A new era of lunar exploration has started under the umbrella of the Artemis Program at NASA (Chavers et al., 2019). In the first phase (by 2024), NASA plans to return to the Moon and accomplishes the following tasks: (1) to send robotic landers and payloads to the lunar surface; (2) to assemble the Gateway outpost in lunar orbit; and (3) to resume the first human landings on the surface of the Moon since 1972. NASA’s Artemis Program will use a coordinated approach utilizing the resources of the entire agency including NASA centers with a possible focus on landing near the South Pole of the Moon. In the second phase (by 2028), NASA plans to establish a sustained human presence on the Moon. The agency believes that the technologies and instruments developed during Artemis will be useful for future human missions to Mars.
In addition to human spaceflight that is part of Artemis, NASA has developed the Commercial Lunar Payload Services (CLPS) program to send relatively small (<500 kg) robotic landers to the Moon (Chavers et al., 2019). The goals of CLPS include determining whether there are lunar resources for future human missions and conducting science experiments related to Artemis. The first landers under CLPS to land on the Moon are scheduled to be built by Astrobotic (Pittsburgh, PA, USA) and Intuitive Machines (Houston, TX, USA). Based on our previous research on the International Space Station (ISS), we predicted that lunar gravity may be insufficient for normal plant growth and development while Martian gravity is adequate (Kiss et al., 2012; Vandenbrink et al., 2016). These results have profound implications for human exploration plans and the use of a Moon base as a stepping stone to Mars.
We have proposed a plant biology experiment on one of the early CLPS lunar landers that would be in a greenhouse housed in a CubeSat system. Thus,
The first CLPS lunar landers have severe restrictions on power and mass, and mission resources available for biological experiments are very limited. In designing experiments with CubeSat on the Moon, a broad spectrum of temperature tolerance needs to be considered for growing
This widest temperature range is in contrast to our previous experiments conducted with
Fortunately, since
Several studies have focused on the physiology and development of natural ecotypes of
Thus, for the reasons for our proposed study, we tested for temperature effects on germination and seedling growth from
Thus, our working hypothesis regarding ecotypes of
We studied several natural ecotypes of the plant
Key characteristics of the seed stocks of the nine ecotypes used in these studies.
Tenela | Te-0 | N63° | 1–100 | 0–2/7–8 | Finland | ABRC | CS1550 |
Sweden | SW | N62° | NA | NA | Sweden | MSU | ** |
Osthammar | Ost-1 | N61° | 1–100 | 0–2/5–6 | Sweden | ABRC | CS1430 |
Columbia | Col-0 | N52° | 1–100 | 15–16/21–22 | Poland | MSU | ** |
Dresden | Dr-0 | N51° | 100–200 | 7–8/9–10 | Germany | ABRC | CS1114 |
Italy | IT | N42° | NA | NA | Italy | MSU | ** |
Coimbra | Co-2 | N40° | 100–200 | 11–12/17–18 | Portugal | ABRC | CS1086 |
Martuba | Mt-0 | N28° | 100–200 | 15–16/15–16 | Libya | ABRC | CS22642 |
Cape Verde Is | Cvi-0 | N16° | 1200 | NA | Cape Verde | ABRC | CS8580 |
ABRC, Arabidopsis Biological Resource Center (
Seeds of
Following surface sterilization, seeds were placed in two rows into each Petri dish. The agar dishes with seeds were then wrapped in Parafilm and left for 72 h at 4°C to stimulate germination. After seed stratification, the plates were placed vertically and continuously illuminated for 10 days with white light fluorescent tubes (120–140 mmol m−2s−1) in one growth chamber at 25, 30, or 35°C and in another growth chamber (approximately 240–260 mmol m−2s−1) at 11 °C or 15 °C, respectively. For germination tests, the number of seeds used for each ecotype and temperature is shown in Table 2. [However, we believe that it may be difficult to add a stratification step to the lunar experiment given our understanding of mission constraints.]
Number of seedlings grown from each ecotype and used for the temperature experiments.
nt | 36 | 24 | nt | 37 | |
48 | 36 | 36 | 48 | 36 | |
nt | 24 | 24 | nt | 20 | |
48 | 36 | 36 | 48 | 36 | |
nt | 36 | 24 | nt | 36 | |
48 | 36 | 33 | 48 | 37 | |
nt | 27 | 24 | nt | 24 | |
23 | 36 | 36 | 25 | 36 | |
nt | 33 | 24 | nt | 36 |
“nt” = not tested because of limited seed stock.
Seedlings in Petri dishes were imaged periodically with a Canon EOS Rebel T6 DSLR camera and with a Epson V600 Photo Scanner at termination on the 10th day. Growth and morphometricproperties were measured using the Fiji-win64 software. For each ecotype, the following growth parameters were measured: number of leaves, area of leaves, main root length, number of secondary roots, and the total root length. All analyses were performed with the RGui 64-bit R 3.5.1 for Windows with R Commander package (R Development Core Team, 2008).
Seed germination was assayed in the nine ecotypes of
Figure 1
Studies of seed germination of various ecotypes of

We also examined the morphological features of the plants at different temperature treatments. In terms of leaf development, as with the data on germination, the best results across all ecotypes were at 15 and 25 °C (Figure 2). Thus, the greatest number of leaves (Figure 2A) and the largest leaf area (Figure 2B) occurred when seedlings were incubated at 15 and 25 °C. Similar to the seed germination studies, the best results were obtained with the Col-0 and the Mt-0 ecotypes. At the 30 °C incubation point, only the Col-0, SW, and Mt-0 (but not the IT ecotype) showed limited growth of leaves, while there was no growth for any of the ecotypes tested at 35 °C.
Figure 2
Leaf development assayed by the (A) number of leaves and (B) total area of the leaves in the seedlings at the indicated temperatures in continuous illumination. In terms of the number of leaves (A), the Col-0 ecotype had the greatest number of leaves for all temperatures tested. As indicated by leaf area (B), Col-0 had the largest area when the data were taken together from 11 to 25 °C while the Mt ecotype was an overall second in this latter criterion. The sample sizes are provided in Table 2. Bars indicate SE.

