Tetrazolium (TZ) Test

TZ can be used as a stand-alone viability test (not part of a germination test), or used for determining dormancy at the end of a germination test.


Stand-alone TZ Test
Two replicates of 100 seeds are moistened in water over-night.  The next morning the seeds are cut in varying ways to expose critical seed tissues to TZ.

        
Cut seeds                       Cut seeds in TZ Oven     Stained seed

Once the seeds have been cut, they are put into varying concentrations of TZ depending on the species being tested (0.1, 0.5 and 1% are typical concentrations).  The seeds are placed into an oven at 30 to 35 C for several hours, and can be checked for viability.  Staining patterns of the essential seed structures are evaluated.  If the essential structures are healthy tissues and therefore stained, they are considered viable.

Photos of Rocky Mountain Beeplant
         
Essential structures        No structures stained      Only radicle (root)
have stained: Viable       Not viable                        has stained: Not viable


Germination Test (using TZ to determine dormancy)
The methodologies used for stand-alone TZ tests are also used to determine if any remaining firm ungerminated seeds at the end of a germination test are viable.  If any of these are determined to be viable, they are referred to as dormant seeds.  The laboratory always checks for dormancy of native seeds at the end of a germination test.