Nigel Ian Joyce

Australian redback spiders Latrodectus hasseltii , known for their strong neurotoxic venom, are a quarantine threat for much of the world. Female redback spiders produce a sex pheromone that attracts males of the species, yet the compounds involved in their attraction remain unresolved. Our project set out to identify these compounds and use them to trap male redback spiders as the first step in the development of a pest management/surveillance tool for these spiders. Headspace volatiles from the silk of virgin and mated female redback spiders was collected by solid phase microextraction and analysed by gas chromatography coupled with mass spectrometry. Silk samples were also solvent extracted for analysis by liquid chromatography coupled with mass spectrometry. Comparison with synthetic standards on multiple column phases identified the candidate volatile pheromone components as 2-methylpropanoic acid, ( S )-2-methylbutanoic acid and 2-pyrrolidone, while N -3-methylbutanoyl- O -( S )-2-methylbutanoyl-L-serine was identified as the main candidate short-range cue. Bioassays with a combination of these four compounds showed similar levels of attraction to the natural virgin female’s silk. Field trapping trials using a mixture of all four compounds successfully trapped male redback spiders in New Zealand vineyards.

Consumption of polyphenols and dietary fiber as part of a normal diet is beneficial to human health. In this study, we examined whether different amounts of dietary soluble fiber (pectin) affect the absorption and metabolism of polyphenols from blackcurrant and green tea in rats. After 28 days, the rats fed blackcurrant and green tea with pectin (4 or 8%) had significantly lower body weight gain and food intake compared to the rats fed a control diet. Rats fed a blackcurrant and green tea diet with 8% pectin had significantly higher fecal nitrogen output and lower protein digestibility. No polyphenols were observed in the urine, feces and plasma of rats fed the control diet. Parent catechins and flavonols were absent in urine obtained from all diet groups. Gallocatechin glucuronide was only observed in the plasma of rats fed the blackcurrant and green tea diet without pectin. Meanwhile, epicatechin and catechin gallate were present in the feces of rats fed a blackcurrant and green tea diet with and without 4% pectin. Pectin (4 or 8%) added to the blackcurrant and green tea diet increased the plasma antioxidant capacity in rats. Inclusion of pectin in the diet altered the host absorption and metabolism of polyphenols from blackcurrant and green tea.

Mānuka ( Leptospermum scoparium ) is valued for its unique bioactive honey, but relatively little is known about mānuka nectar and the factors modulating its production. In this study the compositional variability of nectar collected throughout mānuka floral development was measured in glasshouse‐cultivated plants. The total yield of nectar was estimated by rinsing flowers with water and measuring total sugars (°Brix). The concentration of total sugars and of dihydroxyacetone (DHA), the precursor to methylglyoxal and the key mānuka honey bioactive, increased through floral development and maximised just prior to initiation of flower degradation. Similarly, the patterns of several mānuka honey authenticity markers including lepteridine, leptosperin and 3‐phenyllactic acid also followed a similar trend through flower development, suggesting that their biosynthesis was associated with nectar production. Leaf exudates produced as a result of scale insect infestation of some mānuka plants were deficient in the key markers DHA, leptosperin and lepteridine, but did contain 4‐hydroxyphenyllactic acid. This study suggests that the predominant key markers of genuine mānuka are biosynthesised in the floral tissues of the plant rather than elsewhere. For robust analysis and comparison of mānuka nectar yield and composition, sampling needs to take into account the floral developmental stage of the flowers sampled.

Some honeys contain the neurotoxin tutin (1) plus hyenanchin (2), 2-(β-d-glucopyranosyl)tutin (3), and 2-[6′-(α-d-glucopyranosyl)-β-d-glucopyranosyl]tutin (4). These honeys are made by bees collecting honeydew from passionvine hoppers feeding on the sap of tutu plants (Coriaria spp.). We report a LC-MS study showing that all these picrotoxanes are of plant, not insect, origin. Hyenanchin was barely detectable and the diglucoside was not detectable in C. arborea leaves, but tutu phloem sap contained all four compounds at concentrations up to the highest found in honeydew. It is proposed that the diglucoside may function as a transport form of tutin, analogous to sucrose transport in phloem.

