Abstract
The proportion and composition of plant tissues in maize stems vary with genotype and agroclimatic factors and may impact the final biomass use. In this manuscript, we propose a quantitative histology approach without any section labelling to estimate the proportion of different tissues in maize stem sections as well as their chemical characteristics. Macroscopic imaging was chosen to observe the entire section of a stem. Darkfield illumination was retained to visualise the whole stem cellular structure. Multispectral autofluorescence images were acquired to detect cell wall phenolic compounds after UV and visible excitations. Image analysis was implemented to extract morphological features and autofluorescence pseudospectra. By assimilating the internode to a cylinder, the relative proportions of tissues in the internode were estimated from their relative areas in the sections. The approach was applied to study a series of 14 maize inbred lines. Considerable variability was revealed among the 14 inbred lines for both anatomical and chemical traits. The most discriminant morphological descriptors were the relative amount of rind and parenchyma tissues together with the density and size of the individual bundles, the area of stem and the parenchyma cell diameter. The rind, as the most lignified tissue, showed strong visible-induced fluorescence which was line-dependant. The relative amount of para-coumaric acid was associated with the UV-induced fluorescence intensity in the rind and in the parenchyma near the rind, while ferulic acid amount was significantly correlated mainly with the parenchyma near the rind. The correlation between lignin and the tissue pseudospectra showed that a global higher amount of lignin resulted in a higher level of lignin fluorescence whatever the tissues. We demonstrated here the potential of darkfield and autofluorescence imaging coupled with image analysis to quantify histology of maize stem and highlight variability between different lines.
Highlights
Maize is a major productive crop worldwide and the most widely used forage crop in dairy cow feeding (Boon et al, 2008; BarrosRios et al, 2012; Barriere, 2017)
Para-coumaric acid, which accounts for approximately 1.5–2.5% of the cell wall, is mainly associated with lignin, while ferulic acid, which accounts for approximately 0.7% of the cell wall, is ether linked to lignin or ester linked to hemicelluloses (Ralph et al, 1998; Méchin et al, 2000; Jung and Casler, 2006a; Barrière et al, 2009a; Hatfield et al, 2017)
We developed a quantitative histology approach to estimate the proportion of different tissues in maize stem sections and associated a chemical profile with each of these tissues
Summary
Maize is a major productive crop worldwide and the most widely used forage crop in dairy cow feeding (Boon et al, 2008; BarrosRios et al, 2012; Barriere, 2017). The amount of lignins in the cell wall, their variable structure, and the cross-linkages between cell wall components have been suggested to have a variable depressive effect on cell wall polysaccharide degradation by enzymes or microorganisms (Méchin et al, 2000; Fontaine et al, 2003; Jung and Phillips, 2010; Barriere, 2017; Casler and Jung, 2017; Hatfield et al, 2017; Terrett and Dupree, 2019). The main determinant among these factors for recalcitrance is still not clear (McCann and Carpita, 2015; Melati et al, 2019; Zoghlami and Paës, 2019), which is partly due to the large variability of biomass and assignment of biomass as a bulk material without considering the heterogeneity of plant cell walls according to organs and tissues
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