Arabidopsis grew in Apollo lunar regolith but showed signs of stress

Lunar regolith is the loose material covering the Moon’s surface. Unlike terrestrial soil, it is mineral material without organic matter; its particles and fragments come from the lunar surface. To study how a terrestrial plant responds when growing directly in it, a team sowed Arabidopsis thaliana in samples returned by the Apollo 11, Apollo 12 and Apollo 17 missions. The study was published in Communications Biology; the scientific article presents the experiment and its results.

The seeds germinated and the plants grew in all three samples, although development was slower than in the control grown in JSC-1A, a lunar-soil simulant. Plants grown in real regolith also had more stunted roots and less extensive leaf canopies. The experiment examined both these traits and the plants’ gene expression. This is a question of interest for studying cultivation systems that could be part of life support during future lunar stays: plants can produce food and oxygen, recycle water, and remove carbon dioxide from a habitat.

Three samples from Apollo missions

The samples bore the numbers 10084, 12070 and 70051 and came from Apollo 11, Apollo 12 and Apollo 17, respectively. All three were collected in lunar regions dominated by basaltic mineralogy, but they represent regoliths with different degrees of maturity. In this context, maturity describes the material’s exposure at the lunar surface and to the processes acting on it.

The team classified the Apollo 11 sample as mature and the Apollo 12 sample as submature. The Apollo 17 sample was an immature mixture, with a shorter exposure time and material from several areas of the landing site. To compare growth, the researchers used JSC-1A, a lunar-regolith simulant, as the control material. Thus, the study compared plants grown in authentic lunar samples with plants grown in a material prepared to simulate lunar soil.

The species selected was Arabidopsis thaliana, a small plant used in research. Eos’s report on the experiment explained that the team analyzed gene expression after 20 days of growth. The observations described relate to this species, the three specific samples and the conditions of the experiment.

Germination and stress responses

Compared with control plants in JSC-1A, those grown in real lunar regolith grew more slowly and had more stunted roots and less extensive leaf canopies. They also showed visible signs of stress, including more intense green or purple pigmentation. The study described severe stress morphologies in many of the plants.

Genetic analysis detected changes in the expression of genes associated with ionic stress in plants grown in the lunar samples. According to the researchers, the responses observed were similar to those plants exhibit under stress related to salts, metals and reactive oxygen species. Thus, germination and growth took place alongside observable signs of stress, both in the plants’ appearance and in their gene-expression patterns.

The team proposed that chemical differences between authentic regolith and the simulant could help explain some of the difficulties. In its coverage of the study, Eos pointed to the chemical form of iron as an example: lunar material contains iron associated with interactions with the solar wind, while simulants and terrestrial soils may contain different forms that are more accessible to plants. Stephen Elardo, a planetary geochemist at the University of Florida and a co-author of the study, told Eos that simulants can be useful for engineering questions, but do not necessarily reproduce identically the chemistry available to plants.

Stress varied among the regoliths

Plants grown in the Apollo 11 sample were the most stressed, while those grown in the Apollo 17 sample were the least stressed. The comparison is consistent with the maturity classification: Apollo 11 represents the most mature material of the three sites, and Apollo 17 an immature mixture with less time exposed at the lunar surface.

According to Eos’s report, longer exposure allows processes such as the solar wind, cosmic rays and micrometeorite impacts to act. These processes can alter the regolith’s chemistry, granularity and glass content. Co-author Anna-Lisa Paul of the University of Florida told the outlet that the material’s provenance may matter when selecting it as a growing substrate. The result observed in the samples highlights that materials from different locations and with different degrees of maturity were associated with different plant responses.

What the experiment contributes to lunar exploration

The experiment showed that Arabidopsis thaliana germinated and grew in all three regolith samples examined, and documented differences in development and signs of stress. This provides information for investigating the possible use of local resources in lunar cultivation systems. The authors consider that the interaction between plants and regolith should be studied in greater detail and probably mitigated to facilitate efficient use of this material in life-support systems for lunar stations.

The scope of the results is limited to the plant and materials tested: Arabidopsis thaliana and samples returned by Apollo 11, Apollo 12 and Apollo 17. The experiment provides observations under those experimental conditions, including the difference between lunar regolith and the simulant used as a control. The authors propose as a next step to clarify the interaction between plants and lunar material.

Overall, the samples allowed germination and growth, but development was slower than in the simulant and was accompanied by stress responses. The observed intensity also varied among samples. These results provide a basis for further study of how lunar material and its provenance relate to plant growth in research on future habitats.