Immunohistochemical analyses on two distinct internodes of stinging nettle show different distribution of polysaccharides and proteins in the cell walls of bast fibers

Claudia Faleri,Xuan Xu,Lavinia Mareri,Jean-Francois Hausman,Giampiero Cai,Gea Guerriero

doi:10.1007/s00709-021-01641-1

Claudia Faleri, Xuan Xu + Show 4 more

Open Access

https://doi.org/10.1007/s00709-021-01641-1

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Abstract

Stinging nettle is a perennial herbaceous species holding value as a multi-purpose plant. Indeed, its leaves and roots are phytofactories providing functional ingredients of medicinal interest and its stems produce silky and resistant extraxylary fibers (a.k.a. bast fibers) valued in the biocomposite sector. Similarly to what is reported in other fiber crops, the stem of nettle contains both lignified and hypolignified fibers in the core and cortex, respectively, and it is therefore a useful model for cell wall research. Indeed, data on nettle stem tissues can be compared to those obtained in other models, such as hemp and flax, to support hypotheses on the differentiation and development of bast fibers. The suitability of the nettle stem as model for cell wall-related research was already validated using a transcriptomics and biochemical approach focused on internodes at different developmental stages sampled at the top, middle, and bottom of the stem. We here sought to complement and enrich these data by providing immunohistochemical and ultrastructural details on young and older stem internodes. Antibodies recognizing non-cellulosic polysaccharides (galactans, arabinans, rhamnogalacturonans) and arabinogalactan proteins were here investigated with the goal of understanding whether their distribution changes in the stem tissues in relation to the bast fiber and vascular tissue development. The results obtained indicate that the occurrence and distribution of cell wall polysaccharides and proteins differ between young and older internodes and that these changes are particularly evident in the bast fibers.

Highlights

The exploitation of plant biomass as a source of energy and of added-value molecules for industrial applications is a pressing demand to promote a bioeconomy that is both sustainable and environmentally friendly
At the level of top internode, bast fibers have been identified following a positionalbased approach; essentially, we first focused on vascular bundles, we moved on the region immediately outside the phloem where two cell types could be essentially found, one of parenchymatous type with only primary cell wall (PCW) and a cell type showing onset of secondary cell wall (SCW) formation
The nettle stem sections were collected on gold grids and blocked for 20 min with normal goat serum (NGS) diluted 1:30 in dilution buffer (0.05 M Tris-HCl pH 7.6, 0.9% w/v NaCl, and 0. 2% w/v BSA)

Summary

Introduction

The exploitation of plant biomass as a source of energy and of added-value molecules for industrial applications is a pressing demand to promote a bioeconomy that is both sustainable and environmentally friendly. Plants that produce bast fibers are interesting because they supply both long and strong fibers containing considerable amounts of crystalline cellulose. Examples of such plants are flax and hemp. Bast fibers are used in the textile industry and by the biocomposite sector as eco-friendly alternatives to artificial fibers While species such as flax and hemp have gained remarkable interest from the scientific community, nettle (Urtica dioica L.) has not been studied as much, it is considered one of the most underrated plants among those of potential economic interest (Di Virgilio et al 2015). The availability of its transcriptome and of high-throughput RNA-Seq datasets (Xu et al 2019; Carpenter et al 2019) favors molecular comparisons with other fiber crop models

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