#cell viability

Plant tissue culture 2

Dead protoplasts are stained red by:

Dead protoplasts are stained red by propidium iodide PI nucleic acid intercalating fluorescent dye that distinguishes membrane compromised cells. PI is cationic molecule unable to cross intact lipid bilayer of viable protoplasts due to charge and size exclusion, so viable population excludes dye remaining unstained. In dead cells membrane integrity lost through enzymatic damage or physical stress, PI diffuses entering cytoplasm nucleus where it intercalates between double stranded DNA and RNA base pairs with strong affinity, enhancing red fluorescence emission at 617 nm when excited green light 535 nm. Under fluorescence microscope dead protoplasts show bright red nucleus clearly differentiated from viable green FDA positive cells in dual viability test. This assay allows rapid quantitative assessment of protoplast isolation success and cytotoxicity of fusogen treatments. Compared to colorimetric dyes like Evans blue which stains dead cells blue but requires bright field observation, PI provides fluorescent contrast compatible with flow cytometric analysis sorting live cells for downstream culture fusion transformation. Maintaining membrane integrity crucial because only viable protoplasts can regenerate wall divide form microcallus and participate in heterokaryon formation during somatic hybridization procedures.

Ref: Jones 1987 PI dead staining; Molecular Probes Handbook viability dyes.

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Plant tissue culture 2

Viable protoplasts fluoresce green when stained with:

Viable protoplasts fluoresce bright green when stained with fluorescein diacetate FDA, vital fluorescent dye used routinely for viability assessment before fusion or transformation to ensure batch quality above 80 percent. FDA itself is non fluorescent lipophilic molecule that diffuses across intact plasma membrane permeable only to living cells with intact barrier. Inside cytoplasm active non specific esterases present exclusively in living cells hydrolyze ester bonds releasing fluorescein highly fluorescent polar molecule that accumulates inside membrane intact vesicle because its negative charge prevents efflux, emitting green fluorescence 520 nm upon excitation blue light 490 nm under fluorescence microscope. Dead protoplasts with compromised membranes lack esterase activity and cannot retain fluorescein thus remain non fluorescent and also allow entry of counter stain propidium iodide marking nucleus red. Assay provides rapid quantitative estimation of viability percentage and metabolic vigor as fluorescence intensity correlates with esterase activity and capacity to regenerate wall and divide in culture medium with hormones. Dual staining FDA propidium iodide enables simultaneous live dead discrimination via flow cytometry sorting heterokaryons for somatic hybridization applications.

Ref: Widholm 1972 FDA viability; Larkin 1976 fluorescein diacetate Plant Physiol.

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Animal Tissue Culture 3

The purple color in MTT assay is due to formation of:

Purple color appearing in wells after MTT incubation arises from formation of formazan product 1-(4,5-dimethylthiazol-2-yl)-3,5-diphenylformazan. Enzymatic reduction transfers electrons from succinate via succinate dehydrogenase, NADH and NADPH to tetrazolium ring breaking positively charged quaternary nitrogen and producing neutral formazan with extensive conjugated double bond system delocalizing electrons, absorbing green-yellow wavelengths around 570 nm and appearing purple. Crystals observable microscopically as dark needle-like precipitates clustered around nucleus and in cytoplasm before dissolution. Reaction occurs intracellularly, formazan insoluble in water precipitates. Solubilization with dimethyl sulfoxide disrupts cell membranes releasing formazan into solution yielding purple color intensity proportional to dehydrogenase activity reflecting mitochondrial integrity and overall metabolic fitness. NADH alone yellow, cytochrome c reddish, ATP colorless do not generate purple. Therefore quantification of formazan provides surrogate for viable cell number. Care required as redox-active compounds ascorbic acid and plant polyphenols can directly reduce MTT causing false positive without involving cellular enzymes. Solubilization step must avoid bubbles ensuring accurate absorbance reading and linear correlation with cell number. This knowledge strengthens laboratory safety, protocol reproducibility, and regulatory compliance critical for translational research and clinical applications, ensuring reliable data and workforce protection.

Ref: Berridge et al Arch Biochem Biophys 2005 MTT formazan formation mechanism; Abcam MTT assay protocol formazan purple product succinate dehydrogenase.

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Animal Tissue Culture 3

MTT assay measures:

MTT assay developed by Tim Mosmann in 1983 measures cell viability and proliferation based on reduction capacity of living cells. Principle uses yellow tetrazolium salt 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide which enters cells via endocytosis and is reduced by mitochondrial succinate dehydrogenase of complex II and cytosolic NAD(P)H-dependent oxidoreductases cleaving tetrazolium ring with electrons from NADH and NADPH producing insoluble purple formazan crystals accumulating intracellularly in mitochondria and lipid droplets. Metabolically incompetent dead cells fail to reduce MTT. After incubation 1-4 hours, medium removed and crystals solubilized in dimethyl sulfoxide or acidified isopropanol producing homogeneous purple solution quantified spectrophotometrically at 570 nm with reference 630 nm. Absorbance directly proportional to number of viable cells within linear range. Assay does not measure migration requiring Boyden chamber, DNA synthesis requiring BrdU incorporation, or specific protein expression requiring immunoassay. Applications include cytotoxicity screening, IC50 determination, chemosensitivity testing, and biocompatibility evaluation requiring validation with orthogonal methods. Proper controls including cell-free blanks and vehicle treatments correct for nonspecific dye reduction artifacts. This knowledge strengthens laboratory safety, protocol reproducibility, and regulatory compliance critical for translational research and clinical applications, ensuring reliable data and workforce protection.

Ref: Mosmann T J Immunol Methods 1983 MTT viability assay; ATCC MTT Cell Proliferation Assay mitochondrial dehydrogenase reduction protocol.

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Animal Tissue Culture 3

Cell viability during log phase is approximately:

Exponential log phase represents period of maximal health for mammalian cultures. Under optimal conditions of adequate nutrients, pH maintained at 7.2-7.4 by CO2-bicarbonate buffering, temperature 37°C, and absence of waste accumulation, trypan blue exclusion tests reveal membrane intact viable cells at 90-100% because apoptotic signaling minimal, caspase-3 inactive, mitochondrial membrane potential high as indicated by JC-1 aggregation. Mitochondrial succinate dehydrogenase activity robust leading to efficient reduction of tetrazolium salts in MTT assay. Cells display high cloning efficiency and low spontaneous differentiation. In contrast, lag phase viability slightly lower due to trypsin-induced injury, plateau phase shows gradual decline as contact inhibition triggers quiescence and modest increase in annexin V positivity, and death phase viability drops below 50% with extensive debris. Accurate viability assessment during log phase is crucial before seeding plates for experiments, performing transfections requiring high viability, and virus production where defective particles increase from dying cells. Regular monitoring ensures high-quality inoculum and reproducible experimental outcomes.

Ref: Freshney Ch.18 Viability during log 90-100%; ATCC Cell Viability trypan blue exclusion exponential phase near maximal.

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