Calcium Based Systemic Activation of Plant Defense by Exposure to Plasma-generated N₂O₅

Recently, we have developed a new air atmospheric pressure plasma (APP) system that allows selective production of dinitrogen pentoxide (N₂O₅). N₂O₅ is a promising chemical for a variety of applications, but it has not been used widely due to the difficulties of its production and storage. Our APP device/method enables in-situ production and supply of N₂O₅ with easy handling. Here, we explored the applicability of the APP-generated N₂O₅ in agriculture. O₃ exposure has been reported to induce systemic acquired resistance in the phytohormone salicylic acid pathway, which generally causes growth retardation. On the other hand, we found that N₂O₅ exposure can induce plant defensin genes such as PDF1.2 that follow a jasmonic acid (JA) pathway without growth retardation in Arabidopsis thaliana. Cytosolic Ca²⁺ concentration was increased in a single leaf directly exposed to N₂O₅ and the Ca²⁺ signal propagated to non-exposed leaves within 1 min. The Ca²⁺ response is similar to a wound-induced response, which elicits a systemic defense response by JA. We also found that expression of JA-related genes was significantly induced in both exposed and non-exposed leaves. These results indicate that the APP-generated N₂O₅ exposure provokes a systemic defense response without growth retardation.