Tonoplast Lipid Composition and Proton Pump of Pineapple Fruit During Low-Temperature Storage and Blackheart Development

Vacuole represents a major storage organelle playing vital roles in pH homoeostasis and cellular detoxification. The chemical and functional properties of tonoplast in response to chilling temperature and their roles in chilling injury are largely unknown. In the current study, lipid composition of tonoplast and the activities of two vacuolar proton pumps, H+-ATPase (V-ATPase) and H+-pyrophosphatase (V-PPase), were investigated in accordance with the development of blackheart, a form of chilling injury in pineapple fruit (Ananas comosus). Chilling temperature at 10 A degrees C for 1 week induced irreversible blackheart injury in concurrence with a substantial decrease in V-ATPase activity. By contrast, the activity was increased after 1 week at 25 A degrees C. The activity of V-PPase was not changed under both temperatures. Level of total phospholipids of tonoplast decreased at 10 A degrees C, but increased at 25 A degrees C. There was no change at the level of total glycolipids under both temperatures. Thus, low temperature increased the ratio of total glycolipids vs. total phospholipids of tonoplast. Phosphatidylcholine and phosphatidylethanolamine were the predominant phospholipids of tonoplast. Low temperature increased the relative level of phosphatidic acid but decreased the percentage of both phosphatidylcholine and phosphatidylethanolamine. Unsaturated fatty acids accounted for over 60 % of the total tonoplast fatty acids, with C18:1 and C18:2 being predominant. Low temperature significantly decreased the percentage of C18:3. Modification of membrane lipid composition and its effect on the functional property of tonoplast at low temperature were discussed in correlation with their roles in the development of chilling injury in pineapple fruit.