Low O2-induced changes in pH and energy charge in pear fruit tissue

Abstract

Pear (Pyrus communis L. cv. 'Bartlett') fruit were stored at 0°C for 2 or 4 weeks and subsequently ripened in air at 20°C or treated for 4 days with 0.25% 0 2 at 20°C before transfer to air for ripening. The juice pH (indicator of vacuolar pH) of air-treated fruit decreased slightly with ripening. Exposure to 0.25% 0 2 resulted in higher juice pH during the treatment and after transfer to air. Pear fruit discs, after 10 h aging, were also kept in air or 0.25% 02 at 20°C for 2 days and their 31p-NMR spectra obtained. The 0.25% O2-treated discs had higher cytoplasmic Pi (relative to the vacuolar Pi), had about 0.4 pH units lower cytosolic pH and lower ATP/ADP ratio indicating lower energy charge. The above changes could alter the in vivo activity of a number of respiratory enzymes in fruit subjected to hypoxic treatment.