M‐PHIS: A New Imaging System to Grow Plants on Mars

Abstract

Growing plants is an essential step to the colonization of other planets. These plants will have to adapt to a very different environment from the one on Earth. This article presents a new imaging system for evaluating plant health by measuring their fluorescence. The system was placed in a hypobaric chamber simulating the conditions under which it could have to operate during early missions and later the colonization of Mars. On Mars, the atmospheric pressure is below 1 kPa and thus for primarily reasons of structural mass savings, plant production facilities will likely be operated at a reduced (<1 atm) pressure. A second article entitled Experiments with the M‐PHIS to Grow Plants on Mars present the experiments performed on this system.

This article is part of a series on research and technological developments intended for the colonization of other planets.

Introduction

Humans face a variety of challenges as they continue to explore beyond the frontiers of planet Earth. Exploration missions are often severely constrained by launch mass and resupply considerations. The use of plants as part of life support systems continues to be explored as an approach for more sustained human presence in space. In particular, bioregenerative life support systems have been considered since the early 20th century (Wheeler, 2010). The Canadian Space Agency, University of Florida and University of Guelph have been involved in assessing the possibility of supporting human presence on the Moon and Mars by deploying greenhouses as plant production system test-beds (Bamsey et al., 2009a; Bamsey et al., 2009b). The main concept is the use of plants to regenerate the three cornerstones of human consumable requirements; air, water and food (Tamponnet et Savage, 1994).

Spaceflight and other extraterrestrial environments provide unique challenges for plant life. There originates the importance of understanding the metabolic issues that can influence plant growth and development in space. Plant monitoring systems with the capacity to observe the condition of the crop in real-time within these systems would permit operators to take immediate action to ensure optimum system yield and reliability. In addition to the utilization of chlorophyll fluorescence, specific stress response genes can be tagged with reporter genes encoding a variety of fluorescent proteins, allowing gene activities, and by extension plant health, to be monitored through the fluorescence of these gene products (Plautz et al., 1996).

The Transgenic Arabidopsis Gene Expression System (TAGES) is a biosensor that uses Arabidopsis thaliana fluorescence information from both naturally occurring chlorophyll red/near infrared fluorescence, as well as green fluorescence originating from the gene products of green fluorescent protein (GFP) reporter genes (Manak et al., 2002; Paul et al., 2003). Several commercial systems are available for imaging and capturing plant fluorescence, but most analytical procedures involve laboratory examination and human input. However, advanced biological experiments on orbit, the Moon, and Mars are likely to be autonomous, precluding any direct human control over the monitoring/imaging systems. Furthermore, if a mission does include a physical human presence, there are still system trade-off considerations between internal greenhouse/growth chamber operating pressure, up-mass and crew time requirements that may still dictate completely robotic and/or autonomous bioregenerative life support systems (Paul and Ferl, 2006).

Figure 1 Engineered Arabidopsis plants. Green color shows where green fluorescent protein (GFP) is being expressed, and red shows the natural fluorescence of chlorophyll.

A Multispectral Plant Health Imaging System (M‐PHIS) would provide a considerable step forward in our capacity to monitor advanced life support crops in an autonomous manner (Baker et Rosenqvist, 2004; Ehlert et Hincha, 2008; Galston, 1992; Lichtenthaler et Babani, 2000; Manak et al., 2002). This article describes the design and development of a prototype multispectral fluorescent imaging system deployed in a hypobaric plant growth chamber at the University of Guelph. The imager was designed primarily for multiband imaging of chlorophyll and protein fluorescence with the design being driven by portability and autonomous functionality considerations. The design was also novel in that it employed a commercially available liquid crystal tunable filter (LCTF) and a custom developed LED board with an independently variable grow light LED array.

Figure 2 Multispectral Plant Health Imaging System (M‐PHIS) Front (A), Back (B)

Hypobaric Plant Growth Chambers

A hypobaric environment has a pressure lower than the atmospheric pressure. The atmospheric pressure on Earth is 101.3 kPa at sea level and decreases with altitude to reach about 30 kPa at the top of the Himalayas. The average pressure on Mars is 0.6 kPa or about 170 times less than on Earth. Plants can grow at very low absolute pressure provided the partial pressure of oxygen is increased compared to normal.

