Attack by the specialist herbivore, Manduca sexta, on its native host Nicotiana attenuata Torr. ex Wats. produces a dramatic ethylene release, a jasmonate burst, and a suppression of the nicotine accumulation that results from careful simulations of the herbivore's damage. Methyl-jasmonate (MeJA) treatment induces nicotine biosynthesis. However, this induction can be suppressed by ethylene as pretreatment of plants with 1-methylcyclopropene (1-MCP), a competitive inhibitor of ethylene receptors, restores the full MeJA-induced nicotine response in herbivore attacked plants (

SummaryCaterpillar-induced ethylene emissions play an important role in plant-herbivore interactions. The ethylene burst that ensues after attack exceeds wound-induced ethylene emissions, but the mechanisms responsible remain unknown. Adding larval oral secretions (OS) to wounds mimics this ethylene burst. We demonstrate that fatty acid-amino acid conjugates are the responsible elicitors in Manduca sexta OS, and identify genes that are important in OS-elicited ethylene biosynthesis and perception in the larvae's host, Nicotiana attenuata, by examining the consequences of gene silencing on OS-elicited ethylene emissions, as quantified by photo-acoustic spectroscopy. OS elicitation increased transcript accumulation of ACC synthase (ACS), virus-induced gene silencing of ACS halved the OS-elicited ethylene release, and ACC supplementation to ACSsilenced plants restored ethylene emissions, demonstrating that ACS activity limits the rate of release. Silencing three wound-or OS-elicited ACC oxidase (ACO) genes with an ACO consensus fragment abolished the OS-elicited ethylene release. Virus-induced gene silencing of each ACO individually revealed that only NaACO2a and NaACO3 regulate the OS-elicited ethylene release. Transforming plants with various etr1-1 constructs rendered them differentially 'deaf' to ethylene, and dramatically increased the OS-elicited ethylene burst, largely without regulating the transcripts of biosynthetic genes. The volume of the OS-elicited ethylene 'scream' was proportional to the plant's deafness, as determined by 1-MCP treatments. We conclude that the OS-elicited ethylene burst is tuned by a tag-team of transcriptional responses and ethylene perception. Ethylene signaling is shown to be essential in regulating two traits that are important in the N. attenuata-M. sexta interaction: OS-induced nicotine levels and floral longevity.

Early white winemaking operations are known to affect the extraction of grape skin compounds into the juice fraction, which will dictate their concentration in the resulting wine. Grape skin contact and the amount of pressure applied during grape pressing affect the extraction of varietal aromas located in the skins. Compounds such as the polyphenols and glutathione, with antioxidant properties involved in juice oxidation processes and white wine stability, are also affected. The present study evaluates how grape skin contact and the amount of pressure applied during grape pressing affect the levels of S-(3-hexan-l-ol)cysteine (3MH-S-cys, a key grape-derived precursor to the volatile thiol 3-mercapto-hexanol (3MH), which is reminiscent of passion fruit aroma); 2-methoxy-3-isobutylpyrazine (IBMP, with a capsicum-like descriptor); phenolic compounds; and glutathione in Sauvignon Blanc juice. The study was conducted using grapes obtained from commercial Marlborough (New Zealand) vineyards, using both commercial and laboratory grape-processing procedures. Immobilized metal ion chromatography was used to isolate the 3MH- S-cys precursor from the juices. The isolated precursor was then volatilized by trimethylsilylation and analyzed using gas chromatography/mass spectrometry (GC/MS). IBMP was analyzed by GC/MS after solvent extraction, and a high-performance liquid chromatography method was used for the quantification of phenolic compounds and glutathione. 3MH- S-cys levels were seen to increase in juice fractions obtained from a winery press operating at higher pressures. The increase was attributed to the cumulative effect of longer skin contact time and the amount of pressure applied. The highly water-soluble IBMP was less affected by the amount of pressure applied during commercial grape pressing. Additional information was generated by the specific assessment of skin contact and applied pressure during grape pressing in a laboratory trial. In this trial, a long (32 h) skin contact time resulted in a greater release of varietal aroma compounds, 3MH- S-cys, and IBMP into the juice, and the concentration was further raised by increasing the pressure applied during pressing. However, for both experiments, the extraction of the varietal aroma compounds was offset by a clear increase in the juice oxidative potential, seen by a decline in glutathione content, a natural grape antioxidant, and an increase in particular oxidizeable polyphenol compounds, which may cause the must or wine to brown and lead to a loss of varietal aromas.