Keywords

1 Introduction

In the contemporary era, mankind is surrounded by a network of natural and non-natural radiation globally which is continually increasing. According to the energy, there are two types of radiation, i.e., ionizing and nonionizing. The sensitivity to radiation has got a great deal of concern in the last decades because many electromagnetic devices were invented and introduced (Guleria et al. 2019). Ionizing radiation possesses enough energy to break down molecular bonds and transfer electrons from atoms, thereby considered as more damaging to the well-being of the organisms. Ionizing radiations have several harmful effects on human health. The rapid development of technology has greatly increased people’s exposure to ionizing radiations; thus, protecting humans from the detrimental impacts of ionizing radiations is a need of hour (Jagetia 2007). Radioprotective agents or anti-radioactive substances are those that can reduce the negative effects of radiation in healthy tissues while retaining the sensitivity to radiation damage in cancerous cells (Painuli and Kumar 2016). Radiation can be defined as the energy released in the form of electromagnetic waves or particles from radioactive material (Lindell and Favaro 2013). In particular, the demand for harmful ionizing radiation is constantly increasing due to expeditious advancement in their use in radiography, nuclear science, space flights, and other modern technologies. Thereby, there is an urgent need to protect plants, animals, and humans from radiation. Exposure to ionizing radiation may cause detrimental consequences to various organs and systems viz., eyes, skin, thyroid glands, stomach, guts, lungs, and reproductive blood systems, which can cause numerous pathophysiological disorders (Fig. 1). Though all materials absorb radiations to some extent, nevertheless some are better than others to absorb specific electromagnetic radiation frequencies. For example, glass absorbs from opaque to infrared radiations (Li et al. 2014), charcoal absorbs from opaque to visible light, while high-energy radiations (like X-rays) can be absorbed by denser materials such as lead (Rebois and Ray 2012). The air, on the other hand, absorbs almost all the radiation coming from space. Future research should focus on understanding the mechanistic role of different types of radiation in our daily life to reduce their impacts on human health without using an electronic instrument, which has high effects on radiations (Durante and Cucinotta 2011). In this regard, plants are the most suitable and economical source to absorb the harmful radiation in the air and mitigate the impacts of air pollution and climate change on human health. The most practical way is the identification and selection of viable candidates along with their evaluation for radioprotection (Jagetia 2007; Ayyanar and Subash-Babu 2012). After the critical evaluation of the anti-inflammatory, antioxidant, antimicrobial, immunomodulatory, free radical scavenging, or anti-stress properties of a substance that can be considered as a potential radioprotective agent (Jagetia and Baliga 2003). With this background, the work is designed to provide the basics of radiation exposure-mediated consequences in humans along with the radioprotection potential of various plants. Moreover, this chapter is an outcome of an extensive literature survey, so authors have tried to provide a clear image plus gaps in this particular area which is still scarce.

Fig. 1
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Sources of ionizing radiations and their adverse impacts on the human body

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2 Mechanisms of Radiation Damage

Ionizing radiations damage various cells, tissues, and organs through a cascade of molecular events often triggered by free radicals known as reactive oxygen species (ROS) (Mates 2000). Exposure to radiation leads to DNA damage in terms of base damage, single-strand breaks (SSBs) or double-strand breaks (DSBs), DNA–DNA or protein crosslinks, which is ultimately responsible for altered genomic expression, cell death, protein modification, genomic instability, and senescence (Devasagayam et al. 2004). Genomic instability often leads to cancer, mutations, and childbirth defects. Among them, DSBs are considered a very lethal result of ionizing radiation.

3 Ionizing and Nonionizing Radiations

Radiation can be either ionizing (long wavelength with low frequency and thus contains lower energy) or nonionizing (short wavelength with high frequency that has higher energy) (Ng 2003; Zamanian and Hardiman 2005). Nonetheless, ionizing radiation (IR) contains ample energy for producing ions at the molecular level. Radiations are of three types: (1) Alpha (α) radiation, consisting of alpha particles that are emitted from radioactive isotopes; (2) Beta (β) radiation, which transmits a high-energy electron with a negative charge that has greater penetrating power than alpha radiations; and (3) Gamma (γ) radiation, which is electromagnetic radiation like visible light, ultraviolet (UV) light, and radio waves (Zamanian and Hardiman 2005). Ionizing radiations contain electromagnetic energy (Dartnell 2011). IR is a type of electromagnetic radiation, which is generated when atoms absorb and release energy that could be coming from sunlight, fire, iron, visible light, x-rays, γ rays, and domestic utilization of heating artifacts (Cho et al. 2009; Zamanian and Hardiman 2005). IR tends to ionize the atoms of the living organisms, damaging living tissues and causing alterations in the genome of living organisms (Desouky et al. 2015). However, living organisms possess the ability to efficiently repair this damage and undo the genetic alterations caused by IR. Although IR can kill almost all forms of life, nevertheless it is not effective against all types of viruses (Gomes et al. 2017). The γ-ray is electromagnetic radiation with very high energy that can be transmitted into human and animal bodies and causes mutation (Shaban et al. 2017). However, γ-ray can also be useful to improve the morphophysiological characteristics and productivity of several crops such as sorghum, maize, and barley (Goron and Raizada 2015). Furthermore, in crop breeding, physical mutagens (UV light, X-rays neutrons, and alpha-beta particles), and thermal neutrons, especially γ-rays, are more useful than chemical mutagens (ethyl methanesulfonate) to develop mutant lines (Beyaz and Yildiz 2017). The γ-rays can influence seed germination by inducing free radicals in seeds (Zani et al. 2017).

