Fig. 4

a Merged optical and ~ 1520 cm⁻¹ Raman images (outlined in red) of maize leaf transverse cross sections. From left to right the images correspond to FoMV-pds silenced, FoMV, and non-inoculated leaves. The color scale represents the Raman scattering intensity as shown in the scale at right. The scale bar is 25 µm. Additional transverse cross section Raman images are shown in Additional file 1: Fig. S6. b Histograms of the ~ 1520 cm⁻¹ peak maximum were generated from each pixel in the Raman images shown in a and Additional file 1: Fig. S6. The histograms were fit to a Gaussian function (red solid line). N is the number of pixels that were positive for carotenoids and N′ is the number of pixels that were null (not included in the histogram)