How a perfume opened doors to plant research – 12/15/2023 – Fundamental Science

In the early 1960s, the perfume industry was faced with one of its most coveted enigmas: the chemistry of the scent of jasmine. The chemical identity of the sweet essence of the jasmine flower was a coveted treasure, a kind of Holy Grail of aromas, rivaled only by the perfume of roses. If the secret was revealed, that much appreciated and striking fragrance could be synthesized on an industrial scale, eliminating the need for a costly and ineffective process highly dependent on flowers.

Using cutting-edge techniques at the time, a group of French chemists led by the Swiss Édouard Demole identified, in 1962, the main constituent of jasmine odor, a volatile compound of lipid nature called “methyl jasmonate”. In addition to solving the mystery behind that perfume, the chemical structure of this molecule also revealed a curiosity: an incredible similarity to prostaglandins, a group of hormones that modulate the immune system in animals.

While for the perfume industry Demole’s work represented the end of a mystery, for botany he opened the doors to another enigma. The chemical identity of methyl jasmonate allowed several research groups around the world to note that the production of this compound and analogous molecules (called jasmonates) was not restricted to jasmine, but was synthesized by all land plants.

These studies also demonstrated that jasmonates had curious biological properties, acting, for example, as potent growth inhibitors and aging modulators in plants. Such observations served as a starting point for an idea that began to take hold in the 1980s: jasmonates were more than just perfumes. Their scope throughout the plant kingdom suggested an important and vital function of these molecules. But which would it be?

The watershed in the history of jasmonates was the American biologist Clarence Ryan. Researcher at Washington State University (USA), Ryan focused his studies on the interaction between plants and insects, investigating an interesting phenomenon present in tomato plants eaten by beetles. When attacked, tomato plants produced and accumulated a large amount of proteinase inhibitors, a group of proteins that make the leaf less palatable and more difficult for insects to digest. This scenario can be understood as a plant defense mechanism, since the nutritional value of the green tissue is reduced, often leading to the beetles dying from starvation if they do not switch hosts.

In the mid-1990s, when setting up a standard herbivory experiment, Ryan made a serendipitous observation: while tomato plants attacked by beetles produced proteinase inhibitors (as expected), insect-free plants, but close to those that were herbivorous, also activated defense mechanisms. In other words, he noticed a form of communication between plants to activate a collective response against enemies. In a short time, his research group arrived at a volatile compound emitted by herbivorous plants that served as an indicator of danger for other plants: the already known methyl jasmonate.

Clarence Ryan’s observation was the starting point for a series of scientific research that took jasmonates to a new level. If in the 1960s they were seen as mere constituents of floral perfumes, today they appear as one of the most important groups of plant molecules, being described as main regulators of plant defense responses against attack by pests and pathogens. Similar to the action of prostaglandins in animals, jasmonates are regulators of the plant immune system. For plants, they are like a battle signal, promoting the production of chemical and structural defenses that aim to eliminate enemies. For insects, they are markers of the beginning of a war that could (and probably will!) cost them their lives: a scent of death.

The importance of jasmonates for plants can be observed in mutants unable to produce or perceive this group of hormones. Lacking the ability to activate defense responses, these immunosuppressed plants are completely destroyed by insects and fungi when placed in a natural environment. My laboratory has used such mutants under controlled growth conditions to identify new components of the plant immune system. Using this tool, we have noticed that the activation of defense responses is energetically costly for plants, leading to the repression of processes such as growth and flowering.

We are also trying to understand how jasmonates influence the behavior of insects, how they choose which plants to attack or not. I believe that this line of research could lead, in a short period, to the production of plants that are more resilient to attack by pests and pathogens, guaranteeing safer, more economical and much more sustainable agricultural production.

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Marcelo Lattarulo Campos is a professor of Botany at the UFMT Biosciences Institute and works with the interaction between plants and insects.

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