ATP-induced changes in energy status and membrane integrity of harvested litchi fruit and its relation to pathogen resistance

Litchi is a subtropical fruit of high commercial value on the international market but the fruit deteriorates rapidly after harvest due to rot development caused by Peronophythora litchii. To investigate the role of energy metabolism during disease development on harvested litchi fruit, fruits were dipped into solutions of either 0 or 1.0 mM adenosine triphosphate (ATP) for 3 min before being inoculated with Peronophythora litchii or not. Fruit were then stored for 6 days at 25 degrees C and 90-100% relative humidity. Significant reductions in pericarp browning and disease severity and significant delays in membrane permeability and malondialdehyde (MDA) content were found in ATP-treated and P. litchii-inoculated fruit. Higher ATP concentrations and adenylate energy charge (EC) were observed in ATP-treated fruit. In addition, lower activities of phospholipase D, acid phosphatase and lipoxygenase enzymes involved in membrane lipid peroxidation and hydrolysis were recorded in ATP-treated fruit. Thus, treatment with ATP maintained higher energy levels, inhibited activities of the membrane hydrolysis-related enzymes, reduced membrane lipid peroxidation and helped maintain membrane integrity of the harvested litchi fruit at the early stage of storage, which could account for the inhibition of disease development of P. litchii-inoculated fruit.