In order to simulate spaceflight deployment conditions that the imager may be expected to perform under, a hypobaric chamber was used to isolate the imager and to serve as a platform for long duration operational tests. This represents one of a number of possible space analogues and on orbit deployment scenarios. A canopy scale hypobaric plant growth chamber (Figure 3) at the University of Guelph‘s (Ontario, Canada) Controlled Environment Systems Research Facility (CESRF) was utilized for the test. The CESRF maintains and operates 20 sealed environment chambers including 14 variable pressure chambers capable of sustaining a near vacuum (<1 kPa) (Bamsey et al., 2009b). Of these 20 chambers, five are fully automated canopy-scale hypobaric chambers and measure 1.0 x 1.8 x 2.5 m with a total volume of approximately 4500 liters and providing a plant growth area of 1.5 m² (Wehkamp et al., 2012). The light canopy, irrigation and nutrient control system is outlined in the following Figure.

Figure 3 Canopy-scale hypobaric chambers at the Controlled Environment Systems Research Facility (CESRF), University of Guelph: A) Exterior showing lighting canopy, irrigation and nutrient control system, B) M-PHIS deployed in a CESRF hypobaric plant growth chamber.

Multispectral Plant Health Imaging System (M‐PHIS)

The Multispectral Plant Health Imaging System (M‐PHIS) (Figure 3) is a modified version of the TAGES Imaging System-III (TIS-III), which was deployed in the Arthur Clarke Mars Greenhouse in the High Arctic on Devon Island (Abboud et al., 2013a). The M‐PHIS boasts several new features including the capacity to capture images at a variety of wavelengths. In addition to capturing GFP expression, M-PHIS could be employed to capture yellow and red fluorescent proteins as well as chlorophyll’s red/near infrared florescence and more. The second most important feature is the independently controllable plant grow light wavelengths. The user has the capacity to set the grow light intensity and the ratio between red and blue wavelengths to match the requirements of the test plants in the system. Given the control over grow light intensity, M‐PHIS can also be used to study the influence of different light intensities and red/blue ratio on plant growth.

Figure 4 Multispectral Plant Health Imaging System (M‐PHIS) with top cover removed and internal items shown.

Grow Lights

The design of an LED grow light / excitation light board built from the ground up was novel in its ability to have independent control over the intensities of each wavelength. LEDs have long lifetimes, require little maintenance, are relatively energy efficient and are a rapidly advancing technology area. These features make LEDs an increasingly advantageous technology for artificial lighting in plant growth systems (Folta et al., 2005) and the preferred lighting technology for M‐PHIS. Different red and blue LEDs were selected based upon previous studies of their application to plant growth (Goins et al., 1997; Porra, Thompson et Kriedemann, 1989; Schurr, Walter et Rascher, 2006; West-Eberhard, Smith et Winter, 2011). Three types of red and blue LEDs were chosen based on the peak absorption wavelengths of chlorophyll a and b; 430 to 470 nm and from 630 to 680 nm respectively. Since green light is primarily reflected by plants, only a small number of green LEDs were incorporated into the grow light board (Folta et al., 2005).

In addition to the various light combinations and ability to tune the output wavelengths, the upper and lower half of the M‐PHIS LED board can be independently controlled. This separate control is advantageous because it allows the operator to more easily illuminate the area where the plant’s leaves are located while applying less light to the roots where it is typically not required. This can result in energy savings, which is of paramount importance when designing for spaceflight experiments where power is often a limitation. The utilization of fewer LEDs also resulted in a reduction in heat generation and heat management requirements.

Figure 5 Grow / excitation light board in operation. A) All grow lights activated at 5% intensity. B) Upper section, all grow light enabled at 10%. C) Excitation lights activated at 25% D) 470 nm LEDs activated at 5%.

To better focus the energy emitted by the grow lights on the biological target, a parabolic angle was built into the LED board by employing a custom LED guide produced on a 3D printer (Figure 2.10).

Figure 6 Demonstrating Multispectral Plant Health Imaging System (M‐PHIS) grow light board parabolic angle that aids in focusing the energy emitted on the desired target

To be continued…

Several experiments were done under hypobaric conditions. They will be presented in another article following shortly.

Additional Information

For more information, see the following research article:
Abboud, Talal; Berinstain, Alain; Bamsey, Matthew; Ferl, Robert; Paul, Anna-Lisa; Graham, Thomas; Dixon, Mike; Leonardos, Demos; Stasiak, Michael; Noumeir, Rita. 2013. Multispectral Plant Health Imaging System for Space Biology and Hypobaric Plant Growth Studies. Insciences Journal –Sensors, 3(2), p. 24-44.

Or the following master’s thesis: Abboud, Talal (2013). Systèmes d’imagerie pour l’étude de la santé des plantes et la biologie spatiale. Mémoire de maîtrise électronique, Montréal, École de technologie supérieure. 90 p.