Neutral Red

This dye has been widely used in many staining methods, but its commonest use is probably as a simple red nuclear counterstain. It is an indicator as well as a dye. It changes from red to yellow over the pH range 6.8–8.0. It has also been incorporated into bacteriological growth media.

Neutral red dye is a dark brown to dark green power used to stain nuclei red, in cell viability tests, and as a pH indicator (transition of pH indicator: pH 6.8–8.0, red to yellow). Additionally, it is used to prepare neutral red paper and as a histological stain for lysozymes. It is available in three qualities commercially each differing in the dye content as 60%, 90% and 95% as mentioned in the specs by producer GSPChem.

Methods NR was used as a fluorochrome for living roots of Phaseolus vulgaris, Allium cepa, A. porrum and Arabidopsis thaliana (wild-type and transgenic GFP-carrying lines). The tissues were visualized using CLSM. The effect of NR on the integrity of the cytoskeleton and the growth rate of arabidopsis primary roots was analysed to judge potential toxic effects of the dye.

The main advantages of the use of NR are related to the fact that NR rapidly penetrates root tissues, has affinity to suberin and lignin, and accumulates in the vacuoles. It is shown that NR is a suitable probe for visualization of proto- and metaxylem elements, Casparian bands in the endodermis, and vacuoles in cells of living roots. The actin cytoskeleton and the microtubule system of the cells, as well as the dynamics of root growth, remain unchanged after short-term application of NR, indicating a relatively low toxicity of this chemical. It was also found that NR is a useful probe for the observation of the internal structures of root nodules and of fungal hyphae in vesicular–arbuscular mycorrhizas.