Abstract: To test the hypothesis that oxidative stress is involved in inducing freezing injury of plants,nitroblue tetrazolium (NBT) was infiltrated into cabbage leaf tissues before they were frozen. NBTwas reduced to formazans in freeze thaw cycles. The ethanol-extractable mono-formazan was measured by a spectrophotometer,and used as a quantitative indicator of oxidative stress that developed during a freeze-thaw cycle. NBT perse as an oxidant increased the freezing injury slightly. When Me₂SO as a cryoprotectant was infiltrated into leaf tissue,it apparently enhanced the freezing tolerance,and this is correlated to its ability in ameliorating oxidative stress,as indicated by the partial inhibition of NBTreduction.The results supported the hypothesis that freezing injury of plants is related to oxidative stress. The experiments indicated that it was possible that the reductant of NBTin the freeze thaw cycle was superoxide anion free radical.

Key words: Oxidative stress, Freezing injury, NBT reduction, Cabbage, reconstruction, tree ring width, climate change, NDVI, Larix chinensis