Plants have evolved sophisticated morphological structures and bio-chemical mechanisms to counteract the stressors in their environment, which plants cannot avoid by simply moving elsewhere. However, the stressors of spaceflight such as altered gravity, increased radiation, and hypomagnetic fields, are rarely seen in any combination on Earth, and so plant responses to spaceflight are unique, complex, and understudied. Understanding and mitigating these stresses is critical to ensuring the self-sustaining food supply and bioregenerative life support required for long-duration space missions.
Ionizing Radiation
On Earth’s surface, ionizing radiation (IR) is relatively low ranging from 0.1-0.2 μSv h-1 [1] due to our protective magnetic field. In contrast, IR levels reaches 30 μSv h-1 on Mars, 57 μSv h-1 on the Moon, and 80 μSv h-1 outside any planetary protection [2], [3]. As plants have no known IR sensing pathways, their response to damage from IR is mainly derived from the consequences of exposure. One is the generation of reactive oxygen species (ROS), such as superoxide, hydrogen peroxide (H2O2), the hydroxide radical (OH–), and singlet oxygen (1O2) through radiolysis [4]. While ROS are a natural part of aerobic metabolism, excess generation as a result of IR, causes oxidative damage to DNA or biomolecules, including proteins, lipids, and cell walls [5]. IR also has the potential to directly damage DNA, resulting in mutations that can alter morphology, development, and seed viability [6], [7]. However, there may be beneficial responses, such as increased stress tolerances and phytochemicals [8]; but type of radiation, exposure time, and dosage each hold an influence in the positive or negative outcomes of IR exposure [1], [9], [10].
Magnetic Fields
Earth’s magnetic field (MF) ranges from 35-65 μT, on Mars it’s about 2 μT, on the Moon and in deep space it is less than 0.1 μT [11]. Plant responses to MF variation are not yet fully understood but numerous mechanisms surrounding cryptochrome and radical pairs have been proposed [5]. The ability of Drosophila (fruit flies) to sense MFs is well documented through a magnetosensor, MagR, which is built from an iron-sulfur cluster assembly (ISCA) and cryptochrome [12]. Plant magnetosensors are not well known but investigation reveals that they possess similar molecules to MagR such as: IscA-like 3, IscA-like 1, IscA-like 2, and cpIscA, which likely facilitate MF perception through singlet-triplet radical pair conversions [13], [14]. Hypomagnetic fields produce a variety of effects impacting the plants redox status, photosynthetic activity, and hormone balance that differ between crops [15]. Notably, ROS levels tend to be decreased under hypomagnetic conditions through the downregulation of ROS production and scavenging genes [16], [17]. Coupling the fact that IR results in an unprogrammed generation of ROS and low MF decreases the plants’ ability to combat this, it is critical to study the mechanisms and effects of the individual and combined effects of these spaceflight stressors.
Gravity
Plants have evolved to sense the gravity vector, guiding morphogenesis for the maximization of solar energy capture by leaves and water uptake by roots. Gravitational responses occur through three distinct phases; perception of gravity via statoliths granules settling in the direction of the gravitational pull [18]; transformation of perceived gravitational changes into a stimulus [19]; and, lastly, cellular responses to the stimulus [20]. However, linking the perception of gravity to molecular responses is an active area of study as the roles of Ca2+ and membrane lipids are implied but not yet fully understood [18], [19], [21], [22].
Within Earth’s 1 g (9.81 m s-1), plants properly orient themselves. Meanwhile under the Moon’s 0.17 g, Mars’ 0.38 g and micro- or zero-gravity, the plants’ ability to do so is impacted [21]. Exposure to short-term (seconds to hours) microgravity results in the upregulation of hundreds of genes corresponding to abiotic stress responses such as the production of ROS scavengers and heat shock proteins. With long-term exposure (days to months) plants acclimate, leaving only a few genes highly upregulated [19], [23]. However, combined with a disrupted ability to distribute the plant growth hormone auxin [24] plant growth is generally impaired in space.
Conclusion
This review barely scratches the surface of what exactly happens to plants when they leave Earth. There is an awful lot of literature that digs deeper, and even more answers that have yet to be discovered. Writing this reminded me of just how much remains to be understood about plants, which is critical, as they will need to travel the stars with us if we are to make it any significant distance away from Earth and stay there for a bit. In fact, that is one of the main draws for me to focus on spaceflight and controlled environments in general. These avenues really push the boundaries of what needs to be investigated providing motivation that would rarely arise from pure agricultural research.
Proudly written without large language models.
©Donald Coon 2025 available at https://doi.org/10.5281/zenodo.14953611
This work is licensed under CC BY 4.0
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Donald S. Coon 