The metabolism of phenolics and reactive oxygen species in relation to the explant browning differences among the varieties of Phalaenopsis during the tissue culture.

The parameters of phenolic and reactive oxygen metabolism were measured in three varieties of Phalaenopsis,i.e.B3,15 and F5 to study the physiological mechanisms of explant browning as well as genotype differences.The total phenol contents of the three varieties were positively correlated with their PAL and POD activities.B3 with the lowest phenol content showed the highest browning degree,PPO activity and MDA content.F5 with highest phenol content had the lowest browning degree,as well as the lowest PPO activity and MDA content.Moreover,SOD and APX activities in F5 were the highest among the three varieties.These results suggested that the browning degree was not directly related to the total phenol content and that explant browning may be due to the phenol oxidation which catalyzed by PPO.Meanwhile,explant browning reflected the membrane damage caused by lipid peroxidation during the tissue culture of Phalaenopsis.The differences in the activities of PPO,SOD and APX possibly might be the main aspects that caused the genotype differences in tissue browning.