Distribution of pectin methyl esterase and acetylesterase in the genus Citrus visualized by tissue prints and chromatography

Abstract

The distribution of pectin methyl esterase (PME) and acetylesterase (AE) in orange, lime, lemon, grapefruit and clementine fruits has been investigated. Isoforms from PME and AE have been separated by cation exchange chromatography. PME isoforms separated in two main groups for all citrus extracts. For AE isoforms, only one major AE isoform was seen in orange, whereas several isoforms were separated in extracts from grapefruit, lime and lemon. The overall localization of AE and PME in the different citrus fruits was investigated by tissue print immunolocalization. In orange, grapefruit and clementine, PME was immunolocalized in the juice vesicles, whereas the PME localization in the juice vesicles was significantly weaker in lemon and lime. The distribution of AE in the juice vesicles differed from the distribution of PME in the sense that PME was more restricted to the periphery of the juice vesicles, whereas AE was also found in the more central parts of the juice vesicles. The immunological detection indicated that PME is involved in the ripening process, but this is probably not the only function for AE. The distribution of AE in paraffin sections of developing lime fruits showed that AE was present in almost all parts of the fruit deposited in the cell wall and intracellularly.