In plants, there are issues related to the effects of gamma (γ)-rays that are still poorly explored, particularly as concerns the biological response to irradiation delivered at a low dose rate. In the present work, the effects of exposure to increasing γ-ray total doses (6, 12, 25, and 50 Gy) delivered at 0.29 Gy min-1, were evaluated in terms of DNA damage sensing and repair in Medicago truncatula proliferating cell suspension cultures. The profiles of reactive oxygen species (ROS) and nitric oxide (NO) production, monitored by fluorescent staining, were in agreement with the transcriptional response of genes encoding the respiratory burst oxidase-like protein C (MtRBOHC), nitrite reductase (MtNR)... More
In plants, there are issues related to the effects of gamma (γ)-rays that are still poorly explored, particularly as concerns the biological response to irradiation delivered at a low dose rate. In the present work, the effects of exposure to increasing γ-ray total doses (6, 12, 25, and 50 Gy) delivered at 0.29 Gy min-1, were evaluated in terms of DNA damage sensing and repair in Medicago truncatula proliferating cell suspension cultures. The profiles of reactive oxygen species (ROS) and nitric oxide (NO) production, monitored by fluorescent staining, were in agreement with the transcriptional response of genes encoding the respiratory burst oxidase-like protein C (MtRBOHC), nitrite reductase (MtNR), the cytosolic isoform of ascorbate peroxidase (MtAPX), and a type 2 metallothionein (MtMT2). The genotoxic effects were assessed using the alkaline and neutral version of single cell gel electrophoresis (SCGE), detecting the occurrence of SSBs and DSBs. Independent on the irradiation dose, M. truncatula cells always revealed the preferential repair of DSBs, while the SSB repair was less effective. The DNA repair response was investigated focusing on genes representative of different DNA repair pathways. The overall picture derived from gene profiling analysis highlights that M. truncatula cells can produce an active response to IR-mediated genotoxic stress, as indicated by the up-regulation of the DSB sensor MtMRE11 gene, the MtTop2 gene, and the MtOGG1gene, an essential component of the base excision repair pathway. In contrast, the MtTop1, MtTdp1 and MtTFIIS genes, believed to be part of the nucleotide excision repair pathway, were significantly down-regulated.
