Variation in sugarcane biomass composition and enzymatic saccharification of leaves, internodes and roots

Patrick J Mason,Blake Simmons,Nam V Hoang,Frederik C Botha,Gabriella Papa,Annelie Marquardt,Katrina Hodgson-Kratky,Jenny C Mortimer,Agnelo Furtado,Robert J Henry

doi:10.1186/s13068-020-01837-2

Abstract

BackgroundThe composition of biomass determines its suitability for different applications within a biorefinery system. The proportion of the major biomass fractions (sugar, cellulose, hemicellulose and lignin) may vary in different sugarcane genotypes and growth environments and different parts of the plant. This study investigated the composition of mature and immature internodes, roots and mature leaves of sugarcane.ResultsInternodes were found to have a significantly larger alcohol-soluble component than leaves and roots. The primary difference between the immature and mature internodes was the ratio of soluble sugars. In mature tissues, sucrose content was significantly higher, whereas in immature internodal tissues there was lower sucrose and heightened concentrations of reducing sugars. Carbon (C) partitioning in leaf tissues was characterised by low levels of soluble components and high “other” and cell wall fractions. Root tissue had low ratios of soluble fractions relative to their cell wall contents, indicating a lack of storage of soluble carbon. There was no significant difference in the ratio of the major cell wall fractions between the major organ types. Characterisation of individual non-cellulosic monomers indicated leaf and root tissues had significantly higher arabinose and galactose fractions. Significantly larger proportions of syringyl lignin compounds and the hydroxycinnamic compound, p-coumaric acid were observed in mature internodal tissues compared to the other tissue types. Tissue-specific differences in composition were shown to greatly affect the recalcitrance of the cell wall to enzymatic saccharification.ConclusionsOverall, this study displayed clear evidence of the differential partitioning of C throughout the sugarcane plant in specific organs. These organ-specific differences have major implications in their utility as a bioproduct feedstock. For example, the inclusion of trash (leaves) with the culms (internodes) may alter processing efficiency.

Highlights

The composition of biomass determines its suitability for different applications within a biorefinery system
Root and internodal tissue are net importers of C in the form of sucrose, i.e. sink tissues, which is cleaved into uridine diphosphate glucose (UDP-glucose) to drive cell wall expansion, hydrolysed into glucose driving respiration, or retained as sucrose for storage, [14, 15]
Cellulose has a similar correlation with lignin (R2 = 0.86, p < 0.001), as hemicellulose and lignin (R2 = 0.87, p < 0.001), whilst cellulose and hemicellulose have a higher correlation (R2 = 0.93, p < 0.001)

Summary

Introduction

The composition of biomass determines its suitability for different applications within a biorefinery system. The aforementioned factors are intrinsically linked to the way carbon (C) is partitioned within the mature sugarcane plant. Internodes, leaves, and roots utilise C in different ways throughout their life cycle, which in turn leads to distinct compositional profiles. C partitioning in sugarcane internodal tissue is unique from other organs, as C utilisation changes from one focused primarily on respiration, cell wall and protein deposition i.e. meristematic sink, to that of storage of simple sugars in the form of sucrose, i.e. a storage sink [16]. The photosynthetic nature of sugarcane leaves leads to a heightened protein profile in comparison to mature internodal tissues [17, 18]. Cell wall analysis of mature sugarcane leaves displayed significantly higher lignin and arabinose profiles in comparison to whole culm samples [19]. There is a dearth of studies in sugarcane root composition [21], no comparisons in composition or saccharification efficiency have been made

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Conclusion