Recovery of embryos of Zizania palustris following exposure to liquid nitrogen

Factors affecting survival of embryos of Zizania palustris after exposure t o liquid nitrogen were investigated. Moisture content was the most critical factor. Embryos desiccated to a moisture content between 0.36 and 0.56 g H 2O/g dry weight had highest survival after liquid nitrogen exposure (56+/-4 % and 52+/-9% respectively). The recovery of embryos in the light following liquid nitrogen exposure also influenced survival. Survival increased from 35+/-4% to 56+/-4% when embryos containing 0.36 g H2O/g dry weight were re covered in the dark compared to light. Embryos exposed to desiccation and f reezing stresses were subject to increased levels of lipid peroxidation. Li ght exacerbated lipid peroxidation in recovering embryos. Furthermore, cata lase and peroxidase, enzymes involved in reducing reactive oxygen species, increased in activity in response to stress, and were further up-regulated in tissues recovered in the light. This study suggests that there are a num ber of factors influencing the survival of tissues exposed to liquid nitrog en and recovery procedures that reduce oxidative stress should be employed.