Phenolic distribution in apple epidermal and outer cortex tissue by multispectral deep-UV autofluorescence cryo-imaging

Phenolic compounds in fruit are involved in responses to biotic and abiotic stresses and are responsible for organoleptic properties. To establish the distribution of these secondary metabolites at the tissue and sub-cellular scales, mapping of fluorescence in apple epidermis and outer cortex tissue in cryogenic condition was performed after deep-UV excitation at 275 nm. Douce Moën and Guillevic cider apple varieties were sampled and frozen after harvest, after 30 days at 4 °C and after 20 days at room temperature. Image analysis of fluorescence emission images acquired between 300 and 650 nm allowed the assignment of fluorescence signals to phenolic compound families based on reference molecules. Emission attributed to monomeric and/or condensed flavanol was localized in whole tissue with major fluorescence in the cuticle region. Hydroxycinnamic acids were found predominantly in the outer cortex and appeared in the cell wall. Fluorescent pigments were mostly found in the epidermis. The distribution of flavanols in the sub-cuticle and phenolic acids in the outer cortex distinguished apple varieties. Storage conditions had no impact on phenolic distribution. The proposed fluorescent imaging and analysis approach enables studies on phenolic distribution in relation to fruit development, biotic/abiotic stress resistance and quality.

Cryo-laser scanning confocal microscopy of diffusible plant compounds

BACKGROUND

The in vivo observation of diffusible components, such as ions and small phenolic compounds, remains a challenge in turgid plant organs. The analytical techniques used to localize such components in water-rich tissue with a large field of view are lacking. It remains an issue to limit compound diffusion during sample preparation and observation processes.

RESULTS

An experimental setup involving the infusion staining of plant tissue and the cryo-fixation and cryo-sectioning of tissue samples followed by fluorescence cryo-observation by laser scanning confocal microscopy (LSCM) was developed. This setup was successfully applied to investigate the structure of the apple fruit cortex and table grape berry and was shown to be relevant for localizing calcium, potassium and flavonoid compounds.

CONCLUSION

The cryo-approach was well adapted and opens new opportunities for imaging other diffusible components in hydrated tissues.

Multi-technique characterization of poly-L-lysine dendrigrafts-Cu(II) complexes for biocatalysis

Poly-L-lysine is a biocompatible polymer used for drug or gene delivery, for transport through cellular membranes, and as nanosized magnetic resonance imaging contrast agents. Cu(II)-poly-L-lysine complexes are of particular interest for their role in biocatalysis. In this study, poly-L-lysine dendrigrafts (DGLs) at different generations (G2, G3, and G4) are synthesized and characterized in absence and presence of Cu(II) by means of electron paramagnetic resonance (EPR), UV-Vis, potentiometric titration and circular dichroism (CD). The analysis is performed as a function of the [Cu(II)]/[Lys] (=R) molar ratio, pH and generation by identifying differently flexible complexes in different dendrimer regions. The amine sites in the lateral chains become increasingly involved with the increase of pH. The good agreement and complementarity of the results from the different techniques provide an integrate view of the structural and dynamic properties of Cu(II)-DGL complexes implementing their use as biocatalysts.