The root tissue is already incubated in the DAF-FM DA and washed with HEPES-KOH buffer. But due to non-availability of confocal microscope on the same day, is it possible to store the tissue in HEPES-KOH buffer at room temperature?
DAF-FM Diacetate reacts with NO and forms benzotriazole (which fluoresce) and can be detected. I don't know for how much time you incubated the root tissues with DAF because it reacts and forms benzotriazole. Then it will be difficult to to save the NO in the root tissues and you might not get the right results. I think avoid and prepare the samples freshly when instrument is ready.