**2.2.6.3 Tetrazolium test for viability**

Shoot tips which were pretreated with high sucrose concentrations; pretreated and cryoprotected with MPVS2; pretreated, cryoprotected, and vitrified, were cultured on growth medium for 5-7 d following which they were transferred to a 0.1% aqueous solution of 2,3,5-triphenyl tetrazolium chloride (TTZ) and incubated in the dark overnight. Control material was obtained from cultures under standard growth room conditions. Patchy red staining, located around the meristematic region as a result of respiratory activity in viable cells was scored as the tissue having survived the various treatments.
