Photobleaching analysis. Romaine lettuce samples with a thickness of 10 mm were imaged using a Nikon Ti-2 inverted microscope under the Cy5 fluorescence channel (649 nm/666 nm) for over four minutes. Images were automatically taken every 300 ms at an exposure time of 1s and the mean fluorescence intensity of the collected images were quantified. This procedure was repeated three times to ensure reproducibility of the observed trend.