A team of researchers at the University of Szeged (SZTE) has identified a previously unknown element in plant defence mechanisms that could boost resistance to harmful pathogens. The study, led by Zalán Czékus and Péter Poór from the university’s Department of Plant Biology, was recently published in Physiologia Plantarum, a top-tier scientific journal in the field.
Plants, when under attack by pathogens like bacteria, are known to rapidly close their stomata—the small pores on their leaves—to prevent invaders from entering. This reaction has been understood since 2010 to be largely driven by the hormone ethylene, which triggers this closure within an hour of detecting a microbial threat.
But SZTE’s researchers went further. They found that, beyond simply closing these pores, the guard cells responsible for this action also produce a defensive protein called defensin. The production of this protein is linked to a later-stage response involving another hormone, jasmonic acid, which activates roughly six hours after the initial attack. This dual-phase response was previously unrecognized in detail.
To pinpoint where defensins appear in the plant tissue, the team generated antibodies and tracked them with gold-tagged markers under an electron microscope. They found a significant accumulation of defensins in the outer epidermis and in the guard cells—exactly where bacteria attempt to breach the plant’s surface.
Using PCR testing, the scientists confirmed that not only the leaf’s internal mesophyll cells but also the guard cells themselves produce defensins. Previous work by Czékus had already shown that plant immune responses can extend beyond the infected area, affecting upper layers of the foliage.
The study also included advanced photosynthesis measurements, rarely available in Europe, to observe how the immune response impacts plant energy production. It showed that while photosynthesis temporarily declined in the guard cells after treatment, the overall photosynthetic function of the plant remained stable—a sign that the plant reallocates its resources during defence.
Currently, researchers at SZTE’s Department of Biotechnology and Microbiology are testing tomato-derived defensins against a variety of plant pathogens. The long-term goal is to use these naturally occurring compounds—possibly in the form of protective sprays—to enhance crop resistance in an environmentally friendly way.
This discovery not only deepens our understanding of plant immunity but also opens practical avenues for more sustainable agriculture using the plants’ own biochemical defences.
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