4.2. Safranin O Staining

Safranin O (Sigma, S8884,Munich, Germany) was dissolved in water (5 mg/mL), as previously reported [24]; the whole plants or excised leaves were harvested at the indicated time points and submerged into a safranin O solution for 0.5–1 h, allowing the dye to enter the tissue from the stomata and incision. Next, the material was washed with water to remove the surplus dye. The stained starch granules were visualized in the background of chloroplast auto-fluorescence with a strong contrast by selecting the proper pseudo-color.