Recent research has revealed that plants utilize a drought-survival mechanism to defend against nutrient-sucking pests, such as spider mites. By utilizing an advanced fluorescent biosensor known as ABACUS2, scientists observed that abscisic acid (ABA), a hormone associated with drought response, quickly closed the stomata of plants within 5 hours of being infested with spider mites. Stomata are microscopic leaf pores essential for gas exchange but also major sites for water loss. When plants experience a water shortage, they produce ABA to close their stomata and conserve water. This closure of stomata also serves to hinder the entry of pests like spider mites, which pierce plant cells and feed on their nutrients, causing significant damage.
Spider mites, including the two-spotted variety, are destructive pests known to attack over 1000 different plants, including 150 crop species. These pests can rapidly multiply and weaken plants, impacting yields in both personal gardens and commercial agriculture. Initially, there was debate over the role of ABA in plant resistance to pests. Some hypothesized that stomatal closure in response to pest attacks was a result of water loss due to feeding, while others suggested that pests might be prompting stomatal closure to prevent distress signals from being released to attract predators. However, studies conducted by researchers at the Centre for Plant Biotechnology and Genomics in Spain and the Sainsbury Laboratory Cambridge University revealed that plants quickly respond to spider mite infestations by employing ABA to block the pests from penetrating plant tissues, thereby reducing pest damage.
The study published in Plant Physiology demonstrated that stomatal closure, induced by ABA accumulation, peaked within 24 to 30 hours after mite infestation. This response hindered the mites from effectively feeding on plant cells. The research also emphasized the importance of understanding the interactions between biotic and abiotic stresses in plants. Mite feeding triggers a series of immune signaling molecules, including jasmonic acid (JA) and salicylic acid (SA), which work together with ABA accumulation and stomatal closure as defense mechanisms against mite damage. Further investigations aim to identify the initial signals from mite feeding that trigger ABA accumulation in plants, potentially leading to new crop treatments and strategies for enhancing pest resistance.
The study conducted by Irene Rosa-Díaz and her colleagues highlighted the rapid response of plants to mite infestations, demonstrating how ABA plays a crucial role in reducing pest damage. Plants pre-treated with ABA to induce stomatal closure showed decreased mite damage, while ABA-deficient mutant plants with impaired stomatal function were more susceptible to mite attacks. The development of in vivo biosensors, like ABACUS2, has provided researchers with the tools to quantify cellular ABA levels and study hormone dynamics in plants with high resolution. This technology has advanced the understanding of plant defense mechanisms and the intricate signaling pathways involved in responding to environmental stresses.
As researchers further investigate the triggers of ABA accumulation in response to mite infestations, they are exploring various potential signals such as mite feeding vibrations, salivary proteins, and chemicals produced by the pests. By identifying these initial cues, researchers aim to develop new strategies for crop protection that prime plants against predicted pest infestations. Additionally, efforts to select plants with altered stomatal traits, balancing photosynthesis and water conservation, could also consider enhancing resistance to damaging pests. The findings from this research have significant implications for future crop breeding programs aimed at improving pest control on a larger scale.
