Comparison of Microgravity Analogs to Spaceflight in Studies of Plant Growth and Development

Abstract

Life on Earth has evolved under the influence of gravity. This force has played an important role in shaping development and morphology from the molecular level to the whole organism. Although aquatic life experiences reduced gravity effects, land plants have evolved under a 1-g environment. Understanding gravitational effects requires changing the magnitude of this force. One method of eliminating gravity'’s influence is to enter into a free-fall orbit around the planet, thereby achieving a balance between centripetal force of gravity and the centrifugal force of the moving object. This balance is often mistakenly referred to as microgravity, but is best described as weightlessness. In addition to actually compensating gravity, instruments such as clinostats, random-positioning machines (RPM), and magnetic levitation devices have been used to eliminate effects of constant gravity on plant growth and development. However, these platforms do not reduce gravity but constantly change its direction. Despite these fundamental differences, there are few studies that have investigated the comparability between these platforms and weightlessness. Here, we provide a review of the strengths and weaknesses of these analogs for the study of plant growth and development compared to spaceflight experiments. We also consider reduced or partial gravity effects via spaceflight and analog methods. While these analogs are useful, the fidelity of the results relative to spaceflight depends on biological parameters and environmental conditions that cannot be simulated in ground-based studies.

The Emerging Role of Macrophages in Immune System Dysfunction under Real and Simulated Microgravity Conditions

“…Therefore, when ground-based microgravity experiments are carried out, the following items need to be carefully considered: (1) The biological state of the sample (such as gender, strain, and age) should be carefully considered in the experimental design stage; (2) ground-based experiments should be carried out to maximize the consistency of the experimental results between simulated microgravity and real microgravity so that the final consistent conclusion can be obtained; (3) given the sensitivity of biological samples to the external environment, the container of the device that simulates microgravity should be the same size as the container in the real space flight experiment system, although this experimental requirement may increase the cost of the real space flight experiment [ 110 , 111 ].…”

Immunity in Space: Prokaryote Adaptations and Immune Response in Microgravity

“…Clinostats rotate samples around one or more axes and were developed in the late 1800s when gravity was discovered to be a major factor in plant growth [ 17 ]. This goes back to as early as 1806 and the use of a water wheel to generate altered gravity environments [ 17 ].…”

“…Clinostats rotate samples around one or more axes and were developed in the late 1800s when gravity was discovered to be a major factor in plant growth [ 17 ]. This goes back to as early as 1806 and the use of a water wheel to generate altered gravity environments [ 17 ]. Slow rotation around an axis (1–2 rpm) was found in the 1980s to induce ultrastructural disturbances not found in the microgravity environment [ 18 ].…”

Root Tropisms: New Insights Leading the Growth Direction of the Hidden Half

“…Indeed, specific devices such as clinostats, random positioning machines (RPMs), and centrifuges, but also parabolic flights, drop towers, rockets, and magnetic levitation provide opportunities to explore plant tropisms in altered gravity. More specifically, clinostats and RPMs regularly change the direction of gravity perceived by the plant, whereas microgravity in space can be best described as weightlessness achieved by the balance between the gravity force and the centrifugal force of the object, which is also the case of parabolic flights and drop towers [ 11 ]. In this framework, although studies on Earth using devices which change the direction of gravity proved to be informative for certain parameters, findings necessitate space-based research to be validated [ 11 ].…”

“…More specifically, clinostats and RPMs regularly change the direction of gravity perceived by the plant, whereas microgravity in space can be best described as weightlessness achieved by the balance between the gravity force and the centrifugal force of the object, which is also the case of parabolic flights and drop towers [ 11 ]. In this framework, although studies on Earth using devices which change the direction of gravity proved to be informative for certain parameters, findings necessitate space-based research to be validated [ 11 ]. Currently, the possibility to perform experiments in space using laboratories onboard the ISS is gaining much interest in tropism research, especially for root tropisms, which are dominated by gravitropism [ 12 ].…”