THE BIOCHEMICAL BASIS OF DIFFERENTIAL RIPENING IN MANGO

An inherent characteristic of mango fruit ripening is the occurrence of a differential ripening phenomenon as related to tissue depth. Biochemical indicators associated with cell wall metabolism (i.e. polygalacturonase, -galactosidase activity) and with respiratory metabolism (i.e. NADP-malic enzyme, phosphoenolpyruvate carboxylase, organic acid and sugar levels) suggest that inner mesocarp tissue is metabolically more active than outer mesocarp. Polygalacturonase is differentially distributed, and its activity correlates positively with variation in tissue softness as related to both ripening and tissue position. -Galactosidase and phosphoenolpyruvate carboxylase, too, are differentially distributed, and their activity increases more rapidly in the softer, inner than in the firmer, outer mesocarp. NADP-Malic enzyme activity also registers a faster increase in the inner tissue and this may partly account for a more rapid decline in malate level in that tissue during ripening. As a whole, it appears that flux of respiratory substrates via malate oxidation and also via glycolytic and tricarboxylic acid pathways during ripening is more rapid in inner than in outer mesocarp tissue. The metabolic preponderance of the inner mesocarp suggests that ripening of this climacteric fruit is initiated in the inner tissues, and progresses outwardly.