We investigated the expression patterns of diverse genes at various time points after gamma irradiation of young tobacco plants. The first group of genes showed stimulation of transcript levels upon gamma irradiation, although their induction patterns varied. This group included glutathione-S-transferase, peroxidase, superoxide dismutase, and catalase. A second group, with post-irradiation reduction of transcripts, included genes encoding cytosolic ascorbate peroxidase, stromal ascorbate peroxidase, and a TMK1 receptor-like kinase. The third group of genes either showed no change in transcript levels or exhibited irregular patterns. These included genes encoding PR1a (pathogenesis-related protein), tobacco $Ca^{++}$-dependent protein kinase, the $eta$-subunit of translational initiation factor 2B, and CHRK1, a chitinase-related receptor-like kinase. Thus, various genes displayed differential patterns of gene expression in response to gamma irradiation in tobacco plants, thereby suggesting a complex signaling mechanism is involved in the irradiation-induced defense by plants. In addition, many stress-responsive genes exhibited gene expression patterns upon gamma irradiation that differed from those resulting from other biotic and abiotic stresses. With the knowledge of distinctive expression patterns of diverse genes, irradiation-indicating marker plants could be developed by engineering and monitoring multiple radiation-responsive genes.s.