that act downstream from phospholipase D. for the phospholipids. Thus, phosphatidatephos phatase, lipolytic acyl hydrolase, and lipoxygenase do not directly act on phospholipids, though there are exceptions to this rule. Therefore the degree of membrane lipid catabolism will be determined by the extent of activation of phospholipase D The membrane lipid catabolic pathway is considered as an autocatalytic pathway. The destabilization of the membrane can cause the leakage of calcium and hydrogen ions from the cell wall space, as well as the inhibition of calcium and proton ATPases, the enzymes responsible for maintaining a physiological calcium and proton concentration within the cytoplasm (calcium concentration below micromolar range, pH in the 6 6.5 range). Under conditions of normal growth and development, these enzymes pump the extra calcium and hydrogen ions that enter the cytoplasm from storage areas such as apoplast and the ER lumen, in response to hormonal and environmental stimulation using ATP as the energy source. The activities of calcium and proton ATPases localized on plasma membrane, endoplasmic reticulum, and the tonoplast are responsible for pumping the ions back into the and storage areas. In fruits (and other senescing systems), with the advancement in ripening senescence, there is a progressive increase in leakage of calcium and hydrogen ions. Phos pholipase D is stimulated by low pH and calcium concentration over 10 M. Thus, if the cytosolic concentrations of these ions progressively increase during ripening or senescence he membranes are damaged as a consequence. However, this is an inherent feature of the ripening process in fruits, which results in the development of ideal organoleptic qualities makes them edible. The uncontrolled membrane deterioration can result in the loss of shelf life and quality in fruits