James McDaniel: Rosa palustris, a Model Species for Fragrance Investigations
Rosa palustris, a Model Species for Fragrance Investigations James McDaniel and Nancy Cowden, Ph.D., Biology Department and Priscilla Gannicott, Ph.D., Chemistry Department and DeAnne Moore Lynchburg College, 1501 Lakeside Drive, Lynchburg, VA 24501
ABSTRACT• The flowering plants Rosa palustris and Rosa palustris var. scandens have distinguishing characteristics such as their habitat and floral anatomy that set them apart. With a five-petaled bloom, R. palustris thrives in swamps or bogs while R. palustris var. scandens is a double-petaled hybrid cultivated for gardening purposes. From June 2010 to June 2011, we investigated the fragrance composition of these flowering plants. A total of 16 samples were collected from R. palustris and R. palustris var. scandens flowers, using solid-phase microextraction (SPME). Total ion chromatograms were produced by a Thermo electron-focus GC/DSQ MS and XCalibur 1.4 software. Mass spectra were obtained from these chromatograms using NIST MS Search 2.0, which allowed us to identify the volatile organic compounds found in these roses. The most abundant compounds found in R. palustris were 1-(R)-alpha-pinene, phenylethyl alcohol, geraniol acetate, trans-geraniol, and cis-geraniol. Those found in R. palustris var. scandens were phenylethyl alcohol, nonanal, 1-(R)-alpha- pinene, and cis-geraniol. Ultimately, characterizing their fragrance signatures is important because it has the potential to aid in selecting fragrant varieties for new hybridizing endeavors in the future.
INTRODUCTION• The genus Rosa includes approximately 200 species as well as more than 18,000 cultivated varieties (Guterman, 2002). Species roses, such as Rosa palustris, have been cultivated for centuries to produce hybrid varieties. In the garden setting, hybrid varieties known as cultivars are selectively propagated for desirable characteristics. Some of these desirable characteristics include the following: long vase life, flower shape, color, and “scent” (Shalit, 2003). In the field, it is visually evident that the garden cultivar Rosa palustris var. scandens is propagated for its flower shape because it has more petals than R. palustris and no prickles whereas the native rose, R. palustris, has only a single bloom and curved prickles (Figs. 1 and 2). It is not quite clear, however, whether or not R. palustris var. scandens is propagated for its “scent” because its fragrance composition has not been characterized previously. “Scent” is important because it is an ancient connection among flowering plants, their pollinators, and enemies (Raguso, 2008).• We not only investigated the fragrance composition of the native wetland species, R. palustris, but also that of the garden cultivar R. palustris var. scandens as a means of comparison. This summer, we plan to further examine the relationship between the fragrance of R. palustris and R. palustris var. scandens as well as their pollinators. By examining this relationship, pollination efficiency can be examined over time, which can be dependent upon visitor abundance, visitor activity, and pollen loads deposited on receptive stigmas and seed set (Yeboah Gyan, 1987). Determination of pollination efficiency coupled with the characterization of the fragrance of each rose could aid in selecting fragrant varieties for new hybridizing endeavors in the future.
INTRODUCTION Figure 1. Rosa palustris in a wetland, Figure 2. Rosa palustris var. Bedford Co., VA. scandens in the Antique Rose Emporium, Brenham, TX.
MATERIALS AND METHODS• In 2010 and 2011, the month of June provided us with the opportunity to collect a total of 15 floral fragrance samples from Rosa palustris at the Claytor Nature Study Center, Bedford Co., Virginia. Additionally, one floral fragrance sample of Rosa palustris var. scandens was obtained in June of 2011 at the Old City Cemetery, Lynchburg, Virginia. All of the samples were collected using static-headspace, solid-phase microextraction (SPME) via 50/30 mm DVB/carboxen fibers (SUPELCO Analytical, Bellefonte, Pa.). To collect the samples, theSPME fibers were placed above the floral headspace of each individually bagged bloom (Figure 3). Over the course of an hour, the SPME fibers absorbed the volatile organic fragrance compounds emitted from each rose bloom. After an hour had passed, these fibers were retracted back into their protective casings and transported to Lynchburg College for further analysis on the same day that the samples were obtained.• At Lynchburg College, desorption of the volatile organic compounds was achieved in the laboratory by inserting the individual samples into the injection port of a Thermo-Scientific Focus GC/DSQ MS set at 250°C. Total ion chromatograms were analyzed to confirm the identity of each volatile organic compound by comparing mass spectra to a NIST MS Search 2.0 database.
