Each flower emits a distinct profile of scents to attract pollinators or protect themselves from herbivore and pathogen attacks. Floral scents constitute a complex blend of volatile organic compounds (VOCs) synthesized in the cytoplasm of petals and released at specific time periods. As of now, there is little knowledge on the transport mechanism of floral scents, thought to be affected by protein synthesis and the activity of membrane transport proteins as VOCs move through the cell wall and cuticle layer. However, more research is needed to gain insights into the ecological evolution of plants in relation to their interaction with various organisms such as pollinators or herbivores. 

In an interview with The KAIST Herald, Professor Hyoungsoo Kim from the Department of Mechanical Engineering and Professor Sang-Gyu Kim from the Department of Biological Sciences discussed their work titled “Real-time Visualization of Scent Accumulation Reveals the Frequency of Floral Scent Emissions” published in Frontiers in Plant Science on April 18. In the paper, they measured the accumulation and the emission frequency of linalool, a main component of VOCs from lilies, by using its differences in the refractive index compared to ambient air. 

Could you briefly explain your scientific paper to our readers?

In this paper, we tried to answer the following question: Do flowers emit floral volatiles continuously? We designed a new instrument to measure the [emission of] floral volatiles in real-time and found that lillies emit floral volatiles discontinuously.

What initially inspired your team to conduct the research?

This project started from an unintended meeting. Professor Hyoungsoo Kim from the Department of Mechanical Engineering and Professor Sang-Gyu Kim from the Department of Biological Sciences met at the welcome meeting for new faculty members at KAIST. In the meeting, each faculty member introduced [their current area of research] and what they want to do at KAIST. During this conversation, Professor Sang-Gyu Kim, a plant scientist, found that Professor Hyungsoo Kim, an engineering scientist, has a great interest in nature and is able to visualize unobservable volatile compounds [from flowers]. In brief, this project started out as fun.

How does your research differ from previous works analyzing floral volatile organic compounds?

Previous works have focused on the identification or quantification of floral volatiles. In this project, however, we developed a method to measure the emission frequency of floral volatiles in real-time. Also, we could see the accumulation of the floral scents directly through laser interferometry.

Could you explain how the laser interferometer was used to visualize scent emissions and how Fourier transforms were used for data processing? 

The laser interferometer is used to measure the relative speed of light in different media. For example, water and air have different refractive indices [of 1.333 and 1.000, respectively]. Different gases can have different refractive indices depending on their molecular structures. The larger the refractive index [of a medium], the slower the light travels. To detect the difference in refractive indices of floral scents, we specifically used the Mach-Zehnder Interferometry method. The obtained experimental results have a certain fringe pattern. If there are some differences in the refractive index, [for example, if] some other volatile vapors exist in the air, a different fringe pattern is shown. Fast Fourier transform (FFT) is the conventional way to analyze the fringe pattern quantitatively.

What are the likely biological factors or mechanisms that lead to the discontinuous emission of VOCs in lilies?

This is a really hard question. We know little about how flowers emit volatiles. There are several hypotheses that explain the discontinuous emission. The biosynthesis of floral volatiles may not be a continuous process, causing certain levels of floral volatiles to be required for the penetration of chemicals through the cell wall of petals.

How did your research benefit from contributions from both the Department of Mechanical Engineering and Department of Biological Sciences?

This work could only be done through the collaboration between the natural and engineering sciences. Also, a conventional technique in a specific area was applied to explore a scientific question that has never been discussed before.

Do you have any follow-up studies you intend to conduct in the future?

Currently, we are discussing several points: [Firstly, whether we can] increase or improve the measurement sensitivity and accuracy to investigate another flower — [for instance, a more genetically simple flower — and [whether we can] also conduct 3D measurements for floral scents; however, this idea is somewhat crazy at the moment.