Functional plant cell wall design revealed by the Raman imaging approach

Abstract

Using the Raman imaging approach, the optimization of the plant cell wall design was investigated on the micron level within different tissue types at different positions of a Phormium tenax leaf. Pectin and lignin distribution were visualized and the cellulose microfibril angle (MFA) of the cell walls was determined. A detailed analysis of the Raman spectra extracted from the selected regions, allowed a semi-quantitative comparison of the chemical composition of the investigated tissue types on the micron level. The cell corners of the parenchyma revealed almost pure pectin and the cell wall an amount of 38-49% thereof. Slight lignification was observed in the parenchyma and collenchyma in the top of the leaf and a high variability (7-44%) in the sclerenchyma. In the cell corners and in the cell wall of the sclerenchymatic fibres surrounding the vascular tissue, the highest lignification was observed, which can act as a barrier and protection of the vascular tissue. In the sclerenchyma high variable MFA (4°-40°) was detected, which was related with lignin variability. In the primary cell walls a constant high MFA (57°-58°) was found together with pectin. The different plant cell wall designs on the tissue and microlevel involve changes in chemical composition as well as cellulose microfibril alignment and are discussed and related according to the development and function.

Raman Imaging of Lignocellulosic Feedstock

“…In the Raman spectrum the region between 860-825 cm -1 corresponds to equatorial anomeric H (α-anomers and α-glycosides), whereas the band at about 900-880 cm -1 corresponds to axial anomeric H (β-anomers and β-glycosides) [147]. The sharp Raman band between 860 and 854 cm -1 is characteristic for pectin and shows no overlap with the other plant cell wall polymers and can therefore be used as a marker band in the imaging approach [148,149]. Furthermore the exact position of this band is sensitive to the state of uronic carboxyls and to O-acetylation thus providing insight into pectin structure; decreasing with methylation (min.…”

“…By calculating the integral of the bands in the Raman spectra of plant cell walls the distribution of different molecular structures can be imaged on the micron-level [148,149,167,183]. Figure 5A shows an example of imaging water uptake of cell walls in young poplar wood (Populus nigra x Populus deltoids) by plotting the integral of the OH stretching vibration.…”

Topochemical Correlation between Carbohydrates and Lignin in Eucommia ulmoides Cell Wall from Tissue to Cell Level

“…In addition, sample isolation difficulties arise when small cell wall areas or single layers are of interest because they have to be carefully excised. Advances in confocal Raman microscopy and imaging have tackled this problem in a noninvasive way to provide chemical and structural information in situ with a high spatial resolution (< 0.5 μm) (Agarwal et al 2011;Richter et al 2011;Prats et al 2016). Both lignin and carbohydrates can be mapped simultaneously by selecting the Raman bands that are specific to these cell wall components.…”

Espectroscopía Ultrasónica Resonante Sin Contacto y su Aplicación al Estudio de Tejidos Vegetales en Estructura Multicapa = Non-Contact Resonant Ultrasound Spectroscopy and its Application to Study Multilayered Vegetal Tissues

“…The structure of the P. tenax leaf has been the object of previous studies, further details can be seen in Richter et al, 2011;and Arévalo et al (2013). Measurements were taken at the central part of the leaf (unfolded distal part) over a total distance of about 500 mm.…”

“…Mechanical measurements in different directions in the whole leaf by have shown a longitudinal and transverse stiffness of 3.9870.99 GPa and 0.02270.002 GPa, respectively. Functional design of the cell wall has been studied by a Raman imaging approach by Richter et al (2011).…”