Soluble carbohydrates in <i>Delphinium</i> and their influence on sepal abscission in cut flowers

Abstract

A carbohydrate other than sucrose, glucose, fructose and myo ‐inositol was detected in sepal extracts of Delphinium . This compound was identified as mannitol by 1 H‐NMR. Mannitol was the major carbohydrate in all examined organs: the sepal, the other parts of the flower, the stem and leaves. Mannitol as well as glucose (both at 0.55 M ), fed to cut Delphinium flowers, similarly delayed the abscission of sepals. 3‐ O ‐methyl glucose (3‐OMG) and polyethylene glycol 200 at the same molar concentrations had no such effect. The treatment with glucose markedly increased the concentrations of glucose and fructose in the sepals without changing the concentrations of sucrose and mannitol. On the other hand, the treatment with mannitol increased the concentrations of glucose and fructose in addition to mannitol in the sepals, suggesting that mannitol is metabolized in Delphinium flowers. The treatment with 3‐OMG increased the concentration of 3‐OMG but not other carbohydrates. Mannitol and glucose similarly delayed the increase in ethylene production in flowers, but 3‐OMG did not. The sensitivity to ethylene was similarly reduced by the treatment with glucose and mannitol, but not by 3‐OMG. These results suggest that the treatment with mannitol, a major carbohydrate in Delphinium , delayed the abscission of sepals by reducing the sensitivity to ethylene. Mannitol further acted, not merely as an osmolyte, but as an apparent source for carbohydrate metabolism in the flower.