(a) Confocal images of VF36 and flavonol-deficient are mutant pollen grains stained with fluorescein diacetate (FDA, green; live grains) and propidium iodide (PI, magenta; dead grains) and scanning electron micrographs show that the are mutant produces less viable pollen. Scale bars = 200 μm for confocal images and 20 μm for electron micrographs, (b) The general ROS sensor, DCF, and the H2O2-selective chemical probe, Peroxy orange 1 (PO1) reveal increased ROS accumulation in pollen grains of the are mutant. Scale bar = 50 μm (c) Confocal micrographs display significantly impaired pollen tube growth as well as increased levels of ROS in the are mutant. Scale bar = 50 μm (top) and 100 μm (bottom). Adapted from Ref. [18]. Copyright 2018 Proceedings of the National Academy of Sciences.