Abstract
The major carbohydrates in cucumber fruit were reducing sugars, which increased to the highest concentration of about 2.0% of fresh weight at harvest for fresh fruit, that is, 6-8 days after flowering and 73-116g in fresh weight.
Starch was highest in concentration at flowering although it was negligible as compared with sugars.
Reducing sugar concentration was higher in the core (septum and placenta) than in the flesh (receptacle and pericarp). Moreover, it was higher outside than inside the curvature at the curvature increasing stage, while the reverse was true at the curvature decreasing stage.
Labelled carbon was fed to the single leaf on the same node as the fruit. Twenty hours after feeding, 14C-activity was higher in carpel II (outside the curvature and opposite to the tendril) than in carpels I (facing the stem) and III (inside the curvature and facing the tendril) when fed at the curvature increasing stage. When fed at the curvature decreasing stage after the curvature maximum stage had been attained, 14C-activity was higher in carpel III than in carpels I and II.
From these results, it was suggested that the curvature of cucumber fruit occurred due to the competition among the carpels, in uptake of carbohydrates under limited photosynthesis. Each carpel is presumed to be different in sink activity according to its congenital developmental order and stages. Differential carbohydrate translocation due to localization of vascular bundle connections between leaves and fruit is improbable.
