Paper-based electroanalytical devices for in situ determination of free 3-indoleacetic acid and salicylic acid in living Pyropia haitanensis thallus under various environmental stresses

Phytohormones play a vital role in regulating plant developmental processes and signaling for defense, but little is known of the specific functions of phytohormones in Pyropia haitanensis. In this study, paper-based electroanalytical devices for sensitive, in situ detection of free 3-indoleacetic acid (IAA) and salicylic acid (SA) based on their electrocatalytic oxidation under differential pulse voltammetry in P. haitanensis thallus were built. Then, this method was used to detect free IAA and SA in P. haitanensis thallus under different environmental stresses, including high temperature, high irradiance, desiccation, and exposure to ultraviolet radiation. The concentrations of SA increased after the different environmental stresses were imposed, while the concentrations of IAA significantly decreased after desiccation, exposure to ultraviolet radiation and high light. During exposure to high temperature, the concentrations of IAA increased in the first hour after treatment, and then returned to the normal level for the following 5 h. All of the electrocatalytic measurements were supported by measuring expression levels of IAA and SA synthesis-related genes in P. haitanensis. These results help to systematically clarify that IAA acts as a negative regulatory factor in regulating plant resistance to environmental stresses except for high temperature, while SA plays the opposite role.