1Department of Biosciences, M. D. University, Rohtak-124001, India.
2Department of Pharmacology, University of Connecticut Health Centre, Farmington, USA.
* Corresponding author. E-mail: shyamnmishra@yahoo.com
Heavy ion radiations; linear energy transfer; relative biological effectiveness; Restriction-fragment length polymorphism, Total energy per nucleon (n) or mass (u), Energy transfer at the target per micron or micrometer surface area.
Heavy ion radiations (HIR), feature of the outer space environment limiting life during space mission was evaluated for responses in algae, fungi and dormant seeds. The results obtained mostly are elusive due to unequivocal irradiation doses and microgravity/weightlessness in space. Hence, HIR simulated experiments on earth are performed to understand precisely growth and developmental changes in plants by the operation of heavy ion accelerators at various institutes around the world. Seeds exposed to various heavy ions have shown inhibition in germination and morphological abnormalities in seedlings. Plants tumorous growth, chromosomal aberration and certain mutations due to DNA break and/or miss-repair or transposition is also observed. These might hamper cellular activity leading to lethality. Additionally, the experiments suggest that prolonged exposure of seed/seedling to HIR during space flight or during simulated experiments may cause differential biological effects. Plant differential responses could be attributed to heavy ion irradiation dose, plant species and its physiological state. It is tempted to suggest that heavy ions/charged particles with specific dose might activate or modify certain processes which might result into few useful plant characters. The heavy ion potential to generate mutants because of localized deposition and/or hitting the molecule in exposed plant tissues make sense to consider it as an alternative tool either for conventional breeding or for genetic modulation in a way to improve the growth and yield of crop plants or to develop stress tolerant strains for farming, in changed agro-climatic conditions. The bystander effect (induced response in cells other than targeted one) in plants is yet to be examined as in animal system. Our understanding of fundamental mechanisms of changing plant system exposed to HIR is still incomplete. More detailed studies on plant physio-chemical regulation, radiation induced mutation, kinetics of DNA repair under heavy ion exposure and microgravity may help in drawing strategies for terrafarming. The variation in radio-sensitivity of plants further gives strong note to perform extensive experiments at molecular level for requisite focus of character and screening of plants for space mission.
Heavy ion irradiation, mutations, plant growth, space-flight responses
