Queen of the night opens its large white flowers at night, only for them to wilt the following morning. During that brief bloom, how do the compounds entering the air change, and how are they made inside the flower? One study examined overnight changes in these compounds and the mechanism producing the major component geraniol.
In a study published in February 2025, researchers collected compounds emitted by queen of the night every hour from evening until the next morning. Alongside increases and decreases in the amount released, they found changes in the composition over the course of the night. The species studied was Epiphyllum oxypetalum, a member of the cactus family known in Japanese as gekkabijin.
Collecting the Air Around a Flower Every Hour
The team studied queen of the night plants cultivated in Sichuan Province, China. They enclosed each flower in a bag and supplied purified air, capturing compounds in the outgoing air on an adsorbent. Unlike soaking a flower in solvent to extract its components, this measurement tracks what enters the air from a blooming flower.
Samples were taken at 13 time points, from 7 p.m. to 7 a.m. the following morning, local time. Three flowers on different plants were measured simultaneously. Empty bags were also measured so that compounds originating from the bags or apparatus could be subtracted.
The collected compounds were analyzed by GC–MS, a method that separates a mixture and investigates the identity of its components. The study reported 49 volatile organic compounds, or VOCs. However, not all were matched against reference standards; the list also includes tentative identifications based on database comparisons.
The Composition Changes as the Night Progresses
The total measured VOC emission followed a single-peaked pattern, increasing markedly during the night and then declining. The paper identifies the 2 a.m. sampling stage as the maximum. The most abundant compounds at that time were geraniol, benzyl alcohol, and methyl salicylate.
Geraniol is a molecule known for its rose-like scent and is also used in perfumery. In this study, it was the most abundant of the detected compounds at the peak-emission stage. It is an important clue when investigating the scent of queen of the night.
Its proportion was not the same throughout flowering, however. Early in the bloom, a group of compounds called benzenoid esters accounted for a high proportion; later, terpenoids such as geraniol predominated. As the flower wilted, the proportion of esters increased again.
The distinction to make here is between amount and proportion. An increase in a compound’s proportion does not necessarily mean that its emission has increased. Its share of the total can also grow because other compounds decrease. The dawn results cannot be reinterpreted as showing that “the ester scent becomes stronger and stronger.”
Individual compounds did not all change in the same way either. Geraniol and benzyl alcohol each showed a single emission peak, whereas methyl salicylate showed two. The flower was not simply increasing and decreasing a fixed mixture of compounds as a whole.
Measured Amounts and the Scent We Perceive
These results show that the mixture of compounds emitted by queen of the night changes over one night. However, this was not a study in which participants smelled the flowers and rated the time of greatest perceived intensity or the way the scent’s character changed.
The count of 49 compounds does not mean 49 odors that people can distinguish. Nor does geraniol’s predominance alone justify describing the whole flower as smelling “almost like a rose.” The whole-flower chemical analysis described so far examined how the mixture underlying scent perception changes with time. The study went on to explore how those compounds are made.
Inside the Flower: How Scent Is Made
The researchers also investigated which parts of the flower emit the compounds. Comparing petals, sepals, floral tubes, stamens, and pistils, they detected geraniol and benzyl alcohol mainly from petals and sepals. This comparison used a different method in which collected tissues were heated to collect the compounds, so its conditions differed from the overnight whole-flower measurements.
They also investigated candidate enzymes for producing geraniol, and experiments with purified enzyme confirmed that an enzyme called EoTPSa1 could produce geraniol from a precursor molecule. Chemically inhibiting the mevalonate pathway, which supplies precursors, also greatly reduced geraniol emission.
In an experiment using a fluorescently tagged enzyme expressed in the leaves of a tobacco relative, they also confirmed that the enzyme was present in the cytosol rather than transported into chloroplasts. Together with the precursor-supply experiments, this suggests that cytosolic geraniol synthesis is important in queen of the night. Plant monoterpenes are generally made in plastids such as chloroplasts using precursors supplied by a different pathway. The important finding here was the demonstration in queen of the night of a route linking the cytosolic mevalonate pathway to a terpene synthase, showing the diversity of mechanisms that can produce the same geraniol molecule.
These findings support a mechanism for geraniol production inside the flower. They do not, however, show that this one enzyme determines all the overnight changes in scent. To understand the temporal pattern of each compound, we need to consider not only what can be produced but also when, how much, and when it is released.
Summary
Understanding the scent of queen of the night requires looking both at what is emitted when and at how it is made inside the flower. This study captured overnight changes in the compounds while showing a mechanism by which the major component geraniol is produced through the cytosolic enzyme EoTPSa1 and precursors supplied by the mevalonate pathway. An important contribution lies in connecting floral scent from the perspectives of both emitted compounds and biosynthesis.
If we bring these findings into perfumery or scent documentation, one possible idea is to record not only “queen of the night scent” but also which stage of flowering was captured. This is not a documentation method whose effectiveness was tested in the paper, but a practical idea informed by the time-dependent changes in composition. Its relationship to human impressions still needs separate investigation, yet there is something intriguing about paying attention to which part of the same flower’s single night we are observing.
Original Study
Yiyang Zhang, Yuhan Zhang, Andong Zhang et al.
Floral scent emission of Epiphyllum oxypetalum: discovery of its cytosol-localized geraniol biosynthesis
Horticulture Research 12(5), uhaf039 (2025).
First published: February 11, 2025. Publisher’s “Corrected and typeset” date: May 1, 2025.
DOI: https://doi.org/10.1093/hr/uhaf039
Full text: https://academic.oup.com/hr/article/12/5/uhaf039/8008354
Original study license: CC BY 4.0
https://creativecommons.org/licenses/by/4.0/
The original Japanese article is an independently structured explanation based on the study. It does not reproduce a translation of the paper or its figures and tables. The authors declared no competing interests.
Verification of the Japanese and scientific names: Tokyo Metropolitan Park Association, “Gekkabijin (Queen of the Night)”
https://www.tokyo-park.or.jp/park/hachijo/flora/detail/029.html
