Unraveling Phytosulfokine Trafficking in Arabidopsis thaliana Using Fiber-Optic Fluorescence Microscopy

As sessile organisms, plants manage stress through complex signaling networks involving phytohormones such as phytosulfokine (PSK). PSK, a disulfated pentapeptide, regulates plant growth, development, and stress responses by interacting with specific PSK receptors (PSKRs). In this study, we explored the trafficking dynamics of PSK, its post-application fate, and the synthesis of an analog. We administered both native PSK and a fluorescent version tagged with TAMRA (5(6)-carboxytetramethylrhodamine) to various Arabidopsis thaliana genotypes, including wild type, a PSKR-deficient mutant, and a strain overexpressing PSKR1 tagged with green fluorescent protein (GFP) over the wild-type background. Fiber-optic fluorescence microscopy revealed that receptor presence influences PSK’s internal movement. Additionally, we extracted TAMRA–PSK from treated plants and recovered it using solid-phase extraction to assess its stability post-application. HPLC analysis suggested that TAMRA–PSK is substantially unchanged in the plant matrix. Furthermore, a PSK analog was partially synthesized via solid-phase peptide synthesis for future studies.