Environmental stresses are among the major factors that limit crop productivity and plant growth. Various nondestructive approaches for monitoring plant stress states have been developed. However, early sensing of the initial biochemical events during stress responses remains a significant challenge. In this work, we established whole-plant redox imaging using potato (Solanum tuberosum) plants expressing a chloroplast-targeted redox-sensitive green fluorescence protein 2 (roGFP2), which reports the glutathione redox potential (EGSH). Ratiometric imaging analysis demonstrated the probe response to redox perturbations induced by H2O2, DTT, or a GSH biosynthesis inhibitor. We mapped alterations in the chloroplast EGSH under several stress conditions including, high-light (HL), cold, and drought. An extremely high increase in chloroplast EGSH was observed under the combination of HL and low temperatures, conditions that specifically induce PSI photoinhibition. Intriguingly, we noted a higher reduced state in newly developed compared with mature leaves under steady-state and stress conditions, suggesting a graded stress sensitivity as part of the plant strategies for coping with stress. The presented observations suggest that whole-plant redox imaging can serve as a powerful tool for the basic understanding of plant stress responses and applied agricultural research, such as toward improving phenotyping capabilities in breeding programs and early detection of stress responses in the field.
