Tetrazoliumtests

Tetrazolium tests are a family of colorimetric assays used to estimate cell viability and metabolic activity by exploiting the ability of living cells to reduce tetrazolium salts to colored formazan compounds. In cell-based assays, commonly used reagents include MTT, MTS, XTT, and the water-soluble salts WST-1 and WST-8; a related application in plant biology uses the tetrazolium salt TTC (2,3,5-triphenyltetrazolium chloride) for seed viability testing.

The underlying principle is that active cellular dehydrogenases, principally in mitochondria, reduce the tetrazolium salt to a colored formazan. The amount of formazan produced correlates with the number of viable, metabolically active cells. Some reagents yield insoluble formazan (e.g., MTT), requiring a solubilization step before spectrophotometric measurement, while others generate soluble formazan directly (e.g., MTS, WST-1, WST-8), allowing straightforward readouts.

Protocols typically involve exposing cells or tissues to the reagent, incubating for a defined period, and measuring absorbance with a spectrophotometer. Absorbance is usually read in the 490–570 nm range, depending on the specific reagent. In seed testing, TTC is reduced to a red formazan in viable tissues, enabling estimation of viability percentages.

Applications include cytotoxicity testing, cell proliferation assays, and high-throughput screening, as well as seed and tissue viability assessments in plants. Limitations include interference from media components and reducing agents, dependence on metabolic activity rather than direct cell count, and, for insoluble formulations, the need for solubilization steps.