Abstract
The properties of the secondary cell wall (SCW) in willow largely determine the suitability of willow biomass feedstock for potential bioenergy and biofuel applications. SCW development has been little studied in willow and it is not known how willow compares with model species, particularly the closely related genus Populus. To address this and relate SCW synthesis to candidate genes in willow, a tractable bud culture-derived system was developed in Salix purpurea, and cell wall composition and RNA-Seq transcriptome were followed in stems during early development. A large increase in SCW deposition in the period 0–2 weeks after transfer to soil was characterised by a big increase in xylan content, but no change in the frequency of substitution of xylan with glucuronic acid, and increased abundance of putative transcripts for synthesis of SCW cellulose, xylan and lignin. Histochemical staining and immunolabeling revealed that increased deposition of lignin and xylan was associated with xylem, xylem fibre cells and phloem fibre cells. Transcripts orthologous to those encoding xylan synthase components IRX9 and IRX10 and xylan glucuronyl transferase GUX1 in Arabidopsis were co-expressed, and showed the same spatial pattern of expression revealed by in situ hybridisation at four developmental stages, with abundant expression in proto-xylem, xylem fibre and ray parenchyma cells and some expression in phloem fibre cells. The results show a close similarity with SCW development in Populus species, but also give novel information on the relationship between spatial and temporal variation in xylan-related transcripts and xylan composition.Electronic supplementary materialThe online version of this article (doi:10.1007/s00425-014-2034-1) contains supplementary material, which is available to authorized users.
Highlights
Plant biomass has potential as a major renewable source of energy and transport fuels
Improvement of willow as a biofuel crop requires an improved understanding of the composition of willow wood and secondary cell walls (SCW), since the sugars needed for conversion for biofuels are derived from lignocellulose
To relate SCW synthesis to candidate genes in willow, we developed a tractable system, based on re-growth from axillary buds, to study composition and gene expression of developing willow stems in a standardised, controlled way
Summary
Plant biomass has potential as a major renewable source of energy (bioenergy) and transport fuels (biofuels). Planta (2014) 239:1041–1053 as short rotation coppice, are among the leading commercially grown biomass trees in temperate regions (Karp et al 2011). They are highly diverse and the circa 400 species are broadly grouped into three main subgenera: the tree willows (sub-genus Salix), the dwarf and alpine willows (sub-genus Chamaetia) and the shrubby willows (sub-genus Vetrix). The shrubby willows are the most suited for biomass due to their propensity for fast, vigorous growth in coppicing cycles, low fertilisation requirements (an average of 20–30 kg N ha−1 year−1) and ease of vegetative propagation. Willows have been considered as a potential feedstock source for biofuels. Improvement of willow as a biofuel crop requires an improved understanding of the composition of willow wood and secondary cell walls (SCW), since the sugars needed for conversion for biofuels are derived from lignocellulose
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