Physiological and biochemical basis of internal breakdown in Alphonso mango-a study on the roles of ethylene, calcium and oxidative stress

Abstract

Reduction in ethylene evolution in the spongy tissue was mainly due to the reduced activity of ACC oxidase leading to the accumulation of ACC. This might have lead to the reduced ripening of the tissues resulting in sponginess. There are many softening enzymes and the major ones are polygalacturonase, pectin methyl esterase and cellulase. Results indicated the lower softening of the tissues in the spongy tissue when compared to the healthy tissues. In climacteric fruits like mango respiratory raise during ripening is very important for proper ripening and development of good aroma. The ethylene hormone strictly controls this. In this direction an attempt has been made to assess the respiratory enzymes to understand whether they are affected due to the formation of spongy tissue. Activities of starch and sugar metabolising enzymes are decreased in spongy tissue leading to the lower sugar formation. Study of antioxidative enzymes in spongy tissues. Oxidative free radicals have been associated with many membrane related disorders. Lipid peroxidation is one of the important effects of free radicals damage. Oxidative free radicals combined with metallic ions like ferrous results in greater damage due to the production of highly reactive hydroxyl radicals. Free radicals are usually scavenged by the antioxidative enzymes like SOD, catalyse, peroxidase, polyphenol oxidase, ascorbate peroxidase, glutathione reductase etc.,. However, if there is damage to the free radical scavenging mechanism then there will be an accumulation in free radicals resulting in the damage of membrane. As a measure of oxidation products MDA has been analysed and antioxidative enzymes like super oxide dismutase, peroxidase, catalyse, polyphenopl oxidase have been estimated in different samples. Spongy tissue has higher oxidative products and lower activity of antioxidative enzymes indicating the lipid peroxidation of membranes. Minerals are essential for the normal functioning of membranes and also for the maintenance of turgor of the cells and for enzyme activities. In this regard, minerals like Zn, Fe, Ca and Mg are estimated in spongy and healthy tissues. Most of the minerals except Ca did not show any significant differences between the tissues. Calcium showed a marginal reduction in spongy tissue.