Chilling temperature storage changes the inorganic phosphate pool distribution in cherimoya (Annona cherimola) fruit

Abstract

Phophorous nuclear magnetic resonance (31P-NMR) spectroscopy was used to study the vacuolar and cytoplasmic pH and the inorganic phosphate (Pi) pool distribution in 'Fino de Jete' cherimoya (Annona cherimola Mill.) fruit stored at a chilling temperature (6°C). Fruit stored at the ripening temperature (20°C) for 3 days were used as a control. 31P-NMR results confirmed that 6°C storage caused cytoplasmic acidosis (a decrease of 0.72±0.08 pH units) and a notable increase in the amount of Pi in the cytoplasm. Spectra of perchloric acid extracts also revealed that storage at 6°C was associated with an increase in the total amount of Pi and phosphorylated metabolites. Moreover, perfusion experiments with a phosphate medium confirmed the preferential accumulation of Pi in the cytoplasm in chilled tissues. Specific activation of phosphoenolpyruvate carboxylase (PEPC) (32.1±1.7 μmol·min-1·mg-1) was observed in those fruit. In chilled fruit the amount of ADP was held at steady-state levels and ATP levels increased, contrary to observations for ripe fruit, where the pool of total nucleotides decreased beyond the point of NMR detection. Fruit stored at 6°C exhibited a low respiration rate, but metabolism was not arrested and an increase in total soluble solid contents was also observed.