Electrochemical mapping of indole-3-acetic acid and salicylic acid in whole pea seedlings under normal conditions and salinity

Indole-3-acetic acid (IAA) and salicylic acid (SA) are two essential phytohormones for plants. Their regulating functions depend on their levels in different locations of plants. However, currently there is no satisfactory method for visual analysis of such small molecules in a whole plant. Herein the levels of IAA and SA in continuous parts of whole pea seedlings were analysed with paper-based electroanalytical devices coupled with a multichannel electrochemical station. The parts of pea seedlings were cut and put on the working electrodes for quantification. The contents of IAA and SA in continuous parts could be presented in the form of heatmaps, illustrating polar distribution of IAA levels and gradual changes of SA levels in whole pea seedlings. The contents distribution of IAA and SA further revealed variation of IAA and SA in different locations of pea seedlings. More importantly, the contents of IAA and SA in pea seedlings under normal conditions and salinity could also be differentiated with heatmaps and the contents distribution. Such results implied that our approach might be able to be extended for the study of mechanisms of plant hormones under various stresses. This study provided a possible route for visualization of small biochemical molecules in vivo with paper-based electrochemical devices.