Gene expression profiling reveals decreased expression of two hemoglobin genes associated with increased consumption of oxygen in Chironomus tentans exposed to atrazine: A possible mechanism for adapting to oxygen deficiency

Atrazine is an extensively used triazine herbicide in agricultural and residential areas and has been routinely detected in many surface and ground waters. This study reveals various up- and down-regulated genes associated with hypoxic stress in atrazine-treated fourth-instar Chironomus tentans larvae (midges) by using restriction fragment differential display-PCR. Two down-regulated hemoglobin cDNAs were isolated from the midges. Northern blot analysis indicated CteHb-IIβ and CteHb-III mRNA expressions decreased by 36 and 21%, respectively, in midges exposed to atrazine at 1 μg/L for 96 h. Decreased hemoglobin gene expression was associated with elevated oxygen consumption in atrazine-treated midges. Midges exposed to atrazine at 1 μg/L increased their oxygen consumption by 47%, whereas midges exposed to atrazine at 1000 μg/L for 48 h increased their oxygen consumption by 66%. Our study demonstrates for the first time that atrazine, at environmentally relevant concentrations, can elevate respiration, possibly eliciting counteractive measures at the transcriptional level to adapt to oxygen deficiency in an ecologically important aquatic insect. Our results further suggest that the ability to modulate both the quantity and quality of Hb serves as an adaptive response to counteract the initial onset of oxygen deficiency induced by atrazine in midges.