Metallothionein expression induced by nickel accumulation in the midgut of Spodoptera litura Fabricius larvae exposed to nickel

Abstract

Metallothionein expression induced by nickel accumulation in the midgut of Spodoptera litura Fabricius larvae was investigated by exposing S. litura larvae to the artificial diets amended with different doses of nickel for 3 generations. Nickel accumulations in the midgut of 6th instar larvae were detected by Inductively Coupled Plasma-Atomic Emission Spectrometer (ICP-AES), and the induced metallothionein expression in the midgut of 5th and 6th instar larvae in 120 h were quantified using cadmium-hemoglobin total saturation methods. The accumulated nickel in the midgut of the 6th instar larvae within a generation increased with the increase of the nickel doses in the treated diets and showed significant dose-dependence with the nickel doses in diets. Metallothioneins induced by nickel accumulated in the larval midgut also increased with nickel doses in diets and with the increasing stressing time in a generation. Results also suggested that the metallothionein expression was different with the time of S. litura larvae stressed by nickel.nickel, Spodoptera litura, midgut, accumulation, metallothionein Metallothionein (MT) is a family of ubiquitous cysteine-rich protein binding heavy metals with a low molecular weight. Apart from the role of MTs in trace element storage, transportation and metabolism, MTs are also involved in a number of biological processes, such as protection against ionizing radiation and oxidative damage caused by free radical, especially in the processes of heavy metal detoxification and tolerance [1] . MT expression in different tissues could be induced by exposing organisms to the polluted environment by heavy metals.Nickel is one of the heavy metals that induce some animals to express MT. For example, MT concentrations in the kidneys of Coregonus clupeaformis (Mitchill) and Salvelinus namaycush (Walbaum) significantly increased with feeding diets containing excessive nickel [2] . Perca flavescens (Mitchill) also increases MT amount against the oxidation induced by nickel accumulation in the animal [3] .There were a few reports concerning the effects of heavy metals on the MT expression in insects. It was found that MT could be induced by some heavy metals, such as Cu, Zn, Cd and Pb in some insects of Collembulous Orchesella cincta (L.), Dipterous Drosophila melanogaster (L.), Musca domestica (L.) and Boettcherisca peregrina (Robineau-Desvoidy) [4] . High level MT expression was induced by Cd, Cu and Zn stress in the larvae of Culex quinquefasciatus (Say), and by Cd stress in the larvae of O. cincta [5,6] . The tolerance of D. melanogaster to Cu and Cd was apparently correlated with replication of MT gene [7] . Though MT gene of Bombyx mori (L.) was expressed in E. coli by random clone [8] , there were no reports concerning the impacts of

Effects of dietary nickel on detoxification enzyme activities in the midgut of Spodoptera litura Fabricius larvae

“…It was also proposed that GSH is capable of chelating metals soon after they enter into the cells, and transferring the metals to the metal-binding site of MT [23] . In our previous studies, heavy metal nickel was found to be able to accumulate in the midgut of the 6th instar larvae of Spodoptera litura Fabricius exposed to different doses of nickel for 3 generations [24] . Furthermore, MT increased with the increasing nickel doses in diets and the stressing time in one generation [24] .…”

“…In our previous studies, heavy metal nickel was found to be able to accumulate in the midgut of the 6th instar larvae of Spodoptera litura Fabricius exposed to different doses of nickel for 3 generations [24] . Furthermore, MT increased with the increasing nickel doses in diets and the stressing time in one generation [24] . However, the trends of detoxification enzymes CarE and GST in midgut of S. litura larvae stressed by nickel, and the relationships between enzyme activities and MT levels in midgut were unknown.…”