Effects of Acute and Chronic Gamma Irradiation on the Cell Biology and Physiology of Rice Plants

The response to gamma irradiation varies among plant species and is affected by the total irradiation dose and dose rate. In this study, we examined the immediate and ensuing responses to acute and chronic gamma irradiation in rice (Oryza sativa L.). Rice plants at the tillering stage were exposed to gamma rays for 8 h (acute irradiation) or 10 days (chronic irradiation), with a total irradiation dose of 100, 200, or 300 Gy. Plants exposed to gamma irradiation were then analyzed for DNA damage, oxidative stress indicators including free radical content and lipid peroxidation, radical scavenging, and antioxidant activity. The results showed that all stress indices increased immediately after exposure to both acute and chronic irradiation in a dose-dependent manner, and acute irradiation had a greater effect on plants than chronic irradiation. The photosynthetic efficiency and growth of plants measured at 10, 20, and 30 days post-irradiation decreased in irradiated plants, i.e., these two parameters were more severely affected by acute irradiation than by chronic irradiation. In contrast, acutely irradiated plants produced seeds with dramatically decreased fertility rate, and chronically irradiated plants failed to produce fertile seeds, i.e., reproduction was more severely affected by chronic irradiation than by acute irradiation. Overall, our findings suggest that acute gamma irradiation causes instantaneous and greater damage to plant physiology, whereas chronic gamma irradiation causes long-term damage, leading to reproductive failure.

Formation of γH2AX and pATM Foci in Human Mesenchymal Stem Cells Exposed to Low Dose-Rate Gamma-Radiation

DNA double-strand breaks (DSB) are among the most harmful DNA lesions induced by ionizing radiation (IR). Although the induction and repair of radiation-induced DSB is well studied for acute irradiation, responses to DSB produced by chronic IR exposures are poorly understood, especially in human stem cells. The aim of this study was to examine the formation of DSB markers (γH2AX and phosphorylated kinase ATM, pATM, foci) in human mesenchymal stem cells (MSCs) exposed to chronic gamma-radiation (0.1 mGy/min) in comparison with acute irradiation (30 mGy/min) at cumulative doses of 30, 100, 160, 240 and 300 mGy. A linear dose-dependent increase in the number of both γH2AX and pATM foci, as well as co-localized γH2AX/pATM foci (“true” DSB), were observed after an acute radiation exposure. In contrast, the response of MSCs to a chronic low dose-rate IR exposure deviated from linearity towards a threshold model, for γH2AX, pATM foci and γH2AX/pATM foci, with an indication of a “plateau”. The state of equilibrium between newly formed DSB at a low rate during the protracted exposure time and the elimination of a fraction of DSB is proposed as a mechanistic explanation of the non-linear DSB responses following a low dose-rate irradiation. This notion is supported by the observation of the elimination of a substantial fraction of DSB 6 h after the cessation of the exposures. Our results demonstrate non-linear dose responses for γH2AX and pATM foci in human MSCs exposed to low dose-rate IR and showed the existence of a threshold, which may have implications for radiation protection in humans.

Induksi Mutasi Fisik pada Paku Bintik (Microsorum punctatum) melalui Iradiasi Sinar Gamma

Pemuliaan mutasi dengan iradiasi sinar gamma merupakan salah satu cara dalam meningkatkan keragaman genetik tanaman. Tujuan penelitian ini adalah mengetahui radiosensitivitas dan nilai LD₅₀ (<em>Lethal dose</em> 50) sinar gamma pada <em>M. punctatum </em>serta mengamati keragaan tanaman <em>M. punctatum</em> hasil iradiasi sinar gamma pada MV1. Nilai LD₅₀merupakan salah satu parameter untuk mengukur tingkat sensitivitas suatu jaringan terhadap iradiasi. Semakin rendah nilai LD₅₀ suatu jaringan tanaman, semakin tinggi tingkat radiosensitivitasnya, sehingga semakin besar peluang terjadinya mutasi. Penelitian ini menggunakan rancangan acak lengkap (RAL) faktor tunggal (dosis iradiasi sinar gamma) dengan 3 ulangan. Iradiasi sinar gamma diberikan terhadap stek rimpang dengan satu daun dari tanaman <em>M. punctatum</em> secara tunggal (<em>acute irradiation</em>) menggunakan <em>Gamma Cell </em>220 dengan dosis 0, 10, 20, 30, 40, dan 50 gray. Semua rimpang dengan satu daun hasil iradiasi ditanam di lapangan hingga 16 minggu setelah iradiasi (MSI). Hasil penelitian menunjukkan bahwa pemberian iradiasi sinar gamma pada <em>M. punctatum</em> menghasilkan LD₅₀sebesar 86,25 gray dan perlakuan iradiasi sinar gamma antar perlakuan berbeda nyata terhadap tinggi dan lebar daun, sedangkan karakter jumlah daun tidak berbeda nyata<em>.</em> Perlakuan iradiasi juga menyebabkan defisiensi warna hijau pada daun <em>M. punctatum</em>. Secara morfologi, perlakuan iradiasi sinar gamma terhadap <em>M. punctatum</em> belum menghasilkan mutan-mutan yang diinginkan, namun secara genetik, terdapat penggandaan jumlah kromosom dan aberasi kromosom pada perlakuan dosis iradiasi tertinggi (50 gray).

Induksi Mutasi Fisik pada Paku Bintik (Microsorum punctatum) melalui Iradiasi Sinar Gamma

Pemuliaan mutasi dengan iradiasi sinar gamma merupakan salah satu cara dalam meningkatkan keragaman genetik tanaman. Tujuan penelitian ini adalah mengetahui radiosensitivitas dan nilai LD50 (Lethal dose 50) sinar gamma pada M. punctatum serta mengamati keragaan tanaman M. punctatum hasil iradiasi sinar gamma pada MV1. Nilai LD50 merupakan salah satu parameter untuk mengukur tingkat sensitivitas suatu jaringan terhadap iradiasi. Semakin rendah nilai LD50 suatu jaringan tanaman, semakin tinggi tingkat radiosensitivitasnya, sehingga semakin besar peluang terjadinya mutasi. Penelitian ini menggunakan rancangan acak lengkap (RAL) faktor tunggal (dosis iradiasi sinar gamma) dengan 3 ulangan. Iradiasi sinar gamma diberikan terhadap stek rimpang dengan satu daun dari tanaman M. punctatum secara tunggal (acute irradiation) menggunakan Gamma Cell 220 dengan dosis 0, 10, 20, 30, 40, dan 50 gray. Semua rimpang dengan satu daun hasil iradiasi ditanam di lapangan hingga 16 minggu setelah iradiasi (MSI). Hasil penelitian menunjukkan bahwa pemberian iradiasi sinar gamma pada M. punctatum menghasilkan LD50 sebesar 86,25 gray dan perlakuan iradiasi sinar gamma antar perlakuan berbeda nyata terhadap tinggi dan lebar daun, sedangkan karakter jumlah daun tidak berbeda nyata. Perlakuan iradiasi juga menyebabkan defisiensi warna hijau pada daun M. punctatum. Secara morfologi, perlakuan iradiasi sinar gamma terhadap M. punctatum belum menghasilkan mutan-mutan yang diinginkan, namun secara genetik, terdapat penggandaan jumlah kromosom dan aberasi kromosom pada perlakuan dosis iradiasi tertinggi (50 gray).