Plant biology in space: recent accomplishments and recommendations for future research

Abstract

Gravity has shaped the evolution of life since its origin. However, experiments in the absence of this overriding force, necessary to precisely analyse its role, e.g. for growth, development, and orientation of plants and single cells, only became possible with the advent of spaceflight. Consequently, this research has been supported especially by space agencies around the world for decades, mainly for two reasons: first, to enable fundamental research on gravity perception and transduction during growth and development of plants; and second, to successfully grow plants under microgravity conditions with the goal of establishing a bioregenerative life support system providing oxygen and food for astronauts in long-term exploratory missions. For the second time, the International Space Life Sciences Working Group (ISLSWG), comprised of space agencies with substantial life sciences programmes in the world, organised a workshop on plant biology research in space. The present contribution summarises the outcome of this workshop. In the first part, an analysis is undertaken, if and how the recommendations of the first workshop held in Bad Honnef, Germany, in 1996 have been implemented. A chapter summarising major scientific breakthroughs obtained in the last 15 years from plant research in space concludes this first part. In the second part, recommendations for future research in plant biology in space are put together that have been elaborated in the various discussion sessions during the workshop, as well as provided in written statements from the session chairs. The present paper clearly shows that plant biology in space has contributed significantly to progress in plant gravity perception, transduction and responses - processes also relevant for general plant biology, including agricultural aspects. In addition, the interplay between light and gravity effects has increasingly received attention. It also became evident that plants will play a major role as components of bioregenerative life support and energy systems that are necessary to complement physico-chemical systems in upcoming long-term exploratory missions. In order to achieve major progress in the future, however, standardised experimental conditions and more advanced analytical tools, such as state-of-the-art onboard analysis, are required.

Mechanical Stimulation Modifies Canopy Architecture and Improves Volume Utilization Efficiency in Bell Pepper: Implications for Bioregenerative Life-support and Vertical Farming

“…Humans require significant countermeasure interventions to reduce the negative impacts of microgravity on bone and muscle tissue (Baldwin et al 1996); it stands to reason that crop plants making up part of a bioregenerative life-support system may also benefit from microgravity countermeasures. In the absence of a significant gravity vector plant cell walls and, by elaboration, supporting tissues (e.g., branches supporting fruit) can be modified, although consensus on the degree and direction of the modifications is elusive (de Micco et al 2008, Ferl et al 2002, Hoson 2014, Levine et al 2001, Matía et al 2010, Ruyters & Braun 2013. Very little (if any) research has examined the effects of direct mechanical stimuli on crop plants in a microgravity setting.…”

Patterning of plant cell wall deposition by cortical microtubules

“…This indicates that gravity does not sufficiently affect microtubule patterning to change patterned deposition of SCTWs during protoxylem formation. This is a favourable result considering that viable plants with normal plant growth are necessary in bioregenerative life support system to facilitate long-term space missions in the future 107 . It is not likely that microgravity in space will affect protoxylem formation and thereby reduce plant development resulting in unviable plants.…”

European parabolic flight campaigns with Airbus ZERO-G: Looking back at the A300 and looking forward to the A310

“…One group of scientists of the University of Bayreuth is investigating the effect of weightlessness on planktonic organisms like water fleas (Daphnia) during parabolic flights. More details about research in gravitational biology in space can be found in Ruyters and Braun (2014).…”