Résumé
The differences in digestibility or degradability of lignocellulosic biomass could be explained by the relative proportions and compositions of plant tissues, in particular the lignin distribution [1]. We apply quantitative histology approaches to obtain objective features with the aim of comparing several genotypes. Macroscopic imaging is required to study large samples such as whole stem sections of about 1 cm². At this scale, morphological features such as stem area, rind thickness, vascular bundle density can be obtained. Fluorescence macrovision allows the detection of lignin and phenolic acids thanks to their autofluorescence properties. We propose to use both types of imaging with the goal of highlighting variability in maize stem tissues for a series of 14 maize genotypes.Two types of images were acquired. Visible images were obtained using a dedicated device equipped with darkfield illumination. UV and visible fluorescence multispectral images were acquired using a fluorescence macroscope. Rind, vascular bundles and parenchyma were segmented in both images. About twenty morphological features including the proportion of tissues were measured from darkfield images. Autofluorescence pseudo-spectra were extracted from the multispectral images for each tissue [2]. Principal component analysis was applied to reveal the variability of the 14 genotypes.Using the morphological features, we were able to observe a huge variability between the 14 genotypes based on tissue proportion, opposing them on vascular bundle individual area, rind area and vascular bundle density. Stem area and cells diameter were also contrasted between genotypes. Using the pseudo-spectra measured for each tissue of each genotype, the fluorescence properties were mainly found to be tissue-specific and to a lesser extent genotype-specific. As expected, parenchyma tissues were less fluorescent after visible excitation compared to the rind and vascular bundles, this fluorescence being assigned to lignin. Depending on the genotype, the parenchyma near the rind was more or less differentiated from the middle parenchyma. The autofluorescence pseudo-spectra of the lignified tissues could be associated with colocalization of hydrodynamic acids and lignin.The proposed method using two macrovision devices allows us to observe variability in our selected genotypes. This variability is related to the proportion and the composition of observed tissues in the maize stem. The method is quite simple and can be adapted to many purposes and materials.