As a result of global warming, crops such as barley not only have to contend with increasing drought, but also with infestation by fungi, which multiply particularly well in warm conditions. However, plants have a kind of immune system consisting of many different active substances to defend themselves against such pathogens. Researchers at the Leibniz Institute of Plant Biochemistry (IPB) in Halle (Saale) and the University of Cologne have investigated in detail what this defence system looks like in barley and where its limits lie.

The immune system of plants

We know from studies on cultivated plants that plants are not defenceless against pathogens such as fungi, but defend themselves against the intruders with a cocktail of different active substances that keep the growth and reproduction of the pathogens in check. The plant defences of this immune system are known as phytoalexins, the composition of which is unique to each plant species. However, it has not yet been fully clarified which groups of substances play a role in the various cultivated plants and what exactly they do to the pathogens.

In their study on barley plants (Hordeum vulgare), the research team has now discovered that barley produces a type of phytoalexin in its roots that is effective against a very broad spectrum of fungi. The researchers named this newly discovered group of substances Hordedane, derived from the Latin name of barley. They were able to identify a total of 17 different hordedanes in barley. They also succeeded in deciphering the metabolic pathway by which they are produced. The researchers recently published the results of their study in Molecular Plant.

No one hundred per cent protection

In their study, however, the researchers were surprised to discover an exception: Bipolaris sorokiniana, a root rot pathogen. Not only was the fungus unimpressed by the hordedans, but it even grew better in the presence of these phytoalexins, which were originally produced to repel it.

Bipolaris, which is particularly widespread in warm regions but is gradually migrating northwards, therefore uses theHordedans to its own advantage. According to the study, the fungus transforms the plant defence substances into fungal structures and uses them to keep the root cells of the barley infected by the fungus alive for longer. This gives the fungus more time to grow and strengthen itself before it attacks other plants by forming spores. How exactly Bipolaris manages this trick is still largely unclear.

am