The results of the studies of root development (Figure 3) were generally similar to those obtained with investigations of the leaves. In terms of the main root (Figure 3A), the greatest length across all ecotypes was at 15 and 25 °C. The best performers on this parameter again were the Col-0 and the Mt-0 ecotypes. Across all ecotypes, the largest number of secondary roots (Figure 3B) occurred when the seedlings were incubated at 15 and 25 °C, with the Col-0 and the Mt-0 ecotypes exhibiting the greatest number of secondary roots. In terms of the final measurement considered, the length of the total root network (including both the primary and secondary roots; Figure 3C), the results are similar to the previous two parameters. For all three root criteria, there was little or no growth in any of the ecotypes at 30 and 35 °C (Figure 3).
Figure 3
Root development as determined by the (A) main root length, (B) number of secondary roots, and (C) length of the total root network of the seedlings at the indicated temperatures in continuous illumination. Based on these criteria, Col-0 exhibited the most robust growth from 11 to 25 °C. The sample sizes are provided in Table 2. Bars indicate SE.

Images of seedlings of the Col-0 (Figure 4) and the Mt-0 (Figure 5) ecotypes illustrate the differences in the development of the shoot and root systems at the different temperatures studied. Seedlings of the Col-0 show robust growth with a well-developed shoot system and an extensive primary and secondary root networks when incubated at 15 and 25 °C, but there was also good growth at 11 °C (Figure 4). Mt-0 seedlings grow well at 15 °C but have more robust growth at 25 °C (Figure 5). Taken together, when considering seed germination and seedling development, the Col-0 ecotype performed better than the other ecotypes studied at all temperatures tested in these experiments.
Figure 4
Images of seedlings of the

Figure 5
Images of seedlings of the

Hundreds of ecotypes of
However, our initial prediction was not supported by the results obtained in the present study. The Columbia ecotype (Col-0), which can be traced to origins in Poland at 53°N latitude (Fernandez et al., 2018), performed best at a wide range of temperatures from 11 to 30 °C. However, while there was seed germination at 30 °C and even at 35 °C, acceptable growth occurred in the range of 11–25 °C. The next best ecotype in terms of these germination and growth parameters was Mt-0, which is from a Libyan population 28°N latitude (Alonso-Blanco et al., 2016). However, based on the studies to date, Col-0 alone is our preferred choice in these proposed experiments as it performed much better than all of the other genotypes tested in these studies.
Spaceflight opportunities are relatively rare and expensive (Vandenbrink and Kiss, 2016), so it is important to do extensive ground-based testing of many parameters to optimize the flight experiments (Kiss, 2015). In our previous spaceflight experiments, we performed extensive testing to ensure success (Katembe et al., 1998). For example, in the initial EMCS project, we performed extensive ground-based studies as the hardware and the facility were both new. Thus, we tested the effects of storage of seeds on germination and growth as well as cold storage procedures following the termination of the experiment (Kiss et al., 2009). In some of our later EMCS experiments, we improved the lighting and imaging by using infrared illumination to provide high-quality images of the seedlings (Vandenbrink et al., 2019), and ground-based studies were important in identifying and optimizing these parameters (Kiss et al., 2014). Thus, in the present study, we continued using this general approach to determine the optimal temperature range for growing plants in a lunar greenhouse experiment.
In contrast to our initial working hypothesis of using several ecotypes of
This wider temperature range will give engineers greater flexibility in designing a thermal system in the CubeSat that will be tethered to and acquire power from the robotic lunar lander (Kitto et al., 2020). Our future research will help to establish additional parameters of growing plants in the lunar environment, which will be important in the long-term for using plants as part of a bioregenerative life support system needed for human exploration of the Moon and perhaps Mars (Kiss, 2014).
Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Key characteristics of the seed stocks of the nine ecotypes used in these studies.
Tenela | Te-0 | N63° | 1–100 | 0–2/7–8 | Finland | ABRC | CS1550 |
Sweden | SW | N62° | NA | NA | Sweden | MSU | ** |
Osthammar | Ost-1 | N61° | 1–100 | 0–2/5–6 | Sweden | ABRC | CS1430 |
Columbia | Col-0 | N52° | 1–100 | 15–16/21–22 | Poland | MSU | ** |
Dresden | Dr-0 | N51° | 100–200 | 7–8/9–10 | Germany | ABRC | CS1114 |
Italy | IT | N42° | NA | NA | Italy | MSU | ** |
Coimbra | Co-2 | N40° | 100–200 | 11–12/17–18 | Portugal | ABRC | CS1086 |
Martuba | Mt-0 | N28° | 100–200 | 15–16/15–16 | Libya | ABRC | CS22642 |
Cape Verde Is | Cvi-0 | N16° | 1200 | NA | Cape Verde | ABRC | CS8580 |
Number of seedlings grown from each ecotype and used for the temperature experiments.
nt | 36 | 24 | nt | 37 | |
48 | 36 | 36 | 48 | 36 | |
nt | 24 | 24 | nt | 20 | |
48 | 36 | 36 | 48 | 36 | |
nt | 36 | 24 | nt | 36 | |
48 | 36 | 33 | 48 | 37 | |
nt | 27 | 24 | nt | 24 | |
23 | 36 | 36 | 25 | 36 | |
nt | 33 | 24 | nt | 36 |
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