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

Hong-Il Choi,Sang Hoon Kim,Yeong Deuk Jo,Min Jeong Hong,Jin-Baek Kim,Sung Min Han

doi:10.3390/plants10030439

Hong-Il Choi, Sang Hoon Kim + Show 4 more

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https://doi.org/10.3390/plants10030439

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Abstract

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.

Highlights

Ionizing radiation is a primeval stressor from an evolutionary point of view, as all life on Earth has evolved in the presence of various naturally occurring background radiation sources of both cosmic and geologic origin [1]
The amount of DNA damage was higher in acute irradiation treatments than in chronic treatments; neither A-100 nor C-100 showed significant difference compared with the non-irradiated controls (Figure 1)
These results suggest that high dose rates induce stronger damage compared with low dose rates of chronic irradiation

Summary

Introduction

Ionizing radiation is a primeval stressor from an evolutionary point of view, as all life on Earth has evolved in the presence of various naturally occurring background radiation sources of both cosmic and geologic origin [1]. High dose rates cause acute irradiation, whereas low dose rates lead to chronic irradiation [1,5]. Exposure to ionizing radiation causes direct or indirect damage in plants. Direct damage occurs when the radiation energy is transferred to cells and DNA directly, leading to cell damage or cell death and inducing abnormalities [6,7]. Indirect damage is caused by reactive oxygen species (ROS) such as hydroxyl radical (OH), hydrogen peroxide (H2O2), and superoxide anion (O2−), which are generated by water radiolysis and lead to oxidative stress [6,7,8]. DNA damage is known to be induced more by ROS than by direct irradiation [6,9]. Plants employ two kinds of antioxidant machineries: (i) enzymatic machinery comprising antioxidant enzymes such as ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD); and (ii) non-enzymatic machinery, which includes antioxidant metabolites such as ascorbate and glutathione or phytochemicals such as anthocyanins, carotenoids, and phenolic compounds [8,10]

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