Showing papers by "Noel W. Davies published in 2011"

Strigolactones promote nodulation in pea.

Abstract: Strigolactones are recently defined plant hormones with roles in mycorrhizal symbiosis and shoot and root architecture. Their potential role in controlling nodulation, the related symbiosis between legumes and Rhizobium bacteria, was explored using the strigolactone-deficient rms1 mutant in pea (Pisum sativum L.). This work indicates that endogenous strigolactones are positive regulators of nodulation in pea, required for optimal nodule number but not for nodule formation per se. rms1 mutant root exudates and root tissue are almost completely deficient in strigolactones, and rms1 mutant plants have approximately 40% fewer nodules than wild-type plants. Treatment with the synthetic strigolactone GR24 elevated nodule number in wild-type pea plants and also elevated nodule number in rms1 mutant plants to a level similar to that seen in untreated wild-type plants. Grafting studies revealed that nodule number and strigolactone levels in root tissue of rms1 roots were unaffected by grafting to wild-type scions indicating that strigolactones in the root, but not shoot-derived factors, regulate nodule number and provide the first direct evidence that the shoot does not make a major contribution to root strigolactone levels.

Quantitative trait loci for foliar terpenes in a global eucalypt species

Abstract: Terpenes are a diverse group of plant secondary metabolites that mediate a plethora of ecological interactions in many plant species. Despite increasing research into the genetic control of important adaptive traits in some plant species, the genetic control of terpenes in forest tree species is still relatively poorly studied. In this study, we use quantitative genetic and quantitative trait loci (QTL) analysis to investigate the genetic control of foliar terpenes in an ecologically and commercially important eucalypt species, Eucalyptus globulus. We show a moderate to high within-family broad-sense heritability and significant genetic basis to the variation in 14 of the 16 terpenes assayed. This is the first report of QTL for terpenes in this species. Eleven QTL influenced the terpenes overall. One QTL on linkage group 6 affected six of the seven different sesquiterpenes assayed (plus one monoterpene), which, in combination with highly significant correlations between these compounds, argues that their variation is influenced by a QTL with pleiotropic effect early in the biosynthetic pathway. We examine the homology of these QTL to those found in a closely related eucalypt, Eucalyptus nitens, and provide evidence that both common and unique QTL influence terpene levels.

Unexpected property of ectoine synthase and its application for synthesis of the engineered compatible solute ADPC

Abstract: A new cyclic amino acid was detected in a deletion mutant of the moderately halophilic bacterium Halomonas elongata deficient in ectoine synthesis. Using mass spectroscopy (MS) and nuclear magnetic resonance (NMR) techniques, the substance was identified as 5-amino-3,4-dihydro-2H-pyrrole-2-carboxylate (ADPC). We were able to demonstrate that ADPC is the product of a side reaction of lone ectoine synthase (EC 4.2.1.108), which forms ADPC by cyclic condensation of glutamine. This reaction was shown to be reversible. Subsequently, a number of ectoine derivatives, in particular 4,5-dihydro-2-methylimidazole-4-carboxylate (DHMICA) and homoectoine, were also shown to be cleaved by ectoine synthase, which is classified as a hydro-lyase. This study thus reports for the first time that ectoine synthase accepts more than one substrate and is a reversible enzyme able to catalyze both the intramolecular condensation into and the hydrolytic cleavage of cyclic amino acid derivatives. As ADPC supports growth of bacteria under salt stress conditions and stabilizes enzymes against freeze-thaw denaturation, it displays typical properties of compatible solutes. As ADPC has not yet been described as a natural compound, it is presented here as the first man-made compatible solute created through genetic engineering.

Detecting traces of methyl eugenol in essential oils: tea tree oil, a case study

Abstract: Methyl eugenol is a naturally occurring flavour and fragrance found in a variety of different food sources, including spices, herbs and fruit and also as a component of natural essential oils. Commonly used oils with more than 0.1% of methyl eugenol include calamus, rosewood, elemi, ylang ylang, cymbopogon, star anise, lovage, verbena, nutmeg, basil, pimento, bay leaf, rose and clove. In addition there are other potential sources of exposure to methyl eugenol, including agriculture, wine consumption and ambient background in air and water. Because high doses of some allyl alkoxybenzenes have induced tumours in rats and mice, use is recommended as either restricted or, in the case of safrole, prohibited. Many reviewers and researchers present clear evidence that these restrictions are excessive, especially those who accept that carcinogenesis is a threshold phenomenon. This paper describes suitable gas chromatographic methods for the determination of trace amounts of methyl eugenol in the essential oil of tea tree, Melaleuca alternifolia, terpinen‐4‐ol type. Published �trace� amounts were interpreted as being as high as 0.3�0.9% by one regulator. Peak assignment by GC‐MS and co‐elution with a standard facilitated the GC‐FID determination of 128 commercial samples. Inter‐laboratory confirmation was achieved using GC‐MS with selected ion monitoring. These determinations indicated that the methyl eugenol content of tea tree oil ranged from less than 0.01% to 0.06% (mean 0.02%), i.e. 20‐fold lower than the regulator�s interpretation and one million times lower than the logarithmic scale levels known to cause carcinomas in rats.

Reassessing the role of YUCCAs in auxin biosynthesis

Abstract: It is remarkable that although auxin was the first growth-promoting plant hormone to be discovered, and although more researchers work on this hormone than on any other, we cannot be definitive about the pathways of auxin synthesis in plants. In 2001, there appeared to be a dramatic development in this field, with the announcement of a new gene,1 and a new intermediate, purportedly from the tryptamine pathway for converting tryptophan to the main endogenous auxin, indole-3-acetic acid (IAA). Recently, however, we presented evidence challenging the original and subsequent identifications of the intermediate concerned.

Glycosidic conjugates of C13 norisoprenoids, monoterpenoids, and cucurbates in Boronia megastigma (Nees).

Abstract: Analysis of a methanolic extract of marc from Boronia megastigma (Nees) using LC-MS (APCI, nominal mass) provided strong evidence for the presence of both glycosides and malonyl glycosides of methyl cucurbates, C13 norisoprenoids including megastigmanes, and monoterpene alcohols. Subsequent fractionation of an extract from the marc using XAD-2 and LH 20 chromatography followed by LC-UV/MS-SPE-NMR and accurate mass LC-MS resulted in the isolation and identification of (1R,4R,5R)-3,3,5-trimethyl-4-[(1E)-3-oxobut-1-en-1-yl]cyclohexyl β-d-glucopyranoside (3-hydroxy-5,6-dihydro-β-ionone-β-d-glucopyranoside); 3,7-dimethylocta-1,5-diene-3,7-diol-3-O-β-d-glucopyranoside; and a methyl {(1R)-3-(β-d-glucopyranosyloxy)-2-[(2Z)-pent-2-en-1-yl]cyclopentyl}acetate stereoisomer (a methyl cucurbate-β-d-glucopyranoside); and provided evidence for 3,7-dimethylocta-1,5-diene-3,7-diol-3-O-(6′-O-malonyl)-β-d-glucopyranoside in boronia flowers.