2.5.ii. Carbohydrates and starch stains: Total carbohydrates can be stained in tissue sections using the periodic acid Schiff's or PAS technique. The classic stain for starch uses iodine in potassium iodide.

 

2.5.iii. Stains for cell viability: There are a number of fluorescent stains for assessing cell viability, however, the two fluorochromes, fluorescein diacetate (FDA) and propidium iodide are commonly used to detect living and dead cell, respectively, in tissues or cell suspensions. FDA is taken up by live cells and de-esterified to fluorescein, which fluoresces green with blue excitation. Conversely, propidium iodide is taken up by damaged or dead cells which fluoresces red with green excitation.

 

2.5.iv. Stains for microorganisms in plant tissues

Bacteria are particularly difficult to detect with the light microscope as high magnification and high resolution optics are required. Fungi are generally detected in plant tissues using the dyes methyl blue or thionin. Bacteria can be detected using Gram staining technique. The Gram stain is widely performed on dried, heat fixed smears and gives blue stain with Gram positive microorganisms and red stain with Gram negative microorganisms.

 

2.5.v. Nucleic acid stains

The earliest method to stain nucleic acid (both DNA and RNA) in section is by using acridine orange, but this requires a fluorescence microscope. For bright field optics, methyl green-pyronin method is used. However, background pyronin staining is often a problem. DNA in nuclei, mitochondria and chloroplasts can be stained using DAPI (4',6-diamidino-2-phenylindole), Hoechst 33258, Hoechst 33342 or propidium iodide.

 

2.5.vi. Lipid stains

Dyes like Sudan IV or Sudan black are generally used for staining of lipids. Nile blue is used preferentially to stain acid lipids, like phospholipids and works best on fresh tissues.