I have harvested pollen grains from Periwinkle using needle and forceps an resuspended them in PBS/normal saline. Then I assessed their viability using the Sysmex Pollen Viability Kit (Fluorescein diacetate and Propidium iodide) using a flow cytometer. I have found that majority of the pollen grains are dead (negative for green fluorescence). Do you think the pollen grains are damaged during harvesting? If yes, what is the solution? Is the lifespan of Periwinkle pollen grains too little? In one of my experiments I used PBS with Na.azide by mistake. Is Na.azide toxic to pollen grains?