The effects of gamma irradiation on growth and expression of genes encoding DNA repair-related proteins in Lombardy poplar (Populus nigra var. italica)

In this study, to elucidate the mechanisms of adaptation and tolerance to ionizing radiation in woody plants, we investigated the various biological effects of gamma-rays on the Lombardy poplar (Populus nigra L var. italica Du Roi). We detected abnormal leaf shape and color, fusion, distorted venation, shortened internode, fasciation and increased axillary shoots in gamma-irradiated poplar plants. Acute gamma-irradiation with a dose of 100 Gy greatly reduced the height, stem diameter and biomass of poplar plantlets. After receiving doses of 200 and 300 Gy, all the plantlets stopped growing, and then most of them withered after 4-10 weeks of gamma-irradiation. Comet assays showed that nuclear DNA in suspension-cultured poplar cells had been damaged by gamma-rays. To determine whether DNA repair-related proteins are involved in the response to gamma-rays in Lombardy poplars, we cloned the PnRAD51, PnLIG4, PnKU70, PnXRCC4, PnPCNA and PnOGG1 cDNAs and investigated their mRNA expression. The PnRAD51, PnLIG4, PnKU70, PnXRCC4 and PnPCNA mRNAs were increased by gamma-rays, but the PnOGG1 mRNA was decreased. Moreover, the expression of PnLIG4, PnKU70 and PnRAD51 was also up-regulated by Zeocin known as a DNA cleavage agent. These observations suggest that the morphogenesis, growth and protective gene expression in Lombardy poplars are severely affected by the DNA damage and unknown cellular events caused by gamma-irradiation. (C) 2012 Elsevier Ltd. All rights reserved.