Chronic effect of cadmium on phosphatase activity in the midgut of gypsy moth larvae

Abstract

Chronic effects of two cadmium concentrations (10 and 30 µg Cd/g dry food) on larval mass and midgut phosphatase activity (total, acid lysosomal and alkaline), were investigated in the 4th instar of the gypsy moth larvae (Lymantria dispar L.). Native PAGE was used for detection of phosphatases isozymes using p-nitrophenyl phosphate as a substrate. The analysis was performed on 20 egg masses (5 larvae/ egg mass/ treatment). It was found that both cadmium concentrations had inhibitory effect on phosphatase activity (total, lysosomal and alkaline). Only higher concentration (30 µg Cd/g dry food) reduced larval mass. Electrophoretograms of acid and alkaline phosphatases showed three major isoforms which differed in the level of expression depending on egg mass and cadmium treatment. Variability of alkaline phosphatase at 10 µg Cd/g dry food was lower than at the control treatment, while variance of lysosomal phosphatase was significantly higher at 30 µg Cd/g compared to control. As midgut homogenates were pulled within each egg mass (full-sib family), the change in a trait variance represented the change in genetic diversity. Significant and positive correlations for alkaline phosphatase between control and two cadmium concentrations as well as between the two cadmium treatments showed common genetic determination of a trait in the suitable and stressful environment. Common genetic determination was also observed between two cadmium concentrations for larval mass. The absence of significant correlations for lysosomal phosphatase between different environments might point to expression of different genes. Decrease of lysosomal phosphatase activity at both cadmium concentrations, increase of variance at 30 µg Cd/g and lack of significant correlations between different treatments indicate that this enzyme could be indicator of environmental changes.