Optimization of a working cryopreservation protocol for Pinus patula embryogenic tissue

The protocol currently used to cryopreserve Pinus patula embryogenic tissue was investigated in an attempt to improve and optimize the recovery of tis sue. This: investigation describes two aspects that influence tissue recove ry after cryopreservation: (i) the effects of precooling tissue prior to im mersion into liquid nitrogen: and (ii) whether the choice of supports onto which the recovered tissue is suspended improved the recovery rate. Results indicated that precooling tissue to -70 degreesC prior to immersion into l iquid nitrogen was superior to precooling to -30 degreesC or direct immersi on in liquid nitrogen (-196 degreesC). Tissue recovery improved when polyes ter grids were used as supports, and was slowest on filter paper supports.