Jms589-Summary+of+Props+Article

=Effect of Temperature on the Floral Scent Emission and Endogenous Volatile Profile of Petunia axillaris= https://www.jstage.jst.go.jp/article/bbb/72/1/72_70490/_pdf http://dx.doi.org/10.1271/bbb.70490

Abstract:
The floral scent emissions and endogenous level of its components in Petunia axillaris under four different temperatures were determined. The endogenous amount of scent components decreases as the temperature increased, where the vaporization increased. These properties suggest a n unknown regulator that changes vaporization.

=Article= -Floral scented compounds come from within the flowers and tend to have high vapor pressures. These floral scented compounds have boiling points of 150-350 degrees C, thus they are present in liquids, solids, or in solution in tissues. The endogenous amount of floral scent reflect the metabolic and vaporization process.

-Techniques have advanced the understanding of floral scent metabolism. Aromatic scent compounds are produced from phenyl-alanine through multiple pathways. Certain genes that control floral scents have been cloned; ODORANT1 has been identified in petunia and biosynthesis and conversion of compounds is thus important for regulating the amount of floral scents.

-While the metabolic process is understood, little is known about vaporization for floral scents because it does not occur at room temperature. By analyzing P. axillaris, it could give insight on how temperature effects the floral scent of horticultural plants, since floral scent can be controlled in these flowers by physical regulation.

-The effect of temperature on floral scent emission should be studied with regards to metabolism and vaporization because it is unclear whether or not scent emission is a result of either process individually or a combination of both. Different temperatures influenced the metabolism and vaporization of scent compounds differently in P. axillaris.

Materials and Methods
-P. axillaris was the plant material used and was raised from seeds from a natural population, from Uruguay, and propagated for two months. Prior to the experiment, the plants were acclimatized for a minimum of one week in a chamber at either 20, 25, 30, or 35 degrees C.

-The emitted volatile scent compounds were retrieved for one hour, from day old flowers, including stem and leaves, using the headspace method: flowers were covered with bags while constant air was filtered through the bag. After, the flowers were removed of calyx and the concentration of extracted scent compounds were calculated.

-These scent compounds were extracted four times using 5mL each of alternating pentane and diethyl ether. After ethyl decanoate was added, as a standard, the extracts were dried using anhydrous sodium sulfate and concentrated in a water bath at 40 degrees C.

-After extracting the volatile compounds and flower tissues without calyx, they were frozen using liquid nitrogen and then grounded up to be extracted twice with 5mL each of pentane, in a microwave for 20 seconds. It was then dehydrated with anhydrous sodium sulfate and concentrated again in the water bath at the same temperature.

-GC-MS was used, with a column oven starting at 45 degrees for two minutes and then increasing by increments of 3 degrees until 220 degrees was reached. The GC-MS was monitored using a flame ionization detector and the amount of each volatile compound was determined by comparing to the peak area of an internal standard as well as a library search, provided by GC-MS program.

Results
- The flowers had a similar diameter under all three temperatures but was only slightly smaller at 35 degrees C; there was no other major change in their appearance.

-By GC-MS, ten volatile compounds were identified: benzaldehyde, benzyl alcohol, benzyl benzaote, eugenol, iso-eugenol, methyl benzaote, methyl salicylate, phenyl acetaldehyde, 2-phenyethanol, and vanillin. Where methyl benzoate, iso-eugenol, and benzyl benzoate totaled more than 80% of the constituents at every temperature.

-The amount of the compounds identified increased with temperature but decreased at 35 degrees; the only exception was benzaldehyde in which the emission decreased as temperature increased.

-There was a correlation between the natural log of the emission ratio and boiling point at each temperature, in which the slope reduced as the temperature increased.

Discussion
-The floral scent, volatile compounds, found in P. axillaris, at all temperatures were aromatic compounds extracted from phenylalanine, in which their amounts decreased with increasing temperatures. It was found that the increase in temperature reduced the biosynthetic activity yet promoted metabolic conversion.

-Anthocyanin, a floral pigment extracted, normally decreased in other plants with increasing temperatures, and might be similar to the mechanism in P. axillaris since the endogenous amount of scent compounds decreased. This concludes that each metabolic network responsible for floral scents was differently affected by temperature.

-The extracted compounds' amounts reached a maximum at 25 and 30 degrees C, which most likely relates to the emission ratio, because the difference in temperature dependence between the endogenous amount and emission ratio show that temperature independently influenced the metabolism and vaporization of the compounds. This the effect of temperature on floral scent emission should be studied independently for metabolism and vaporization.

-The emission ration, however, negatively corresponded to the boiling point at all temperatures. Ultimately, this shows that the differences in vaporization between the scent compounds decreased at temperature increased. The reasoning for contradictory data at 35 degrees C is a result of the difference in diameter because the area in which the compounds could evaporate was smaller.

-Overall, there was no direct relation between vapor pressure and boiling point and there still remains many unanswered questions in understanding how floral scents evaporate. The next step is to analyze microscopic and biochemical approaches.