, in vitro petiole-derived calli. Flavonoids were investigated in leaf extracts of Passiflora edulis, P. incarnate and their somatic hybrids. Fractionation of the crude extracts of P. incarnata and the somatic hybrid SHI led to the isolation of compounds with skeletal type of C-glycosylflavones. Isoorientin was identified in P. edulis. whilst vitexin was found in P. incarnata by TLC. All the somatic hybrids showed similar consistant flavonoid banding profiles. Isoorientin and vitexin were detected in the somatic hybrids. HPLC of the parental species revealed a distinct pattern of flavonoids. Isoorientin was clearly detected in P. edulis, whereas isovitexin was present in both species. The fingerprint patterns of the HPLC separations of the flavonoids were similar in all the somatic hybrids, probably due to the clonal nature of the plants analysed. They appeared to be more closely related to P. incarnata than to P. edulis. However, they also exhibited flavonoids intermediate between those of the parental species. This is the first report of the biosynthesis of isoorientin and isovitexin in these novel somatic hybrids and could provide information about their inheritance.

Fruit texture is a quantitative trait believed to be determined by a number of genetic loci. In order to identify genes in strawberries that are specifically associated with texture a cross was made between a cultivar with firm fruits and a cultivar with soft fruits. The resultant population of 269F plants produced ripe fruits whose firmness values differed over a five-fold range. Pools of twenty plants having either the softest or firmest fruits were analysed by two methods. The first, suppressive subtractive hybridisation initially indicated that many genes were differentially expressed in fruits from both the firm and soft pools. Differential hybridisation of 80 subtracted cDNA clones from each pool with the cDNA subtracted from each pool showed that many of the cDNAs were common to firm and soft fruit. When the subtracted cDNAs were hybridised with unsubtracted eDNA several clones from each pool appeared to be enhanced. However, northern analysis was unable to confirm these data. The second method used cDNA-AFLP to detect differentially expressed genes in the pools of firm and soft fruit. Using one set of amplification primers, bands corresponding to 27 cDNA fragments specific to either firm or soft fruit pools were resolved on a polyacrylamide gel. These fragments were cloned and sequenced but they had no obvious homology with genes associated with cell wall metabolism. Northern anlaysis indicated that the cloned cDNA-AFLP fragments represented polymorphisms unrelated to texture. One cDNA clone, AFLP-S 13, appeared to have higher levels of the corresponding transcript in fruits from the soft parent and soft pool. Although this clone was upregulated during ripening its expression was neither fruit specific nor correlated with texture. The expression of genes associated with cell wall metabolism including cell. cel2 and expansin was also investigated in the segregating population.

A new leuco-anthocyanidin, (+)-7,4'dihydroxyflavan- 3:4-diol has been isolated from the heartwood of Guibourtia coleosperma. The heartwood extractives were fractionated by enrichment procedures involving fractional precipitation and Craig partitioning, to give a high RF (subscript) low molecular weight fraction containing the above leuco -anthocyanidin. This was further fractionated by "preparative" paper chromatography . The leuco-anthocyanidin was amorphous and present in low proportion (0.004%) in the wood. On boiling with alcoholic hydrochloric acid the compound gave an anthocyanidin which was identified as 3,7,4'-trihydroxyflavylium chloride. The degradation products formed by alkali fusion, on a micro-scale, were resorcinol and ♭-resorcylic acid, and also p (underscore)-hydroxybenzoic acid. This indicated resorcinol and phenol A and B nuclei respectively. The formation of amorphous dimethyl ether and tetra-acetoxy derivatives indicated two phenolic and two alcoholic hydroxyl groups. The above indicates that the compound was 7,4'-dihydroxyflavan- 3:4- diol and a molecular weight estimation showed it to be monomeric. Comparison of the infrared absorption spectra of the natural dimethyl ether with synthetic (±) dimethoxyflavan- 3:4-diol, to which a tentative 2:3- trans- 3:4-cis conformation had been assigned (Phatak and Kulkarni 94), showed close identity. Crystalline (±)-7, 4 '-dihydroxyflavan- 3:4 - diol was synthesised by catalytic hydrogenation over platinum oxide of the corresponoing (±) -7,4'-dihydroxyflavanonol. The flavanonol was synthesised by sodium hyposulphite reduction of the 7,4 ' -dihydroxyflavonol. The infrared absorption spectra of the natural and synthetic diols were similar but not identical. Chromatographic evidence showed the apparent identity of the synthetic and natural flavan- 3:4- diols, and two possible configurations were assigned for the natural flavan-3:4-diol. The new leuco-anthocyanidin was observed to form an O(underscore)-ethyl ether derivative on manipulation in ethanol. A monomeric leuco- fisetinidin from the heartwood was identified, by two dimensional paper chromatography, as (+) - mollisacacidin. The condensed tannins found also in the heartwood of G.(underscore)- coleosperma appear to be polymeric forms of leuco - fisetinidin and leuco - guibourtinidin. These polymeric tannins form a large proportion of the heartwood extractives and furnish high yields of fisetinidin and guibourtinidin chlorides on boiling with alcoholic hydrochloric acid. Examination of some other members of the Guibourtia spp . by paper chromatography showed that only G (underscore). coleosperma contained the new leuco - anthocyanidin as well as a leuco - fisetinidin. G. (underscore) tessmannii and G. (underscore) demeusii heartwoods contained only leuco-fisetinidin and the related polymers and a close chemical relationship to G.(underscore) coleosperma is thus apparent. G.(underscore) arnoldiana on the other hand is not chemically interrelated with the above members since it appeared to contain only leuco - cyanidin. (±) - 7,4 ' -Dihydroxyflavan- 4-ol was synthesised by hydrogenation of the corresponding flavanone over platinum oxide. Observations were made regarding its reddenig and ease of condensation.

