Sucrose synthesis in Unpollinated ovaries of pomegranate (Punica granatum L.), as well as, in reproductive and vegetative shoot apices

Sugar levels, the enzyme activity of UDP-Glucose Pyrophosphorylase (UGPase) and Sucrose Phosphate Synthase (SPS), key enzymes for sucrose synthesis, and the expression of their respective genes were examined in developing vegetative and reproductive shoot apices and in developing unpollinated ovaries of Pomegranate trees in order to detect differences possibly important for fruit production and plant vigor. The level of total sugars was higher in ovaries, followed by reproductive apices and vegetative apices, suggesting higher energy requirements in the reproductive organs. Moreover, the activities of SPS and UGPase were found to be elevated in the vegetative apices, indicating that sucrose synthesis is possibly differently regulated in comparison to the reproductive organs. Our results suggest that the sink power of each organ primarily regulates the levels of both transported (sucrose, mannitol) and non-transported (fructose, glucose) sugars. However, the endogenous production of sucrose may be a regulatory factor contributing to organ development.