Plants Emit Isoprene, a Volatile Organic Compound (VOC) That Repels Insects: Three Papers Show How It Protects Plants, Its Oxidation Chemistry and Environmental Impacts, and How Its Production is Triggered in Soybeans

     

     Scientists at Michigan State University, detailed by Interesting Engineering, have recently (April 2025) solved a mystery about isoprene, a volatile organic chemical (VOC) released naturally by some plants. Its chemical formula is C5H8. Isoprene is the second most abundant hydrocarbon being emitted to the atmosphere after methane. It interacts with sunlight and nitrogen oxides from vehicle exhaust and industrial emissions, contributing to the formation of ozone, aerosols, and other pollutants that degrade air quality. The researchers wanted to know why only certain plants produce isoprene. They compared isoprene-emitting (IE) plants to plants that don’t emit isoprene (NE). They found that isoprene emission helps with heat stress and with deterring insects. The researchers grew two types of tobacco plants. One was genetically altered to produce isoprene, and the other was not. The plant not altered was invaded by whiteflies, but the one that produced isoprene was not. The same was done with hornworms. It was found that the isoprene did not deter them directly but indirectly by increasing the plant’s production of jasmonic acid, a defense hormone that disrupts an insect’s ability to digest protein.

“Another surprise came from soybeans. Long believed to have lost the ability to make isoprene through evolution, soybeans were found to release it in small bursts when their leaves were damaged. The discovery suggests they still carry the gene to produce isoprene and switch it only under stress.”

     The first paper, published in Science Advances, details how isoprene deters insects.

     The figure below from the paper clearly shows the damage to non-emitting (NE) plants only.

     While crop plants generally don’t emit isoprene, June 2025 research from scientists at the University of Illinois shows that soybeans do emit it when their leaves are wounded or during high temperatures. However, they make isoprene at much lower rates than typical isoprene-emitting plants. Also, it was reported in the paper that:

“Isoprene emission in soybeans was linked to reduced photosynthesis rates and stomatal conductance.”

     Just this morning, I was checking my edamame soybeans that have just sprouted or are in the process of sprouting. Unfortunately, a raccoon has been digging around and breaking the sprouts. I’ll probably lose quite a bit of them, unfortunately. The sprouting plants seem to be very brittle and vulnerable to being snapped below their cotyledons (the leaves that feed them until they are established), which means they won’t re-sprout. If only the isoprene could deter raccoons!

     The paper also noted that wounding-induced isoprene emission showed a connection with elevated jasmonic acid, as in the Michigan State study. The movie below shows the lab setup for the analysis in action, with the bell curve on the left presumably showing the emission of isoprene after the leaf was damaged.

     A February 2026 paper in the Journal Atmosphere explored isoprene emissions, their oxidation chemistry, and their environmental impacts. The paper notes that isoprene emissions affect the oxidizing capacity of the atmosphere. As the paper’s abstract notes, isoprene emissions are strongest in tropical regions:

“The emission of isoprene is strongest in tropical forested regions, suggesting a major portion of tropospheric chemistry occurs in the tropics. As well as deforestation and reforestation having a direct impact on the world’s climate through land cover, there is also an indirect environmental impact (e.g., global warming, air pollution) through the resulting change in isoprene emissions.”

     The paper notes that 90% of non-methane volatile organic compounds (VOCs) emissions come from terrestrial vegetation. Among biogenic VOCs, isoprene emissions dominate. The table below shows that broadleaf tropical evergreen trees dominate isoprene emissions, followed distantly by broadleaf deciduous temperate trees. The Amazon appears to be the world’s hotspot for isoprene emissions.

     The researchers discovered why previous models of isoprene emissions did not match the far greater levels of HOx radicals that were measured over pristine Amazon rainforests than predicted. They revised the oxidation chemistry to include the isomerization reactions that were discovered following the initial oxidation of the HOx radicals. As the paper’s conclusions below recount, there are several variables that affect isoprene emissions, including temperature, water availability, light, season, and time of day. Uncertainties in quantifying isoprene emissions remain, despite the important discoveries made in the paper.

 

References:

 

Plants emit insect-repelling chemical that could secretly be poisoning our air.  Neetika Walter. Interesting Engineering. June 19, 2025. Plants emit insect-repelling chemical that could secretly be poisoning our air

Cryptic isoprene emission of soybeans. Mohammad Golam Mostofa, Abira Sahu, Yuan Xu, +3 , and Thomas D. Sharkey. PNAS. Vol. 122 | No. 24. June 12, 2025. Cryptic isoprene emission of soybeans | PNAS

Isoprene deters insect herbivory by priming plant hormone responses. Abira Sahu, Mohammad Golam Mostofa, Yuan Xu, Bianca M. Serda, James O’Keefe, and Thomas D. Sharkey. Science Advances. 18 Apr 2025. Vol 11, Issue 16. Isoprene deters insect herbivory by priming plant hormone responses | Science Advances

Isoprene Emissions, Oxidation Chemistry and Environmental Impacts. M. Anwar H. Khan,Rayne Holland, Charlotte Mould, Asan Bacak, Carl J. Percival, and Dudley E. Shallcross. Atmosphere. Volume 16. Issue 3. February 24, 2026.  Isoprene Emissions, Oxidation Chemistry and Environmental Impacts