X-ray micro-computed tomography in willow reveals tissue patterning of reaction wood and delay in programmed cell death.

Nicholas Brereton,Daniel Sykes,Richard Murphy,Ian Shield,Angela Karp,Farah Ahmed,Michael Ray

doi:10.1186/s12870-015-0438-0

Abstract

BackgroundVariation in the reaction wood (RW) response has been shown to be a principle component driving differences in lignocellulosic sugar yield from the bioenergy crop willow. The phenotypic cause(s) behind these differences in sugar yield, beyond their common elicitor, however, remain unclear. Here we use X-ray micro-computed tomography (μCT) to investigate RW-associated alterations in secondary xylem tissue patterning in three dimensions (3D).ResultsMajor architectural alterations were successfully quantified in 3D and attributed to RW induction. Whilst the frequency of vessels was reduced in tension wood tissue (TW), the total vessel volume was significantly increased. Interestingly, a delay in programmed-cell-death (PCD) associated with TW was also clearly observed and readily quantified by μCT.ConclusionsThe surprising degree to which the volume of vessels was increased illustrates the substantial xylem tissue remodelling involved in reaction wood formation. The remodelling suggests an important physiological compromise between structural and hydraulic architecture necessary for extensive alteration of biomass and helps to demonstrate the power of improving our perspective of cell and tissue architecture. The precise observation of xylem tissue development and quantification of the extent of delay in PCD provides a valuable and exciting insight into this bioenergy crop trait.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0438-0) contains supplementary material, which is available to authorized users.

Highlights

Variation in the reaction wood (RW) response has been shown to be a principle component driving differences in lignocellulosic sugar yield from the bioenergy crop willow
Density and G-layer verification The basic density of 2–4 cm long stem middle segments from 3 month old willow was assessed after trees had been tipped for 6 weeks of their growth or grown vertically as controls
RW response has been identified as a principle cause of variation in enzymatic saccharification yields in willow, yet understanding of the tissue architectural and cellular remodelling associated with RW has typically been limited to classical sectioning and microscopy

Summary

Introduction

Variation in the reaction wood (RW) response has been shown to be a principle component driving differences in lignocellulosic sugar yield from the bioenergy crop willow. The glucose rich cell walls of dedicated bioenergy crops (such as willow or Miscanthus in the UK) are generally recalcitrant to deconstruction, requiring high amounts of energy and severe chemical pretreatment before the glucose can be released in a form suitable for fermentation. To overcome this barrier, research efforts worldwide have been. RW formation in trees is characterised by major alterations in xylem cell development and tissue patterning in the stem in response to displacement from vertical, either through the perception of gravity or mechanical load. Despite being recognised as a key determinant of glucose yield, many aspects of this trait, and how the trait

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