Poisonings due to consumption of honeys containing plant toxins have been reported widely. One cause is the neurotoxin tutin, an oxygenated sesquiterpene picrotoxane, traced back to honeybees (Apis mellifera) collecting honeydew produced by passionvine hoppers (Scolypopa australis) feeding on sap of the poisonous shrub tutu (Coriaria spp.). However, a pharmacokinetic study suggested that unidentified conjugates of tutin were also present in such honeys. We now report the discovery, using ion trap LC-MS, of two tutin glycosides and their purification and structure determination as 2-(β-d-glucopyranosyl)tutin (4) and 2-[6′-(α-d-glucopyranosyl)-β-d-glucopyranosyl]tutin (5). These compounds were used to develop a quantitative triple quadrupole LC-MS method for honey analysis, which showed the presence of tutin (3.6 ± 0.1 μg/g honey), hyenanchin (19.3 ± 0.5), tutin glycoside (4) (4.9 ± 0.4), and tutin diglycoside (5) (4.9 ± 0.1) in one toxic honey. The ratios of 4 and 5 to tutin varied widely in other tutin-containing honeys. The glycosidation of tutin may represent detoxification by one or both of the insects involved in the food chain from plant to honey.

Starch phosphorylation is an important aspect of plant metabolism due to its role in starch degradation. Moreover, the degree of phosphorylation of starch determines its physicochemical properties and is therefore relevant for industrial uses of starch. Currently, starch is chemically phosphorylated to increase viscosity and paste stability. Potato cultivars with elevated starch phosphorylation would make this process unnecessary, thereby bestowing economic and environmental benefits. Starch phosphorylation is a complex trait which has been previously shown by antisense gene repression to be influenced by a number of genes including those involved in starch synthesis and degradation. We have used an association mapping approach to discover genetic markers associated with the degree of starch phosphorylation. A diverse collection of 193 potato lines was grown in replicated field trials, and the levels of starch phosphorylation at the C6 and C3 positions of the glucosyl residues were determined by mass spectrometry of hydrolyzed starch from tubers. In addition, the potato lines were genotyped by amplicon sequencing and microsatellite analysis, focusing on candidate genes known to be involved in starch synthesis. As potato is an autotetraploid, genotyping included determination of allele dosage. Significant associations (p<0.001) were found with SNPs in the glucan water dikinase (GWD), starch branching enzyme I (SBEI) and the starch synthase III (SSIII) genes, and with a SSR allele in the SBEII gene. SNPs in the GWD gene were associated with C6 phosphorylation, whereas polymorphisms in the SBEI and SBEII genes were associated with both C6 and C3 phosphorylation and the SNP in the SSIII gene was associated with C3 phosphorylation. These allelic variants have potential as genetic markers for starch phosphorylation in potato.

The traditionally consumed New Zealand native plant nau, Cook’s scurvy grass, Lepidium oleraceum, has a pungent wasabi-like taste, with potential for development as a flavor ingredient. The main glucosinolate in this Brassicaceae was identified by LC–MS and NMR spectroscopy as 3-butenyl glucosinolate (gluconapin, 7–22 mg/g DM in leaves). The leaves were treated to mimic chewing, and the headspace was analyzed by solid-phase microextraction and GC–MS. This showed that 3-butenyl isothiocyanate, with a wasabi-like flavor, was produced by the endogenous myrosinase. Different postharvest treatments were used to create leaf powders as potential flavor products, which were tasted and analyzed for gluconapin and release of 3-butenyl isothiocyanate. A high drying temperature (75 °C) did not give major glucosinolate degradation, but did largely inactivate the myrosinase, resulting in no wasabi-like flavor release. Drying at 45 °C produced more pungent flavor than freeze-drying. Seven other Lepidium species endemic to New Zealand were also analyzed to determine their flavor potential and also whether glucosinolates were taxonomic markers. Six contained mostly gluconapin, but the critically endangered Lepidium banksii had a distinct composition including isopropyl glucosinolate, not detected in the other species.