Thesis (Ph. D.)--University of Chicago, Dept. of the Geophysical Sciences, June 2000. / Includes bibliographical references. Also available on the Internet.

With the increasing evidence of climate change in the coming decades, adaptive mechanisms present in nature may permit crop survival and growth on marginal or saline soils and is considered an important area of future research. Some subspecies of Restharrow; O. repens subsp. maritima and O. reclinata have developed the remarkable ability to colonise sand dunes, shingle beaches and cliff tops. α-onocerin is a major component within the roots of Restharrow (Ononis) contributing up to 0.5% dry weight as described by Rowan and Dean (1972b). The ecological function of α-onocerin is poorly understood, with suggestions that it has waterproofing properties, potentially inhibiting the flow of sodium chloride ions into root cells, or preventing desiccation in arid environments. The fact that alpha-onocerin (a secondary plant metabolite) biosynthesis has evolved a number of times in distantly related taxa; Club mosses, Ferns and Angiosperms, argues for a relatively simple mutation from non-producing antecedents. No direct research has been reported to have investigated the biosynthetic mechanism towards α-onocerin synthesis via a squalene derived product originally characterised by Dean, and Rowan (1972a). A bi-cyclisation event of 2,3;22,23-dioxidosqualene by an oxidosqualene cyclase, may provide plants with an alternative mechanism for synthesising a range of triterpene diol products via alpha-onocerin (Dean, and Rowan, 1972a). This mechanistic possibility presented the opportunity to investigate the biosynthesis of α-onocerin using a multi-disciplinary approach. This thesis presents supporting data, that α-onocerin is a derivative of 2,3;22,23-dioxidosqualene via an oxidosqualene cyclase. Genetic markers were developed for Ononis versions of squalene cyclase, squalene epoxidase and a putative oxidosqualene cyclase. It was determined that squalene epoxidase; At4g37760 (SQE3), from A. thaliana showed the highest level of amino acid sequence conservation with the O. spinosa version. SQE3 is known to cyclise 2,3;22,23-dioxidosqualene (Rasbery et al., 2007). Based on amino acid sequence alignments and predictive protein modelling a partial putative oxidosqualene cyclase isolated from O. repens III subsp. maritima is likely to be an Ononis version of β-amyrin synthase rather than a multifunctional oxidosqualene cyclase. Further functional characterisation studies are needed. Methods were developed for analysing the transcriptome and metabolome in Restharrow which will aid future functional characterisation studies. Within O. spinosa root SQE3 was highly expressed. In contrast SQE3 was expressed at low levels in O. spinosa leaf and O. pusilla root and leaf. This data was supported by metabolomic profiling of five species of Restharrow; O. spinosa, O. repens, O. repens subsp. maritima, O. pusilla and O. rotundifolia. Triterpenes α-onocerin and 2,3;22,23-dioxidosqualene were not present in O. rotundifolia and O. pusilla. Where 2,3;22,23-dioxidosqualene was present in plant extracts, α-onocerin accumulation was also detected. O. pusilla and O. spinosa can be utilised for studying the occurrence of alpha-onocerin within plants. The data presented in this thesis provides the necessary background information providing targets for functional expression studies of squalene epoxidases and oxidosqualene cyclases from Restharrow. In summary the results in this thesis support the hypothesis proposed by Dean and Rowan (1971). There is good evidence to suggest the ability of Restharrow to cyclise alpha-onocerin, may be dependant on the availability of 2,3;22,23-dioxidosqualene as the primary precursor. This was shown in development, tissue specific, ecotype and cell free enzyme analytical chemistry assays. There was little evidence to suggest a single specific oxidosqualene cyclisation event was primarily responsible for alpha-onocerin biosynthesis. The work also presents evidence to suggest that differences in the squalene epoxdiase sequence and transcription signals may affect the plants ability to cyclise alpha-onocerin. This may have ecological implications and allow plants to adapt to their environment by providing and alternative route to biosynthesising membrane constituents via an alternative substrate specific mechanism.