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. 2018 Feb 19;9:199. doi: 10.3389/fpls.2018.00199

FIGURE 3.

FIGURE 3

Defense responses and pathogen infection observed in root epidermis and cortical tissues of resistant pea accessions after inoculation with Fop race 2. Arrows indicate fungus. (A) Longitudinal section of the partially resistant Messire stained with TBO at 4 days post-inoculation (dpi) showing cell wall lignification (Green arrows) at epidermis (Ep) and the formation of a papilla at the exodermis (Ex) to prevent Fop hypha penetration. (B) TBO-stained cross-section of the resistant accession P42 at 4 dpi showing formation of papillae (P) in the epidermis at site of attempted fungal penetration. (C) Cross-section of the partially resistant accession Messire at 4 dpi, stained with TBO, showing the lignification of cortical cell walls (Green arrows) to prevent hypha penetration into cortical cells (Co). (D) TBO-stained cross-section of resistant accession JI1412 roots at 4 dpi showing the lignification of cortical cell wall (Green arrows) and formation of papillae (P) impeding fungal entry into cortical cells, although the fungi can progress through the cortex intercellularly (Black arrows). (E) Cross-section of the resistant accession JI1760 roots at 7 dpi, stained with alcian green:safranin mixture (AGS), showing papillae and the accumulation of undetermined substances (red staining indicated by Blue arrows) in the intercellular space of cortical cells. (F) The same cross-section as (E) observed by epi-fluorescence showing the blue-violet fluorescence of papillae and two types of fluorescent emission corresponding to the substances accumulated between cortical cells, blue (Blue arrowheads corresponding to lignin) and orange (Red arrowheads). (G) TBO-stained longitudinal section of the resistant accession P633 at 4 dpi showing accumulation of phenolic substances (turquoise green staining indicated by arrowheads) at epidermis in presence of fungi. (H) TBO-stained cross-section of the resistant accession P633 roots at 4 dpi showing the accumulation of phenolic substances (Blue arrows) between cortical cells. Bar = 25 μm.