Activities of glycosidases during fruit development and ripening of tomato (Lycopersicum esculantum L.): implication in fruit ripening

摘要

Glycosidases such as beta-hexosaminidase, (alpha-mannosidase and alpha-galactosidase are believed to play a major role in textural softening during fruit ripening. The activities of beta-hexosaminidase and (alpha-galactosidase, which were low initially during fruit development, significantly increased during ripening in tomato. On the other hand, activity of (alpha-mannosidase, which increased during fruit development, steadily increased further during ripening after a transient decrease. The specific activity of beta-hexosaminidase and alpha-mannosidase in tomato extracts considerably decreased upon dialysis. Protein profiles on SDS-PAGE showed differences in the presence of protein bands between fruit developmental and ripening stages. The carbohydrate/protein ratio increased from fruit developmental to ripening stage with a highest value at the climacteric stage, suggesting active synthesis of glycoproteins. All the three alpha-mannosidase isoforms in tomato were found to have a common subunit having a molecular mass of 55 kDa, while isoform-II and -III were found to have an additional subunit of molecular mass 36 kDa. Antibody raised against bell capsicum alpha-mannosidase also cross-reacted with tomato (alpha-mannosidase. The intensity of cross-reaction increased towards ripening stage of the fruit from developmental stage, showing ripening specificity of this enzyme in tomato fruits. Immuno-diffusion study with tomato tissue blotting also supported this inference