Educator Features

Plant Research Unit on the ISS
A layout of the different parts of the Plant Research Unit
The Plant Research Unit (PRU) will provide the opportunity to perform a wide array of plant experiments on board the International Space Station (ISS). Long-duration studies of plant growth, including multiple generation seed-to-seed studies, will be possible with the PRU. Such prolonged studies, performed entirely under microgravity conditions, will provide opportunities to study the effects of gravity on fundamental plant reproductive biology and development. Several short-duration experiments on the PRU are possible as well and may be combined into one increment to take advantage of research opportunities on ISS.

Image to right: Long-duration studies of plant growth will be possible with the PRU
Credit: NASA

Other possible research areas include gravity sensing, signal transduction, metabolism, photosynthesis, and transport. Growth of whole intact plants to full maturity will provide opportunities to study complex topics such as induction of woodiness and mechanisms of pathogenesis. The PRU is also capable of supporting plant tissue explants, bryophytes, algae and other lower plant forms. The PRU will be adaptable to a suite of lab support equipment including cryopreservation and tissue fixation. Diverse studies including classical and molecular genetics, anatomy, morphology, and physiology will be supported by PRU. The habitat will also provide a platform for research in crop production and biomass accumulation that will be necessary for food production and waste conversion in future, long-duration spaceflight missions.

The PRU offers a very large growing area (550 sq. cm by 38 cm tall). This volume will enable growth of large populations of plants including Apogee and Super Dwarf wheat, Brassica, Arabidopsis, and other suitable experimental subjects. The PRU will also support multiple chamber configurations, thus providing versatility in experiment designs. For example, the PRU can be configured with a single large chamber to support large population studies, or can be configured with four fully independent chambers to provide statistically significant experimental replications. Each of the individual chambers can offer fully independent control for carbon dioxide, oxygen, and ethylene regulation. Chamber root zones can be controlled for water and nutrient delivery. Chamber lighting, humidity, and temperatures can also be individually controlled. In comparison with previously flown plant growth units, the PRU will provide higher light intensity with greater uniformity and better control of environmental parameters.

In its current design, the PRU will scrub ethylene from the chamber atmosphere to a level below 5 parts per billion: this low level is intended to prevent complications previously experienced in spaceflight experiments. Ethylene will be continuously removed and degraded using a photocatalytic system. Carbon dioxide control will allow for either enrichment or removal of CO2 from the chamber atmosphere.

Consistent with other SSBRP habitats, the PRU will be housed in either a Habitat Holding Rack exposed to orbital microgravity, or on the 2.5 m Centrifuge Rotor where specimens will be exposed to .01g - 2g centrifugal accelerations. Experiments can be moved between microgravity and the centrifuge, thereby providing flexibility and true gravity controls.

The PRU is designed to be self sustaining. Once the experiment is started on Station, automatic functionality will maintain the organisms and control environmental parameters as specified in the experimental protocol. Data can be independently acquired, stored, and reported to the ground. The habitat incorporates high-resolution video and frame capture for each independent chamber. Like other SSBRP hardware, the PRU is designed with high maintainability and reliability specifications including built-in test capabilities and enhanced smart systems. A modular design concept will allow change out of components such as fluorescent and LED light sources. Up to eight habitats, each with up to four chambers, can fly simultaneously to provide a broad spectrum of experimental options and statistical validity.

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Published by the Space Station Biological Research Project
Ames Research Center