Thus, hexose produced by invertase seemed not to be utilized as an osmoticum but as an energy source or cell wall component. In addition, NAA might have affected not only invertase activities but other physiological activity. Relaxing the cell wall strength for cell enlargement is also important for petal growth. When the cell walls of petals remain rigid, neither water influx nor cell expansion may occur. We previously showed that petal cell wall extensi- bility was also associated with flowering (Yamada et al., 2009b). XTH, which is an enzyme related to cell wall extensibility, was induced by auxin in rice leaf (Cui et al., 2005), and therefore, cell wall extensibility of rose petals also might have been affected by and contributed to accelerated opening of cut flowers treated with NAA.