The effect of sucrose on the flower bud opening of ‘Madelon’ cut roses

Complete flower bud opening is characterised by an increase in the petal area, and by enhanced dry and fresh weights of the petals. The import of dry matter into the petals is used for osmotic, biosynthetic and respiratory demands. However, flowers of ‘Madelon’ cut roses frequently fail to open completely under postharvest conditions. An aqueous solution containing 45 mM sucrose induces proper flower bud opening, even when the cut roses have been exposed initially to a sucrose-free solution for 48 h. This points to a requirement for a supply of organic matter from source tissue to the flower as main sink. This conclusion is confirmed by the observation that complete flower bud opening can also be achieved without any addition of sucrose by a reduction in the number of participating petals. Replacing two-thirds part of the 45 mM sucrose by an isomolalic amount of KNO₃ does not affect the flower opening process, implying that a considerable amount of the added sucrose is claimed for osmoregulation. The role of added sucrose and the contribution of the endogenous storage pool in the process of flower bud opening is discussed.