Resolving diurnal dynamics of the chloroplastic glutathione redox state in Arabidopsis reveals its photosynthetically derived oxidation

Plants are subjected to fluctuations in light intensity, and this might cause unbalanced photosynthetic electron fluxes and overproduction of reactive oxygen species (ROS). Electrons needed for ROS detoxification are drawn, at least partially, from the cellular glutathione (GSH) pool via the ascorbate–glutathione cycle. Here, we explore the dynamics of the chloroplastic glutathione redox potential (chl-E_GSH) using high-temporal-resolution monitoring of Arabidopsis (Arabidopsis thaliana) lines expressing the reduction–oxidation sensitive green fluorescent protein 2 (roGFP2) in chloroplasts. This was carried out over several days under dynamic environmental conditions and in correlation with PSII operating efficiency. Peaks in chl-E_GSH oxidation during dark-to-light and light-to-dark transitions were observed. Increasing light intensities triggered a binary oxidation response, with a threshold around the light saturating point, suggesting two regulated oxidative states of the chl-E_GSH. These patterns were not affected in npq1 plants, which are impaired in non-photochemical quenching. Oscillations between the two oxidation states were observed under fluctuating light in WT and npq1 plants, but not in pgr5 plants, suggesting a role for PSI photoinhibition in regulating the chl-E_GSH dynamics. Remarkably, pgr5 plants showed an increase in chl-E_GSH oxidation during the nights following light stresses, linking daytime photoinhibition and nighttime GSH metabolism. This work provides a systematic view of the dynamics of the in vivo chloroplastic glutathione redox state during varying light conditions.

Monitoring the daily in vivo dynamics of the chloroplastic GSH redox state in light-stressed wild-type plants versus photoprotective mutants provides insight into the photosynthesis-dependent production of oxidants.     

Optically derived metabolic and hemodynamic parameters predict hippocampal neurogenesis in the BTBR mouse model of autism

In this study, we made use of dual‐wavelength laser speckle imaging (DW‐LSI) to assess cerebral blood flow (CBF) in the BTBR‐genetic mouse model of autism spectrum disorder, as well as control (C57Bl/6J) mice. Since the deficits in social behavior demonstrated by BTBR mice are attributed to changes in neural tissue structure and function, we postulated that these changes can be detected optically using DW‐LSI. BTBR mice demonstrated reductions in both CBF and cerebral oxygen metabolism (CMRO₂), as suggested by studies using conventional neuroimaging technologies to reflect impaired neuronal activation and cognitive function. To validate the monitoring of CBF by DW‐LSI, measurements with laser Doppler flowmetry (LDF) were also performed which confirmed the lowered CBF in the autistic‐like group. Furthermore, we found in vivo cortical CBF measurements to predict the rate of hippocampal neurogenesis, measured ex vivo by the number of neurons expressing doublecortin or the cellular proliferation marker Ki‐67 in the dentate gyrus, with a strong positive correlation between CBF and neurogenesis markers (Pearson, r = 0.78; 0.9, respectively). These novel findings identifying cortical CBF as a predictive parameter of hippocampal neurogenesis highlight the power and flexibility of the DW‐LSI and LDF setups for studying neurogenesis trends under normal and pathological conditions.      

Sensing stress responses in potato with whole-plant redox imaging

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 (E_GSH). 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 E_GSH under several stress conditions including, high-light (HL), cold, and drought. An extremely high increase in chloroplast E_GSH 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.

Whole-plant imaging of potato plants expressing a genetically encoded biosensor allows for spatially resolved and nondestructive mapping of stress-induced redox perturbations.