A Sunflower's Scent

As plants live within different environments, they will encounter different pressures and stresses. One of the ways that plants deal with these pressures and stresses is by producing volatile compounds. Volatile compounds are organic compounds that evaporate quickly when exposed to air. This is an important feature that allows these compounds to carry a message to neighboring organisms. Volatile compounds can help increase a plant's chance of survival in several ways. 

Benefits of Volatile Compounds:

(1) Attract pollinators, seed dispersers, or organisms to form beneficial interactions with 

(2) Repel diseases and insects

(3) Decrease competition with neighboring plants 

(4) Increase ability to survive drought, heat, etc.

Terpenes are among the most common and important volatile compounds in plants. For most plants, they are what you can smell from a plant’s fruit, flower, and leaves. There are more than 25,000 types of terpenes produced by plants. Some of the most common classes of terpenes are monoterpenes and sesquiterpenes. Monoterpenes are known to be involved in attracting pollinators. Sesquiterpenes are known to be involved in fighting off pests and diseases.

Given its high level of genetic diversity and ease of growing, sunflowers are one of the best plants for agricultural studies. Commercial sunflowers are susceptible to many environmental stresses. On the other hand, wild sunflowers are very resilient and can grow in harsh environments. Compared to commercial sunflowers, wild sunflowers have stronger scents. Since volatile compounds make up the plant’s scents, we suspect they have something to do with the resilience. Unfortunately, there is not much information available about volatile compounds in wild or commercial sunflowers. A better understanding of the relationship between sunflowers’ volatile compounds and their roles in plant resilience may enable plant breeders to develop more resilient sunflowers.

Each year, farmers spend lots of time and money trying to protect their sunflowers from environmental stresses. At the same time, climate change is making these stresses worse year by year. In addition, the large amounts of pesticides being used by farmers to protect their sunflowers are polluting our food and environment. If scientists could manipulate volatile compounds in sunflowers in order to develop resilient plants, the plants could defend themselves to a higher degree without farmers interfering. This could lead to safer, cheaper food, and reduce the expenses associated with protecting the plants. 

We wanted to investigate any relationship between volatile compounds and resilience in sunflowers. In order to investigate this relationship, we first needed to identify the volatile compounds present in sunflower varieties. To do this, our first step was to use gas chromatography (a technique to observe volatile compounds) to see what volatile compounds are present in different parts of wild sunflowers. Specifically, we aimed to investigate the volatile compounds in the leaves and petals of different wild sunflowers.

In our greenhouse, we grew 40 types of wild sunflowers. Then, we took samples of leaves and petals from the healthy plants and analyzed them for their volatile compounds. 

Across the 40 wild sunflower types, 500 volatile compounds were identified. 61% of these identified compounds were terpenes: 40% sesquiterpenes and 18% monoterpenes. This emphasizes the importance of terpenes and their possible contributions to plant survival. 

The results showed that the 40 types of wild sunflowers have significantly different makeups of volatile compounds. For instance, the leaves could have anywhere from 9% to 93% of sesquiterpenes. This demonstrates the variety in terpene production and allows scientists to study the genetics underlying this diversity. On average, leaves had more volatile compounds (mostly sesquiterpenes). On the other hand, petals had less volatile compounds (mostly monoterpenes).

Among the 40 types of wild sunflowers, the makeup of volatile compounds in leaves and petals were independent from each other. It is important to note that the independence of volatile compound profiles in leaf and petal implies that leaves can evolve independently from petals. This makes it possible for scientists to manipulate terpene makeup in leaves without worrying about unintentional changes in petal terpenes. It would be interesting to continue to look into this diversity and potentially manipulate the volatile compound makeup in sunflowers.

However, we found that volatile compound makeup depended on what climate the wild sunflowers came from. For instance, if the wild sunflowers came from drier climates, they had leaf compositions with a higher proportion of total monoterpenes (terpene involved in attracting pollinators). This might be due to the reason that growth seasons in dry climates are usually short. To make the most out of it, plants evolutionarily have tried to produce more monoterpenes to be able to attract more pollinators and set more seeds for their next generation. On the other hand, those from more humid habitats contained a higher proportion of total sesquiterpenes (terpene involved in repelling diseases and pests). This might be due to the fact that pests and diseases in humid climates are usually more common. Therefore, plants evolutionarily have been forced to produce more sesquiterpenes to cope with the pest and disease pressure.  

Our main goal in this big and long-term sunflower project is to understand the relationships between volatile compounds and resilience in sunflowers. As the first step in this project, we generated the first dataset characterizing the makeup of volatile compounds in the leaves and petals of wild sunflowers. In future studies, we aim to build on these findings and study the volatile compounds in commercial sunflowers to see how they are different from those in wild sunflowers. It would then be important to test these wild and commercial sunflowers against different pressures such as drought and disease to investigate their resilience. It would also be beneficial to study volatile compounds in other parts of the sunflowers, such as the roots. 

Together, these studies may help plant breeders develop more resilient sunflower varieties that can survive better in order to grow food at a lower cost, reduce the cost associated with growing plants, and enable plant breeders to develop more resilient sunflowers. In addition to this, it helps scientists have a better understanding of plant-environment interaction.   

Written By: Keivan Bahmani

Academic Editor: Biologist

Non-Academic Editor: High Schooler

Original Paper

• Title: Broad diversity in monoterpene–sesquiterpene balance across wild sunflowers: Implications of leaf and floral volatiles for biotic interactions

• Journal: American Journal of Botany

• Date Published: 01 November 2022

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