Endogenous free polyamines and their role in fruit set of low and high parthenocarpic ability citrus cultivars.

Endogenous free polyamines (PAs), putrescine, spermidine and spermine, from developing fruitlets of Citrus species (Citrus unshiu Marc. and Citrus clementina Hort ex Tanaka) which differ in their parthenocarpic ability, and from uniflowered leafy and leafless inflorescences differing in their ability to set, have been determined by dansylation and separation of dansyl derivatives by HPLC. No significant differences in PAs content were observed between species or between leafy and leafless inflorescences which, nevertheless, significantly differed in fruit set. However, significant differences in their content were found in developing fruitlets, depending on the preceding flowering intensity of the tree and on the fruitlet load. These results suggest that, in Citrus, PAs may act as a nitrogen source rather than a regulator of fruit set.