Exposure to UV radiation often leads to cell death due to persistent DNA damage in the longer run. Recently, a gene product known as p53 has been discovered to be involved in regulating the cell cycle (Matsumura and Ananthaswamy 2004). In case of repairable damage to cells caused by UV radiations, p53 activates the repair machinery to restore cell’s functioning. However, in case of irreparable damages, the cells are subjected to apoptosis, which is the programmed death of damaged cells (Lieberman 2008). Molecular studies have further revealed that multiple genes are involved in the programmed death of damaged cells under long-term exposure to UV radiation (Nawkar et al. 2013). However, repeated and prolonged exposure to UV light leads to the synthesis of more thymine dimers in the DNA, which multiplies the risk of incorrect repairs of DNA bases, and the utter disruption or malfunctioning of cellular processes (Friedberg 2003). Subsequently, cells died in case of severe damage, while a small-scale incorrect repairing leads to cancerous cells’ formation.

4 Indoor Plants as Radiation Protectors

Small gardens at homes, offices, and study rooms can be used not only for ornamental purposes but also for other benefits such as flower therapy and health repair (Hall and Dickson 2011). Plants absorb harmful radiations emitted around our surroundings from electric and electronic gadgets like smartphones, laptops, laser machines, and microwave ovens. (Schmor 2011). Specific indoor anti-radiation plants constitute a significant source to detoxify air polluted with radiation. It also helps to increase the human metabolism and immune system by a positive impact on health and reduce the frequency of stress by minimizing headaches (Portelance et al. 2001). A non-exhaustive list of plants with a strong anti-radiation activity includes cactus, spider plant, aloe vera, sunflower, snake plant, and rubber plant (Arora et al. 2005; Astuti et al. 2020), as shown in Table 1.

Table 1 Brief description of the anti-radiation activity of some indoor plants
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5 Radioprotective Ability of Botanicals Against the Ionizing Radiations

The results obtained from various in vitro and in vivo studies indicate that various plants (such as Ocimum sanctum, Gingko biloba, Panax ginseng, Amaranthus paniculatus, Tinospora cordifoila, Hippophae rhamnoides, Centella asiatica, Podophyllum hexandrum, Emblica officinalis, Piper longum, Phyllanthus amarus, Mentha piperita, Mentha arvensis, Zingiber officinale, Syzygium cumini, Aegle marmelos, Carica papaya, Apium graveolens, Camellia sinensis, Curcuma longa, Caesalpiniadigyna, Aphanamixis polystachya, and Ageratum conyzoides) can protect against radiation-induced DNA damage, lipid peroxidation, and lethality (Jagetia 2007). Apart from these herbal plants, there are various ornamental herbs and shrubs such as Hedera, Piper, Ficuslyrata, Brassicasps. Heveabrasiliensis, Dracaena, Chlorophytum comosum, Ceratopteris thalictroides, Lithops pseudotruncatella, and a few grass species as Cypress and Asparagus, and legumes like soybean (Glycine max) that possess the ability to absorb harmful radiations and thus can play a crucial role to combat lethal irradiations. When a molecule absorbs energy through interaction with radiation, it is considered activated. In this energy-rich state, it may experience various abnormal chemical reactions, which are usually unavailable under thermal equilibrium, directly or indirectly, thus altering molecule structure. In some cases, radiation absorption is enough to get rid of an electron, thus leading to bond breakage at the molecular level (Fig. 2).

