Gibberellic Acid Inhibits Browning, Enzyme Activity and Gene Expression of Phenylalanine Ammonia-Lyase in Phalaenopsis Leaf Explants

摘要

The effects of gibberellic acid (GA3) on browning, enzyme activity and gene expression of phenylanine ammonia lyase (PAL, EC 4.3.1.5) in Phalaenopsis (Doritaenopsis Queen Bee "Red Sky") leaf explants during tissue culture were investigated. GA_3 at 0(control), 1, 5, 10, 25, 30, 50 and 70 mg L~(-1) were used to treat the explants. The percentage browning and tannin content of explants treated with 25 mg L~(-1) GA_3 were far lower than of control explants cultured for more than 4 days. Paclobutrazol (PBZ), a gibberellin biosynthetic inhibitor, at 5 mg L~(-1), increased the browning percentage, which implied that it was endogenous GA_3 that repressed browning. PAL activity and PAL gene expression were reduced by GA3 treatment but were increased by treatment with PBZ. These results indicate that GA_3 is responsible for the browning of leaf explants through the regulation of PAL gene expression and enzyme activity in Phalaenopsis tissue culture.