Liquid-nitrogen homogenization

CELL WALLS AND SECONDARY PRODUCTS AS OBSTACLES TO PLANT ENZYME ISOLATION PROBLEMS AND SOLUTIONS, INCLUDING A SIMPLE LIQUID-NITROGEN HOMOGENIZER FOR BULK TISSUE EXTRACTION ... 

The sample is put in a 4He cryostat and enclosed by a shield thermally connected to the liquid helium reservoir. A second thermal shield connected to a liquid nitrogen reservoir encloses all the liquid helium system, allowing for a slow warming-up cycle in order to ensure thermal homogeneity of sample and holder. A window in the dewar enables the laser beam to enter the chamber and to reach the sample through small bores in both thermal shields. The sample is fixed onto a copper support that is in good thermal contact... 

The master cell bank is a homogeneous suspension of the original cells already transformed by the expression vector containing the desired gene, distributed in equal volumes into individual containers for storage (e.g. in liquid nitrogen). In some cases it may be necessary to establish separate master cell banks for the expression vector and the host cells. 

The time needed for homogenization varies based on the nature of the sample. For some hard-to-break samples, pretreatment with liquid nitrogen and pulverization will help. 

---