GUS activity in onion epidermal cells transformed with the CaMV35S promoter was similar
with or without SA treatment (Figure 6), indicating that the 35S promoter cannot be induced by
exogenous SA. In contrast, GUS activity in cells transformed with P to P5 promoters was higher
after SA treatment than in its absence, indicating that the P to P5 promoters could be induced by
exogenous SA. GUS activity after SA induction was especially high in cells transformed with P2 and
P3. The results suggested that there might be positive regulatory elements within P2 and P3, and
also that there might be negative regulatory elements between the P and P2 sequences.