Effects of Acute and Chronic Heavy Metal Chromium Stress on Heat Shock Protein Gene and Antioxidant Enzyme Activities of Orthetrum Albistylum Larvae

Abstract

The dragonfly, Orthetrum albistylum, can accumulate heavy metals from its aquatic environment, thus serving as a biological indicator for monitoring and evaluating water quality. Heat shock proteins (HSPs) play important biological roles in resisting various types of environmental stress. Thus, full-length cDNA sequences of heat shock cognate (hsc) 70 and heat shock protein (hsp) 70 genes were cloned from O. albistylum larvae. The relative expression levels of hsc70 and hsp70 genes in head, epidermis, midgut and adipose body were detected. Chronic and acute infection of 5~8 instar larvae with Chromium (Cr) solution. The relative expression levels of hsc70 and hsp70 genes in chronic and acute infected larvae were measured by qRT-PCR, and the activities of superoxide dismutase (SOD) and catalase (CAT) in the chronically infected larvae were measured. Phylogenetic analysis results revealed that the cloned hsc70 and hsp70 were highly homologous with known HSP70 family members reported in other insects. mRNA levels of hsc70 and hsp70 did not differ significantly in various larval tissues but were the highest in the midgut. Under chronic chromium stress, hsc70 and hsp70 expression was upregulated to the maximum and then downregulated; hsp70 mRNA levels were higher than those of hsc70 for all chromium concentrations. Under acute chromium stress, hsc70 expression was inhibited at low concentrations and upregulated at chromium concentrations > 125 mg/L. However, hsp70 expression was higher than that in the control group and markedly higher than that of hsc70. Changes in SOD and CAT activities displayed consistent trends for different chronic chromium concentrations, first increasing and then decreasing over time. Collectively, these findings elucidated the response of HSP family and antioxidant enzymes to heavy metal stress as well as their potential applicability as biomarkers for monitoring environmental pollutants.

Keywords: Orthetrum albistylum, chromium, heat shock cognate 70, heat shock protein 70, anti-oxidant enzymes