Differentiation between petal blueing and senescence of cut 'Mercedes' rose flowers

One of the striking visible changes that occur in cut red rose flowers duri ng vase life is blueing of the petals prior to wilting. However, it is not clear whether this phenomenon is part of the senescence syndrome. The aim o f this study was to differentiate between petal blueing and sensecence proc esses. For this purpose we followed in parallel the kinetics of several typ ical senescence processes and blueing of rose petals in cut flowers in the presence or absence of sucrose, known to extend the longevity of cut roses and to delay senescence. We have shown that the kinetics of rose petal blue ing is similar to that of the vacuolar pH increase, and different from the kinetics of other senescence parameters such as a decrease in water content and an increase of ion leakage of the petal cells. Sucrose treatment delay ed all the senescence processes assayed at advanced stages, but it had an i mmediate effect only in delaying flower blueing and in increasing cell sap pH. This suggests a correlation between the two processes. Indeed, our resu lts clearly demonstrate that the change in pH occurring in the petals is th e main cause of the blueing effect.