Figure 3.

Spatial distribution of fluorescence lifetime in a fixed section of the rhizome of lily of the valley (C. majalis). (A) Fluorescence image of a spot-wise, 16 × 16, illuminated cell (green) overlaid on a wide-field transmission image (gray) of a region in the central parenchyma recorded using the DSLR camera. (B₁) Zoomed fluorescence image of a spot-wise illuminated cell in the central parenchyma recorded using the DSLR camera. (B₂) Fluorescence image of the same cell as in (B₁) acquired using the SPC³ SPAD camera. Fluorescence intensity is given in photon counts (PC), exposure time 46 ms. (C) Fluorescence decay curves recorded in individual SPADs at distinct intracellular locations: cell wall (black squares) and inside the cell (red circles). All fluorescence decay curves are shown in Figure S10. (D₁) A fluorescence decay curve recorded in an individual SPAD at the cell wall (black squares) fitted using a two-component exponential decay model (eq S3, red line). Inset: Corresponding residuals. (D₂) Histogram of the short fluorescence lifetime component in the plasma membrane and the best-fit Gaussian curve yield τ_f,wall1 = (0.6 ± 0.1) ns. (D₃) Histogram of the long fluorescence lifetime component in the plasma membrane and the best-fit Gaussian curve yield τ_f,wall2 = (2.9 ± 0.2) ns. (E_1–3) FLIM images of the cell in (B₂) rendered visible by mapping the: short (E₁) and long (E₂) fluorescence lifetime component and the relative contribution of the short component (E₃). In all images, the scale bar is 10 μm.