A Chinese study team devised an experimental method through which they managed to reveal the effect of microgravity on radio-adaptive response in plants, reported in a paper published last week in Mutation Research / Fundamental and molecular mechanisms of mutagenesis. 

Radio-adaptive response (RAR) is a critical radiation effect due to both low-dose background and sudden high-dose radiation exposure during solar storms.

Although it is relevant to explore RAR under the condition of microgravity, which a major space environmental factor, there lacks existing studies to reveal its effects on RAR.

"In the study, we firstly established an experimental method to detect the effect of gamma-irradiation on the primary root growth of Arabidopsis thaliana, in which, we see that RAR of root growth was significantly induced by several dose combinations." said BIAN Po, the team leader, at Institute of Technical Biology & Agriculture Engineering, Hefei Institutes of Physical Science (CAHIPS) of the Chinese Academy of Sciences.

Microgravity was simulated using a two-dimensional rotation clinostat. It was shown that RAR of root growth was significantly inhibited under the modeled microgravity condition, and was absent in pgm-1 plants that had impaired gravity sensing in root tips. These results suggest that RAR could be modulated in microgravity.

After treatment with the modeled microgravity, attenuation in priming irradiation-induced expressions of DNA repair genes (AtKu70 and AtRAD54) and reduced DNA repair efficiency in response to challenging irradiation were observed.

In plant roots, the polar transportation of the phytohormone auxin is regulated by gravity; treatment with an exogenous auxin (indole-3-acetic acid) prevented the induction of RAR of root growth, suggesting that auxin plays a regulatory role in the interaction between microgravity and RAR of root growth.

Those work were supported by the grants from National Natural Science Foundation of China.

Fig 1. Effect of microgravity on the RAR of root growth. (A) Schematic representation of gamma-irradiation and microgravity simulation of Arabidopsis thaliana; (B) Root growth of seedlings subjected to 10 Gy of priming gamma-irradiation and 25, 50, 75, 100, 125, and 150 Gy of challenging gamma-irradiations; (C) Effect of modeled microgravity on the RAR induced by 10+50 Gy,10+75 Gy and 10+100 Gy dose combinations. (Image by DENG Chenguang)