Figure 1.

Callose deposition in wheat spikes after fungal infection. A, Sections of directly inoculated wheat spikelet comprising the transition zone of rachilla and rachis including vascular bundles, as indicated in B, at 7 dpi with F. graminearum wild type (F.g. wt), lipase-deficient strain Δfgl1-2 (F.g. Δfgl1-2), and P. teres wild type (P.t. wt). Untreated spikelets served as controls. Micrographs were taken by confocal laser-scanning microscopy. Green color was assigned to fungal hyphae stained with Alexa Fluor 488-conjugated wheat germ agglutinin, and grayscale was assigned to aniline blue-stained callose. Green and grayscale channels were merged for an overview of fungal colonization of spikelet tissue, and grayscale only (aniline blue) was used to highlight callose plugs (white arrows) in the phloem of vascular bundles of the transition zone. Micrographs are representative for infection at 7 dpi. Bars = 200 µm (left column) and 100 µm (middle column). The right column provides a macroscopic overview of the disease severity of directly inoculated spikelets at 14 dpi. B, Longitudinal section of wheat spikelets and rachis to highlight the transition zone of rachilla and rachis including vascular bundles (white arrows). The orange frame indicates the area of microscopic analysis in A. Bars = 1 mm. C, Number of callose plugs located in the phloem of vascular bundles of the transition zone of rachilla and rachis tissue from directly inoculated spikelets as analyzed in A at 1, 3, 7, and 14 dpi with F. graminearum wild type, lipase-deficient strain Δfgl1-2, and P. teres wild type. Untreated spikelets served as controls. Values represent means of eight biologically independent inoculation experiments for each fungal strain. The letters a, b, and c indicate P < 0.05 by Tukey’s test. Error bars represent se, and n = 8. D, High-resolution microscopy of callose deposition (fluorescence by aniline blue staining) in sieve elements (indicated by dotted lines) of the phloem in the transition zone of rachilla and rachis of control and infected wheat spikelets. Callose plugs in sieve elements of Δfgl1-2-infected spikelets are representative for P. teres-induced callose plugs. cd, Callose deposit; se, sieve element; sp, sieve plate. Bars = 20 µm.