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Emission of floral scent benzenoid/phenylpropanoid compounds in Petunia axillaris increases significantly at night, a change that is primarily determined by the endogenous concentration of these compounds in the corolla. Among wild type P. axillaris plants, there are lines that emit different amounts of scent. To understand how the nocturnal rhythm of floral scent concentrations is controlled, the concentration profiles of metabolites in the scent biosynthetic pathway in two lines of P. axillaris, a strongly scented line and a weakly scented line, are reported. In the strongly scented line, the concentration of a series of compounds from glucose-6-phosphate (G6P) to the scent compounds changed synchronously. In the weakly scented lines, the concentrations of some metabolites including 6-phosphogluconate (6PG) and downstream metabolites of shikimic acid were remarkably lower, suggesting a reduction in metabolism of G6P to 6PG and the metabolism of shikimic acid in the weakly scented line. Nocturnal increases in the concentrations of sucrose, fructose, and glucose were not found in strongly scented line. Nocturnal increases in concentrations of S-adenosylhomocysteine (SAH) and methionine and reductions in the concentrations of S-adenosylmethionine (SAM), a methylation donor to benzenoid-skeletons, were observed only in strongly scented line. It is concluded that the biosynthetic regulation of each step from G6P to the volatile scent benzenoids is performed by, at least in part, concentrations of substrates, and the regulation also affects concentrations of SAM cycle compounds., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The floral scent emission and endogenous level of its components in Petunia axillaris under different conditions (20, 25, 30, and 35 degrees C) were investigated under the hypothesis that floral scent emission would be regulated by both metabolic and vaporization processes. The total endogenous amount of scent components decreased as the temperature increased, the total emission showing a peak at 30 degrees C. This decrease in endogenous amount was compensated for by increased vaporization, resulting in an increase of floral scent emission from 20 degrees C to 30 degrees C. The ambient temperature differently and independently influenced the metabolism and vaporization of the scent compounds, and differences in vapor pressure among the scent compounds were reduced as the temperature increased. These characteristics suggest the operation of an unknown regulator to change the vaporization of floral scent.

Background and Aims: Among the subspecies of Petunia axillaris are various lines emitting sensorially different scents. Analysis of variations in floral scent among genetically close individuals is a powerful approach to understanding the mechanisms for generating scent diversity., Methods: Emitted and endogenous components were analysed independently to gain information about evaporation and endogenous production in 13 wild lines of P. axillaris. A dynamic headspace method was used to collect emitted components. Endogenous components were extracted with solvent. Both of these sample types were subjected to quantitative and qualitative analysis by gas chromatography (GC)-flame ionization detector (FID) and GC-mass spectrometry (MS)., Key Results and Conclusions: Whereas the profiles of emitted compounds showed qualitative homogeneity, being mainly composed of methyl benzoate with quantitative variation, the profiles of endogenous compounds showed both qualitative and quantitative variation. A negative correlation was found between the evaporation ratio and boiling point of each compound examined. Lower boiling point compounds were strongly represented in the emitted component, resulting in the reduction of qualitative variation in floral scent. In conclusion, floral scent diversity results from variation in both the endogenous production and the evaporation rate of the individual volatile compounds.

The mechanism of floral scent emission was studied in Petunia axillaris, a plant with a diurnal rhythm of scent output. The emission rate of each volatile compound oscillated in synchrony with its endogenous concentration, so that the intensity of the floral scent appeared to be determined by the endogenous concentrations. The composition of major volatiles in the flower tissue and the flower headspace showed characteristic differences. A negative correlation was found between the boiling points of the volatile compounds and the ratio of their emitted and endogenous concentrations, indicating that the composition of the floral scent depends directly on the endogenous composition of the volatile compounds. We conclude that in P. axillaris, the physiological regulation of floral scent emission operates not in the vaporization process but in the control of the endogenous concentrations of volatiles through biosynthesis and metabolic conversion.