Ionizing Radiation, Higher Plants, and Radioprotection: From Acute High Doses to Chronic Low Doses

Abstract

Understanding the effects of ionizing radiation (IR) on plants is important for environmental protection, for agriculture and horticulture, and for space science but plants have significant biological differences to the animals from which much relevant knowledge is derived. The effects of IR on plants are understood best at acute high doses because there have been; (a) controlled experiments in the field using point sources, (b) field studies in the immediate aftermath of nuclear accidents, and (c) controlled laboratory experiments. A compilation of studies of the effects of IR on plants reveals that although there are numerous field studies of the effects of chronic low doses on plants, there are few controlled experiments that used chronic low doses. Using the Bradford-Hill criteria widely used in epidemiological studies we suggest that a new phase of chronic low-level radiation research on plants is desirable if its effects are to be properly elucidated. We emphasize the plant biological contexts that should direct such research. We review previously reported effects from the molecular to community level and, using a plant stress biology context, discuss a variety of acute high- and chronic low-dose data against Derived Consideration Reference Levels (DCRLs) used for environmental protection. We suggest that chronic low-level IR can sometimes have effects at the molecular and cytogenetic level at DCRL dose rates (and perhaps below) but that there are unlikely to be environmentally significant effects at higher levels of biological organization. We conclude that, although current data meets only some of the Bradford-Hill criteria, current DCRLs for plants are very likely to be appropriate at biological scales relevant to environmental protection (and for which they were intended) but that research designed with an appropriate biological context and with more of the Bradford-Hill criteria in mind would strengthen this assertion. We note that the effects of IR have been investigated on only a small proportion of plant species and that research with a wider range of species might improve not only the understanding of the biological effects of radiation but also that of the response of plants to environmental stress.

Towards solving a scientific controversy – The effects of ionising radiation on the environment

“…Recognising the general lack of transgenerational and multigenerational studies and their potential importance in understanding the impacts of long-term exposure in radiologically contaminated environments, some studies focussed on model organisms with well-defined genomes allowing complex genetic/epigenetic analyses. Species studied included Arabidopsis thaliana (Horemans et al, 2018;van de Walle et al, 2016;Caplin and Willey, 2018), Daphnia pulex (Goodman, 2019;Parisot et al, 2015), Danio rerio (Gombeau et al, 2017) and Caenorhabditis elegans (Dutilleul et al, 2015). In addition to existing in-depth knowledge of their genome, the short generation times and relative ease of culturing and maintaining these species was critical to their selection for these challenging long-term effect assessment studies which by their nature involve assessment of effects over parental and subsequent generations.…”

Gene expression in Scots pine populations from the Chernobyl exclusion zone: transcriptomic approach

“…This observation can be understood as another evidence of the adaptation of the evaluated populations to the chronic stress, being the expression of the repair machinery below the detection threshold. Nevertheless, the constant exposure to ionizing radiation imposes a permanent risk for the integrity of the molecules in the cells, including DNA single-and doublestrand breaks (Caplin and Willey, 2018). In this context, our analyses indicate that the strategy adopted by the evaluated populations is to increase the maintenance of the integrity of the molecules in the cell, which could be explained by the enhanced expression of chaperones and histones.…”

Developmental, Morphological and Physiological Traits in Plants Exposed for Five Generations to Chronic Low-Level Ionising Radiation

“…Knowledge of the effects of IR on plants is, however, not just vital for regulating the nuclear industry and responding to nuclear incidents, it is also useful for plant science including agriculture, horticulture and plant stress biology (Caplin and Willey, 2018), space science (Arena et al, 2012;Arena et al, 2019) and to current developments in radiobiology (Kirsch et al, 2018). There has been much significant research into the effects of acute high doses of radiation at a variety of biological levels (e.g., Gicquel et al, 2011;Arena et al, 2017) so they are better understood than those of chronic low doses (Caplin and Willey, 2018). This is, in significant part, because of the widespread use of IR as a physical mutagen in agriculture and horticulture and to sterilize food products (Roberts, 2014).…”

“…The majority of data on the effects of chronic low-level radiation on plants is from radioactively contaminated sites (Caplin and Willey, 2018), primarily those contaminated from nuclear incidents. Field data has particular strengths and weaknesses, and we suggest that this is especially important for studies of exposure to chronic low-level IR.…”