Fig. 3

Laser confocal microscopic images of F. graminearum infection of wheat coleoptiles at 16 hpi. Tissue cells of wheat coleoptiles were stained with PI (Propidium iodide) (red). a A 3D image showing extracellular hyphae traversing the cell wall of wheat coleoptiles through pits. Asterisks indicate penetration sites. This image is a 3D reconstruction of 31 optical sections acquired with a z-interval of 0.35 μm. b Extracellular hyphae began to penetrate the cell wall of wheat coleoptiles at 16 hpi. Detailed views of each boxed region are shown. It could be seen that penetration pegs experience extreme constriction (about 1 μm) as they penetrate the wheat coleoptiles cell walls. c, d Bulbous and vacuolar hyphae are formed in the intercellular space of wheat coleoptiles at 16 hpi. Potential and existing penetration sites are indicated with asterisks. e A proposed model depicting the early stages (8–16 hpi) of F. graminearum proliferation inside wheat coleoptiles