Plant Drought Response Hormone Found to Block Spider Mites

Recent findings that plants employ a drought-survival mechanism to also defend against nutrient-sucking pests could inform future crop breeding programs aimed at achieving better broadscale pest control.

Using an advanced fluorescent biosensor (ABACUS2) that can detect tiny changes in plant hormone concentrations at the cellular scale, scientists saw that abscisic acid (ABA), usually linked with drought response, started closing the plant’s entry gates within five hours of being infested with spider mites.

Microscopic leaf pores (stomata) are important for gas exchange but are also the major sites for water loss. When there is a water shortage, plants act to conserve water by producing the drought stress hormone ABA to close their stomata.

Coincidentally, the closure of stomata also obstructs the preferred entry points for nutrient-sucking pests like spider mites. The two-spotted spider mite is one of the most economically damaging pests — it’s not fussy and attacks a broad range of more than 1,000 plants, including 150 crops. Barely visible to the naked eye, these tiny pests pierce and then suck dry plant cells. They can build up to enormous numbers very quickly and can be one of the most destructive pests in the garden and horticulture industry, spoiling house plants and reducing yields of vegetables, fruit, and salad crops.

There has been debate about ABA’s role in pest resistance. Initially, it was noticed that stomata close when plants are attacked by nutrient-sucking pests, leading to various hypotheses, including that this closure could be a plant response to losing water due to the pests’ feeding or even that the pests act to close stomata to prevent plants from sending distress volatiles to pest predators.

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In a collaboration between the Centre for Plant Biotechnology and Genomics (CBGP) in Spain and Sainsbury Laboratory Cambridge University (SLCU), researchers studying how thale cress (Arabidopsis thaliana) responds to the two-spotted spider mite (Tetranychus urticae) have determined the plant leaps into action almost immediately, employing the same hormone as for drought to also block spider mites from penetrating plant tissues and, as a result, significantly reducing pest damage.

The findings published in Plant Physiology found the peak closure of stomata is achieved within a time frame of 24 to 30 hours.

“Open stomata are natural apertures where pests like aphids and mites insert their specialized feeding structures, called stylets, to pierce and then suck out the nutrient-rich contents from individual sub-epidermal cells,” says Irene Rosa-Díaz, who carried out the spider mite experiments at SLCU and CBGP during her PhD with Professor Isabel Diaz at the Centro de Biotecnología y Genómica de Plantas, Universidad Polytécnica de Madrid, and National Institute of Agricultural and Food Research and Technology (UPM-INIA).

For more information, please continue reading the original release at Sainsbury Laboratory’s section on the University of Cambridge website.

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