Growing seedlings in a Random Positioning Machine under a photoperiod regime promotes plant adaptation to microgravity environment by restoring meristematic competence
Abstract
The microgravity environment, as it exists in spaceflight, produces serious alterations in meristematic cells of plants. Meristems are fundamental tissues for plant growth and development since they are the reserve of undifferentiated totipotent cells, supplying differentiated cells to build the plant body throughout the entire life of the plant. Phototropism and gravitropism greatly influence meristematic activity, acting on the balance between the rates of cell growth and cell proliferation that defines meristematic competence. Thus, in the absence of gravity, understanding the role of a light stimulus is key for enabling plant adaptation to extraterrestrial environment. Here we have investigated the use of an illumination regime - photoperiod, applied to seedlings growing in a microgravity environment, as a countermeasure to reverse the effects caused by the lack of gravity orientation in darkness, on meristematic cells. Our experiments have used simulated microgravity, a useful complement to spaceflight in studies on the early plant development adaptation to extraterrestrial environments. The Random Positioning Machine was chosen as a reliable, well-characterized microgravity simulator. We have applied two illumination regimes, either photoperiod or darkness, and we have evaluated the status of meristematic competence in the root, in 6-day-old seedlings. We have paid special attention to the process of ribosome biogenesis, an essential cellular function, closely linked to cell growth, which is a major contributor to meristematic competence. For this purpose, we have used wild type Arabidopsis thaliana Col-0 ecotype and mutants of the two genes of the essential nucleolar protein nucleolin (NUC1 and NUC2). Some analyses have been performed separately in roots and hypocotyls (aerial parts) of seedlings grown in different conditions. Key parameters of cell proliferation (cell cycle regulation) and cell growth (ribosome biogenesis), as well as of auxin transport, were measured in the root meristem using in situ cellular markers and transcriptomic methods, compared with a 1g control. The results showed that the incorporation of an illumination regime, in this case photoperiod, has been sufficient to attenuate or suppress the effects caused by gravitational stress at the cellular level in the root meristem. In all cases, parameters recorded from samples receiving light stimuli in simulated microgravity were closer to 1g values than those obtained from samples grown in darkness. Differential results were obtained in the two nucleolin mutants. We conclude that light signals may totally or partially replace gravity signals significantly improving plant growth and development in microgravity. Despite that, molecular alterations are still compatible with the expected adaptation mechanisms that should be better understood. The differential sensitivity of nuc1 and nuc2 mutants to gravitational stress points to new strategies to produce more resilient plants to travel with humans in new extraterrestrial endeavors. Supported by Spanish AEI Grant #RTI2018-099309-B-I00 (co-funded by EU-ERDF) and by ESA-CORA-Ground Based Facilities Program, contract #4000105761.
- Publication:
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43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E1825M