Fig. 4
Colonisation of Lepidium didymum fruit valves with fungi leads to degradation of the outer pericarp layers without visible effects on the lignified endocarp. a Light microscopy (LM) of a full longitudinal fruit valve section with safranin-astrablue illustrates the distinct pericarp layers (see Fig. 6a detailing the location of the section). For the endocarp, the intense red staining indicates highly lignified thick secondary cell walls of dead cells. For the exocarp and mesocarp the blue staining of the non-lignified primary cell walls indicates living parenchymatic cells. b–d Scanning electron microscopy (SEM) of fruit valves visualising the colonisation of the outer pericarp by fungi during incubation at standard conditions. e–g LM of pericarp demonstrating the degradation of the exocarp and mesocarp layers by fungal activity after 7 days of incubation while the lignified endocarp and the seed’s testa did not show any visible degradation. The surface-sterilised control (no fungi) shows no pericarp degradation. h Effect of localised mechanical abrasion of either distal or proximal outer pericarp on the time course of pericarp rupture of surface-sterilised fruit valves (no fungi). Note that the localised mechanical abrasion was conducted in a way that the endocarp remained intact (see Supplementary Fig. 6 for details)