MATERIALS AND METHODS Figure 3. Static-headspace SPME field sampling technique.
RESULTS• When comparing the Rosa palustris samples, it became evident that some of them not only differed in the number of volatile organic compounds that were present, but also by the relative percentages (percent area and percent height) of each compound.• Although other compounds were identified using the NIST MS search 2.0 database, we consistently identified 1-(R)-alpha-pinene, phenylethyl alcohol, cis-geraniol, trans-geraniol, and geraniol acetate as the volatile, organic fragrance compounds that constituted the greatest relative percentages out of all of the fragrance compounds found in R. palustris (Figs. 4 and 5). In addition, the NIST MS search 2.0 database determined that 1-(R)- alpha-pinene, nonanal, phenylethyl alcohol and cis-geraniol constituted the greatest relative percentages out of all of the fragrance compounds found in R. palustris var. scandens (Figs. 6 and 7).
RESULTSRT: 8.00 - 18.00 12.69 NL: 100 5.20E8 95 14.70 TIC F: MS 90 rcarolina628 10mix1 85 Phenylethyl alcohol 80 75 Trans-geraniol 70 65 60 Cis-geraniol 16.42 55 50 14.33 45 40 35 30 Geraniol acetate 25 20 15 14.95 10 13.77 15.18 10.40 11.40 17.18 5 8.62 9.43 13.20 15.27 9.59 0 8 9 10 11 12 13 14 15 16 17 18 Time (min) Figure 4. A representative total ion chromatogram Figure 5. Relative percentages of all fragrance of a Rosa palustris SPME sample (6/28/2010). compounds found in a fresh Rosa palustris bloom (6/28/2010).
RESULTSRT: 8.00 - 18.00 13.63 NL: 100 1.16E8 Phenylethyl alcohol 95 TIC F: MS 90 PalustrisSca ndens06032 85 011mixedpg 13.32 1 80 75 70 65 60 55 50 Nonanal 45 40 Cis-geraniol 35 30 16.26 (R)-alpha-pinene 25 14.78 20 13.93 15.74 17.57 15 10.44 12.40 17.19 10 9.51 11.28 12.72 15.29 5 8.53 9.71 16.40 0 8 9 10 11 12 13 14 15 16 17 18 Time (min) Figure 6. A representative total ion chromatogram of a Figure 7. Relative percentages of all Rosa palustris var. scandens SPME sample (6/3/2011). fragrance compounds found in a fresh Rosa palustris var. scandens bloom (6/3/2011).
DISCUSSION• More than 400 volatile, organic compounds are known to be related to rose scent (Shalit, 2003). Among these are alcohols described as having a “rose like” odor that are frequently found in rose species (Chemicalland21.com, 2010). Phenylethyl alcohol, cis-geraniol, and trans-geraniol are all alcohols which appeared in mass spectra in 13, 12, and 11 samples, respectively, out of 15 total Rosa palustris samples. The ester, geraniol acetate, which is described as having a “floral or fruity” rose aroma (Chemicalland21.com, 2010), appeared in mass spectra in ten out of 15 R. palustris samples. (R)-alpha pinene, which is a bridged hydrocarbon, appeared in all 15 R. palustris samples and is also described as a volatile rose compound. For Rosa palustris var. scandens, the alcohols phenylethyl alcohol and cis-geraniol appeared in the mass spectrum obtained. Also present were the aldehyde nonanal, which is described as having a strong “floral or fruity” aroma, and (R)-alpha-pinene. Combined, our work represents the first known analysis of the volatile organic fragrance compounds found in R. palustris and R. palustris var. scandens.• Future research will allow us to correlate each rose with its pollinators and to examine how fragrance signatures affect insect visitors’ responses to the scents produced.
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