Stereochemical identification of glucans by oligothiophenes enables cellulose anatomical mapping in plant tissues

Abstract

Efficient use of plant-derived materials requires enabling technologies for non-disruptive composition analysis. The ability to identify and spatially locate polysaccharides in native plant tissues is difficult but essential. Here, we develop an optical method for cellulose identification using the structure-responsive, heptameric oligothiophene h-FTAA as molecular fluorophore. Spectrophotometric analysis of h-FTAA interacting with closely related glucans revealed an exceptional specificity for β-linked glucans. This optical, non-disruptive method for stereochemical differentiation of glycosidic linkages was next used for in situ composition analysis in plants. Multi-laser/multi-detector analysis developed herein revealed spatial localization of cellulose and structural cell wall features such as plasmodesmata and perforated sieve plates of the phloem. Simultaneous imaging of intrinsically fluorescent components revealed the spatial relationship between cell walls and other organelles, such as chloroplasts and lignified annular thickenings of the trachea, with precision at the sub-cellular scale. Our non-destructive method for cellulose identification lays the foundation for the emergence of anatomical maps of the chemical constituents in plant tissues. This rapid and versatile method will likely benefit the plant science research fields and may serve the biorefinery industry as reporter for feedstock optimization as well as in-line monitoring of cellulose reactions during standard operations.

Cellulose from the green macroalgae Ulva lactuca: isolation, characterization, optotracing, and production of cellulose nanofibrils

“…The method utilizes optotracers, a class of molecular probes called oligothiophenes, which bind selectively to glucans producing a unique spectral pattern that identifies the bound target. Applying heptameric (Choong et al 2018) and pentameric (Choong et al 2019) optotracers, cellulose can be clearly distinguished from a range of glucans and glucose-containing heteropolysaccharides based on differences in size and stereochemistry. Here, we applied optotracing as a complementary tool to overcome the limitation of HPAEC-PAD and solidstate NMR to verify the polymeric origin of the detected xylose and glucose building blocks in the extracted cellulose.…”

“…Hence, the origin of xylose in the insoluble fraction of Ulva cell walls will be very difficult to determine. A novel method for carbohydrate analysis, optotracing, opens new possibilities to determine the spatial and compositional structure of polysaccharides in plant tissues (Choong et al 2016(Choong et al , 2018(Choong et al , 2019. Oligothiophenes bind selectively to glucans and produce unique spectral patterns that are recorded by excitation and emission fluorescence spectra and allow for new insights in the polysaccharide structure of biomass samples and plant tissues.…”

Rapid diagnostic assay for detection of cellulose in urine as biomarker for biofilm-related urinary tract infections

“…A detailed analysis of the molecular interaction between h-FTAA and the cellulose polysaccharide showed an exceptional specificity to β-1,4 configured glucans. 32 This suggests a universal use of this optotracer for the detection of cellulose across biological kingdoms.…”

Stereochemical identification of glucans by a donor–acceptor–donor conjugated pentamer enables multi-carbohydrate anatomical mapping in plant tissues

“…Cellulose thus represents the only glucan identifiable by HS-84. Collectively, our experiments demonstrate that a shorter length oligomer, here shown for the pentameric Carbotrace TM 680, increases the range of detectable polysaccharides as compared to the heptameric optotracer we previously used for cellulose detection (Choong et al 2016a(Choong et al , 2018. Moreover, introducing a central BTD motif in Carbotrace TM 680 enabled a wide range of optical signatures, which is essential for the detection of multiple targets.…”

“…We applied a cationic optotracer in a novel spectrophotometric method for assessment of the purity of cellulose in fibres from pulp production and biomass extraction (Choong et al 2016b). Next, we used the anionic heptameric oligothiophene h-FTAA to produce an anatomical map of cellulose in its native location in tissues of plants (Choong et al 2018). Visualisation is based on optical detection of the cellulose specific spectral signature generated by h-FTAA aligned to b(1-4) configured glucose with DP C 8.…”