Do Rose Petals and Stamens Give Off the Same Scent?

When you think of rose fragrance, you may picture petals. But within a single flower, do petals, stamens, and pistils produce the same compounds?

In 2024, Lijun Zhou and colleagues studied Rosa gigantea, a wild species ancestral to tea roses. They investigated its characteristic tea scent through the locations and times at which compounds occur and through gene activity. Conserving wild genetic resources and using them to breed roses with diverse fragrances were also major goals.

Comparing a tea-scented wild rose across locations and times

Tea scent is a name for the fragrance of roses of Chinese origin, likening their faintly medicinal impression and refreshing sweetness to tea. This study used Rosa gigantea grown in a garden in Kunming, China, and the China rose “Old Blush” for comparison.

For Rosa gigantea, the researchers compared six tissues: petals, stamens, pistils, sepals, the receptacle supporting the flower, and leaves. They also examined five stages from young buds to fully open flowers and six times of day: midnight, 4 a.m., 8 a.m., noon, 4 p.m., and 8 p.m. Biological replicates from three individuals were used for each sample type.

Scent compounds were separated and examined using gas chromatography–mass spectrometry. An important detail is that the chemical analysis used frozen, ground samples, with compounds collected from the gas inside a container at 100°C for 15 minutes. These were not measurements of air emitted directly by flowers in the field.

A separate sensory evaluation involved 18 participants. After odor-discrimination checks and training, they compared the fragrance with seven representative rose cultivars and rated scent intensity at different flowering stages on a scale of 0–5. This evaluation used fresh flowers. Human-perceived intensity and amounts detected from heated samples need to be treated as separate kinds of information.

Different compounds stood out in stamens and pistils

The analysis selected 48 scent-related compounds for comparison. Petals, stamens, and pistils were strongly scented in the sensory evaluation, but their constituent profiles in the chemical analysis differed among tissues.

Eugenol and structurally related compounds were particularly distinctive. Eugenol was abundant in stamens; the paper reports amounts 20–100 times those in other tissues. In contrast, isoeugenol was abundant in petals and methyl eugenol in pistils, and these two were not detected in stamens.

Even structurally similar compounds were abundant in different locations within the flower. Some compounds were detected only in leaves, while others were characteristic of green tissues such as sepals. Combining all flower constituents into a single profile makes these differences harder to see.

The 20–100-fold figure here compares compound amounts obtained under standardized analytical conditions. It does not mean that smelling stamens produces a sensation 20–100 times stronger than smelling petals.

Spatial differences within petals as well

The researchers also stained floral tissues with a dye and examined cells by electron microscopy. In petals, the base near the central reproductive organs stained strongly and had more densely arranged cells than the edges or middle. Surface-cell shapes also differed between the front and back sides.

The authors use these structures and staining patterns as clues to scent distribution within flowers. However, dye intensity is not a direct quantitative measurement of scent emitted from a location. Nor was cell shape alone proven to determine emission amounts.

The authors discuss the possibility that these spatial differences act as guides directing insects toward the flower’s center. If stamens and pistils are rich in different compounds, they might provide positional information to pollen-carrying insects.

However, no experiment removed particular compounds or offered insects a choice to verify this mechanism in Rosa gigantea. An insect-attracting function is a hypothesis based on compound distributions and previous research.

Changes with flower opening and time of day

Across flowering stages, scent intensity and major volatile compounds in Rosa gigantea tended to increase from young buds to the beginning of opening, then decline from half-open to fully open flowers. A more fully open flower was therefore not necessarily more strongly scented.

During observations across a day, bees visited more often during the period of flower opening and strong scent from around 8 a.m. to noon. Many compounds were detected at multiple time points, but their amounts changed.

However, the flowers were also progressing through opening during that day. The experiment did not fully separate time-of-day effects from developmental-stage effects or isolate the internal clock under constant conditions. The results cannot be generalized to conclude that all roses smell strongest at the same time.

Exploring scent mechanisms through a wild rose’s genetic information

The study also decoded the genome, the complete genetic information, of Rosa gigantea. The researchers assembled sequences corresponding to seven chromosomes without the gaps present in previous rose genomes. Comparisons with other roses revealed gene groups characteristic of this species and large sequence differences.

In particular, gene groups associated with scent-compound biosynthetic pathways had expanded, which the authors regard as one factor underlying the distinctive tea scent. They also measured RNA to examine how much genes were used in each tissue and at each time, comparing this with changes in compound amounts.

The candidate genes active when eugenol was abundant in stamens differed from those active when methyl eugenol was abundant in pistils. The researchers also inferred regulatory connections while considering time lags in which scent-related gene activity changed before compound amounts did.

Many of these relationships are predictions built from corresponding increases and decreases in genes and compounds or from DNA sequences. The researchers did not experimentally confirm every instance of one gene directly controlling another or causing a compound to increase.

Cell-based experiments for some genes

Some combinations, however, were tested experimentally rather than remaining predictions. The researchers examined whether a candidate regulator, RgMYB091-like1, acts on the region that initiates expression of RgOOMT1, a candidate gene associated with scent-compound biosynthesis.

In an experiment using Arabidopsis cells and luminescence to measure gene expression, adding this regulator increased the signal. This supports promotion of gene expression by that combination. However, the study did not change the gene in rose flowers and demonstrate a subsequent change in scent compounds or human-perceived fragrance.

Sequence comparisons, patterns of simultaneous change, and tests of activity in cells each have their own evidential scope. The study combined these approaches to narrow down mechanisms for further investigation.

Conserving wild diversity to expand fragrance possibilities

The authors connect this work to breeding and conservation because wild species retain genetic differences that cannot be captured by studying cultivated roses alone. Using only one cultivar’s genome as a reference may overlook distinctive genes or regulatory differences in another species.

Assembling information across tissues, times, and flowering stages in Rosa gigantea provides a foundation for recording its genetic resources and using them in scent breeding. The authors discuss new domestication approaches that exploit wild-species characteristics and the possibility of combining selection with genomic technologies. The study did not already produce roses with new fragrances.

The research was supported by China’s Fundamental Research Funds for the Central Universities, National Key Research and Development Program, and National Natural Science Foundation. The authors declared no competing interests.

Summary

In Rosa gigantea, the scent compounds abundant in petals, stamens, and pistils differed, while compounds and gene activity also changed across flowering stages and within a day. The fragrance of a single flower can thus be understood as a phenomenon with spatial and temporal variation.

The study’s importance lies not only in documenting these differences but also in linking them to a wild rose’s genetic information. It placed hypotheses about positional cues for insects and candidate regulators of scent production in a form that can be tested in subsequent experiments. The authors’ broader proposal is that conserving wild-species diversity also provides a foundation for expanding the range of rose fragrances available in the future.

References

Zhou, L., Wu, S., Chen, Y., et al. (2024). Multi-omics analyzes of Rosa gigantea illuminate tea scent biosynthesis and release mechanisms. Nature Communications, 15, 8469. DOI: 10.1038/s41467-024-52782-9. Full original article. © The Author(s) 2024. The original article is licensed under CC BY-NC-ND 4.0.