Sublethal gamma irradiation affects reproductive impairment andelevates antioxidant enzyme and DNA repair activities in themonogonont rotifer Brachionus koreanus

Abstract

To examine the effects of gamma radiation on marine organisms, we irradiated several doses of gammaray to the microzooplankton Brachionus koreanus, and measured in vivo and in vitro endpoints includingthe survival rate, lifespan, fecundity, population growth, gamma ray-induced oxidative stress, and mod-ulated patterns of enzyme activities and gene expressions after DNA damage. After gamma radiation,no individuals showed any mortality within 96 h even at a high intensity (1200 Gy). However, a reducedfecundity (e.g. cumulated number of offspring) of B. koreanus at over 150 Gy was observed along with aslight decrease in lifespan. At 150 Gy and 200 Gy, the reduced fecundity of the rotifers led to a significantdecrease in population growth, although in the second generation the population growth pattern wasnot affected even at 200 Gy when compared to the control group. At sub-lethal doses, reactive oxygenspecies (ROS) levels dose-dependently increased with GST enzyme activity. In addition, up-regulationsof the antioxidant and chaperoning genes in response to gamma radiation were able to recover cellulardamages, and life table parameters were significantly influenced, particularly with regard to fecundity.DNA repair-associated genes showed significantly up-regulated expression patterns in response to sub-lethal doses (150 and 200 Gy), as shown in the expression of the gamma-irradiated B. koreanus p53 gene,suggesting that these sublethal doses were not significantly fatal to B. koreanus but induced DNA damagesleading to a decrease of the population size.