Fig. 2
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Anti-radiation activities of some indoor plants

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6 Importance of Radio-Protectors for Human Health

Radioprotectors entail cumulative measures to ensure human health against the harmful and damaging effects of radiations, especially ionizing radiations (Spitz and Albert 2001). These effectively protect humans from harmful radiations, including β, γ, UV, and radio waves. Ionizing radiations impart injuries that lead to malfunction of biological systems and therefore, it is pertinent to employ pharmacologically dynamic radioprotectors to offer adequate protection against harmful radiations. The upregulation of repair activity of damaged DNA can also constitute a neutralizing strategy against the damaging effects of radiations (Adhikari et al. 2007). Another neutralizing mechanism against the detrimental impact of ionizing radiations involves protein kinase (PK)-C inactivation and downregulation of factors responsible for the damages at the molecular level (Erickson III et al. 2015). Radioprotectors help humans and help plants by absorbing harmful radiation above its optimum range, as these radiations create stressful conditions in plants, leading to the accumulation of toxic compounds and the formation of ROS in plants. These harmful radiations increase the content of polyphenols in legumes by 8.5-folds (Sreekumar 2007) and drop the ATP content in cells of Solanum lycopersicon by 30%, affecting all ATP dependent pathways and leading to the formation of toxic compounds in plant cells. Exposure to harmful radiation like UV-A, UV-B, and EMF reduces plants’ oxidative response to high-salt concentration in Triticum aestivum (Dawood et al. 2021). Radioprotectant plants can absorb most of these radiations, helping other plants carry out their normal metabolism and indirectly benefitting humans and other species dependent on them from toxic compounds (Ali et al. 2015).

7 Possible Mechanisms of Radioprotection Adopted by Plants

Global warming and the increasing intensity of UV radiation due to ozone depletion are drastically affecting the growth of plants. The extent of these adverse effects usually varies depending on the wavelength and duration of exposure of plants to radiations (Ballare et al. 2011). Plants tend to respond to light through their photoreceptors and subsequently exhibit photomorphogenic development. In addition to photosynthetically active radiations (PAR; 400–700 nm), plants get subjected to UV radiations comprised of UV-A (320–390 nm), UV-B (280–320 nm), and UV-C (below 280 nm). The ozone layer protects the earth from UV-C radiation. The UVR8 protein acts as a receptor for UV-B radiation in plants. A lower UV-B exposure level initiates signaling through UVR8 and induces secondary metabolite genes involved in protection against the UV-B, while its higher dosages are detrimental to plants (Nawkar et al. 2013). Research reports that exposure to UV radiations generates ROS in mitochondria and chloroplast as a byproduct of essential energy-generating processes such as photosynthesis and respiration (Nawkar et al. 2013). Plant responses upon exposure to different UV radiations are activated through the involvement of different hormones. The salicylic acid levels increased in plants when exposed to UV-B radiations. Exposure to radiation does not alter jasmonic acid levels but increases plants tissue sensitivity towards the jasmonic acid. In plants, salicylic acid, jasmonic acid, and ethylene levels are changed in response to diverse external stresses such as ozone exposure and UV-B (Soheila 2000; Liu et al. 2012). The UV exposure represses a specific set of up-down genes regulated by the UV effects (Gomes et al. 2018). The underlying mechanism behind radioprotection offered by plants is the synthesis of vital chemical compounds such as polyphenols and numerous other antioxidants that perform scavenging activity for radiation-induced free radicals (Bhat et al. 2015). The synthesis of polyphenols in response to radiation exposure helps plants to upregulate antioxidants (catalase, superoxide dismutase, glutathione peroxidase, glutathione transferase, etc.) and mRNAs thereby reducing the oxidative stress caused by the ionizing radiations.

The putative mechanisms for radioprotection involve the production of antioxidants (-SH, GHS, GST, CAT, COD, mRNA GSH, GST) (Surapaneni and Jainu 2014). Remarkably, a variety of plants and herbs possess the ability to serve as radioprotectors, which may be exploited to cope with the adverse effects of radiations. There is a dire need to increase our understanding of plants’ ability to reduce damages caused by radiations through their scavenging activity of free radicals, synthesis of various antioxidants, inhibiting apoptosis, and modulation of growth factors, cytokines, and redox genes. The evaluation techniques based on fractionation can generate advanced information regarding plants’ ability to radio protect human beings. Advancement in nonprotein sulphydryl groups and reduction in lipid peroxidation indicates radioprotective activity. The plants and herb may also inhibit activation of mitogen-activated protein kinase (MAPK), protein kinase C (PKC), nitric oxide (NO), cytochrome P-450, and several other genes that are responsible for inducing damage after irradiation (Jagetia 2007). The anticancer and radioprotective properties of several plant-based natural products have been explored (Fig. 3). Due to the limitation of cost and side effects, there is an urgent need to explore safe, effective, and economic radiation protection agents, especially those of plant origin (Painuli and Kumar 2016).

Fig. 3
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Cellular mechanisms of radioprotection in plants (adapted from Painuli and Kumar 2016)

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8 Conclusion

The usefulness of UV radiations and other forms of primers in medical, engineering, agricultural, and other applied fields, and how humans rely on electronic technology in the modern era is well established. This chapter highlighted some detrimental impacts of radiation on human health. Various indoor plants and herbs have the potential to absorb and tolerate these harmful radiations through an array of biochemical and molecular mechanisms. Most of these plants and herbs have the potential as future radioprotectors which are also important for radiation control. The identification, characterization, and plantation of such plants in our surroundings are crucial to protect human health from radiation.