You Can Smell Plants, But Can They Smell You?

The vast majority of aromas and flavours you have come to know and love originate from plants! The spicy scent of cinnamon bark, sharp bite of a basil leaf, or the soft aroma of a rose. Plants often release fragrant chemicals into the air, called volatile organic compounds. These are the same chemicals humans may find appealing and herbivores may be averted to. The cocktail of chemicals released by the plant depends highly on the species and response to interactions, for example, herbivory or pollination. Plants use these chemicals to prompt a physiological response, typically via gene expression, from the initial signal that was sensed. Essentially, one part of a plant facing herbivory may use volatile organic compounds to signal a herbivory response in nearby parts of the plant! As a result, the ability to smell, or detect volatile compounds, helps a plant fight attack.

Given that plants can smell themselves, could they possibly smell other plants as well? Yes! Plants can eavesdrop on their neighbours! If the neighbouring plant is close enough to detect the volatiles, their cellular receptors use the same mechanisms of detection as would be used for volatiles of the same plant thus eliciting the expected response. Furthermore, there is evidence that plants can detect compounds of species other than their own! The most compelling evidence of plant eavesdropping is from a study aimed to assess the response of plants in response to herbivory in a neighbouring plant. As hypothesized, they showed that the defense chemicals produced by the infested plants triggered a response in the neighboring plants. As a result, the chemicals elicited an anti-herbivore response in the neighbouring plants prior to herbivore arrival thus reducing herbivore damage when infestation did occur. By chemically eavesdropping on their neighbors, they could respond and allocate resources to ramp up their own defenses, giving them a competitive advantage. Studies of these kinds have led to hypotheses that these signal chemicals can be utilized in an agricultural setting. One such possibility is to spray crops with the appropriate cocktail of volatile compounds that signals to the plant to protect itself from pests before they are attacked, potentially preventing major crop losses. Unfortunately, many of these compounds serve multiple functions and involve the interaction of several genes. The interaction between these chemicals remains largely understudied and subject to future research.

The distinction between “smell” and “taste” arises from the difference in if the compound is dissolved or volatile. While these two senses are intimately related, they may lead to differing responses. Many dissolved compounds have a volatile form. For example, the jasmonic acid is a dissolved compound with its volatile counterpart being methyl jasmonate. In some instances, these chemicals elicit similar responses while in others, the response is slightly different.

Furthermore, the exact mechanism by which plants ‘smell’ and ‘taste’ remains understudied. Plant responses to herbivore and pathogen attack are well know