War isn't just for humans: In the plant kingdom, various species cooperate with each other or directly fight for resources against each other. Although it has been known for some time that plants deploy “weaponized” chemicals that target other plants they are directly competing with – and any hostile animals that are trying to consume them – a new study has revealed the specific method of attack certain plants employ. One particular class of toxin actually targets enemy plants’ genetic material in order to stunt their development, as the research, published in the journal Plant Cell, reveals.
Light, nutrients and water are all vital for a plant’s growth and survival, and the competition for them never dies down. Taller trees receive more light; deeper and more widespread roots are able to absorb more nutrients and water. The competition is undoubtedly less intense, however, if there are fewer plants competing for the same resources, and this is where chemical warfare comes into play.
Certain plants are able to produce, store and release compounds known as allelochemicals, toxic substances that manage to inhibit the growth and development of nearby plants. These chemicals are released from the roots into the soil, where they can be absorbed by nearby competitors, damaging them, perhaps fatally. Although many classes of allelochemicals have been identified over the years, the molecular-scale mechanisms behind this plant-based espionage have remained elusive, until now.
A plant produces two types of metabolites, a type of organic compound that is involved in the nutrient-to-energy conversion process within the plant. Primary metabolites are directly responsible for the plant’s survival, whereas the secondary metabolites enhance the plant’s ability to survive by allowing it to interact with its environment.
Two secondary metabolites, DIBOA and DIMBOA, are released by several grass species into the soil, which degrade into toxic chemicals harmful to other plants. The German and French team of researchers looked into the effect of these two secondary metabolites on target plant species, examining their microscopic actions.
Image credit: The metabolites are released by several grass species into the soil, where they become toxic. Juhku/Shutterstock
Plants, like animals, contain enzymes – proteins that speed up complex biological reactions. One particular type of enzyme, the histone deacetylases (HDACs), help to cause the compaction of genetic material, interfering with the process of gene expression by restricting access to bits of DNA.
The toxic chemicals that emerge from the degradation of DIBOA and DIMBOA were observed to inhibit HDACs’ ability to regulate gene expression, ultimately causing the overall growth of the target plant to slow down. Although this study only investigated the effect of these specific allelochemicals on one plant – Arabidopsis thaliana – this is the first time that the underlying molecular mechanism behind the toxicity has been revealed.
There’s more to this study than just plant-based chemical warfare. Sascha Venturelli, a medical scientist from the University of Tübingen and the lead author of the study, said in a statement: “We have found that these particular [plant toxins] efficiently inhibit the growth of human cancer cells, too.” HDACs are known to play a role in cancer development in humans; consequently, the use of HDAC inhibitors in anti-cancer treatments has been ongoing for some time. So this new research hasn’t just described how a toxin damages a target plant, but how it could potentially be used to fight against the onset of cancer in humans.