There are two PAL genes in lettuce. After cutting, expression of both PAL1 and PAL2 genes were rapidly increased in controls within
2 h, reached a peak at 6 h, and then decreased quickly to the basal level by 50 h (Fig. 2). However, the expression levels of the two PALs in ethanol treated discs were significantly reduced as compared to controls. In particular, PAL2 expression was hardly detected in ethanol treated discs. Although we detected an expression peak of PAL1 at 12 h after ethanol treatment, its expression level was only about half of that observed in the control group. These results indicated that ethanol immersion can quickly repress the expres- sion of both PALs in lettuce stem after cutting.
Further we investigated whether the PAL activity was affected by ethanol treatment. The PAL activity in the control group after cutting increased very rapidly, peaked within two days and then decreased (Fig. 3). However, in treated samples the PAL activity rose gradually until the 3rd day and then leveled off at around
0.6 mol kg 1 FW h 1. The largest difference occurred on the 2nd
day, when the PAL activity in the ethanol treated samples was only about 10% of the untreated control. After the 3rd day, the PAL ac- tivity in the treated samples and untreated controls became closer, although it remained higher in the control. Altogether these results indicated that cutting/wounding stimulated PAL gene expression and activity. However, the ethanol treatment can effectively repress the PAL gene expression and reduce PAL activity