Exogenous spermidine delays senescence of Dianthus caryophyllus flowers

Cut carnation flowers, cv. Rieko, were held under standard environmental conditions and treated with different concentrations of spermidine (spd), either by spraying directly on the petals or by supplying it in the water of the vase. The greatest delay of senescence was obtained with 10 mM spd in the water of the vase (10 mM spd-V) while no significant delay of senescence was produced by spraying the flowers. Polyamine levels (free, PCA-soluble and PCA-insoluble conjugated) were determined in control and 10 mM spd-V-treated flowers. Starting from day 3, spermidine was absorbed from the watering solution and accumulated in the petals both in the free and PCA-soluble fractions. Putrescine levels also increased with 10mM spd-V treatment. Total anthocyanin, RNA, DNA, protein content and protease activity were determined over 10 days in control and 10 mM spd-V-supplied flowers. Spermidine was shown to stabilize and retard the degradation of DNA.