Changes in carbohydrate composition in lettuce flower stalks during development

SummaryChanges in carbohydrate composition in lettuce flower stalks were investigated during growth in order to check whether or not accumulated carbohydrates are used for the rapid development of flower stalks and seed formation. Sucrose was the predominant sugar in lettuce flower stalks, followed by fructans of low molecular weight, glucose and fructose.With regard to fructans, only 1-kestose and 1-nystose were detected, and they increased in concentration from the appearance of terminal flower buds to anthesis. Starch concentration was very low (less than 0.03 mg g–1 dry weight). The concentrations of sucrose, fructans and hexose decreased during seed formation. If fully-developed lettuce leaves were removed from every other node at the flower bud stage, no significant differences were noted in the concentrations of sucrose, glucose, fructose, and fructans in the flower stalks of defoliated and control plants. These results suggest that sucrose and fructans are reserve carbohydrates in stems, and that accumulated sucrose and fructans are used for seed development.