The zinnia plants began to exhibit guttation and epinasty, both signs of plant stress. Credit: NASA
When Scott Kelly tweeted a picture of moldy leaves on the current crop of zinnia flowers aboard ISS, it could have looked like the science was doomed. It was in fact an opportunity for scientists back on Earth to better understand how plants grow in microgravity, and for astronauts to practice doing what they’ll be tasked: autonomous gardening.
The Veggie plant growth facility was installed on the orbiting laboratory in early May of 2014, and the first crop – ‘Outredgrous’ red romaine lettuce – was activated for growth. The first growth cycle faced some issues. “We lost two plants due to drought stress in the first grow out and thus were very vigilant with respect to the second crop,” said Trent Smith, Veggie project manager. The 2nd crop of the same lettuce was activated in early July by astronaut Scott Kelly, and thanks to lessons learned from the first run, adjustments to watering and collecting imagery of the plants were made. The leafy greens grew according to schedule, with only one plant pillow not producing. This time the crew was able to eat the lettuce.
The next crop on the docket was a batch of zinnia flowers. “The zinnia plant is very different from lettuce, said Trent Smith. “It is more sensitive to environmental parameters and light characteristics. It has a longer growth duration between 60 and 80 days. Thus, it is a more difficult plant to grow, and allowing it to flower, along with the longer growth duration, makes it a good precursor to a tomato plant.
>2 weeks into their growth period, water was seeping out of some of the wicks – the white flaps that contain the seeds and stick out of the tops of the plant pillows. Within 10 days, scientists noted guttation on the leaves of some of the plants (ie when internal pressure builds and forces excess water out of the tips of the leaves, when a plant is experiencing high humidity + the leaves started to bend down and curl drastically = epinasty, can indicate flooding in the roots. The anomalies all pointed to inhibited air flow in the plant growth facility. So they toggled the Veggie fan from low to high. The fix had to be postponed, though, due to an unplanned spacewalk in mid-December. The affected, moldy plant tissue was cut, and stowed in -80 deg laboratory freezer (MELFI) so it could be returned to Earth and studied. The plant surfaces and plant pillow surfaces were sanitized with cleaning wipes, and the fans continued at a high speed in hopes of keeping the Veggie chamber dried out and mold growth abated.
The high fan speed was drying out the crop too much, and Kelly said he thought they needed more water. He was told, though, that the next scheduled watering was not until Dec. 27. Kelly became an autonomous gardener aboard the space station. What the Veggie team created was dubbed “The Zinnia Care Guide for the On-Orbit Gardener,” and gave basic guidelines for care while putting judgment capabilities into the hands of the astronaut. The remaining 2 plants have continued to thrive, and have even had new offshoots of buds forming.
The bud-to-petal-to-full-flower process can take about 7 to 10 days, Smith said, so flowers could be present by next week. Veggie will yield important information in preparation for a Mars mission. Studies from other isolated and confined environments, such as Antarctic stations, demonstrate the importance of plants in confinement, and how much more salient fresh food becomes psychologically, when there is little stimuli around.”
More crops for Veggie are heading to the orbiting laboratory aboard SpaceX-8. The Veg-03 run will include 2 sets of Chinese cabbage, and 1 set of red romaine lettuce. In 2018, there are plans to launch dwarf tomato seeds to the space station. Smith said the lessons learned from growing zinnia flowers will be critical in the process of growing tomatoes, a fellow flowering plant. Studies are also in progress to see how adjusting the lighting in the Veggie plant growth facility can affect plan mineral composition. There will be preflight testing to determine what “light recipe” to use aboard the station. http://www.newswise.com/articles/how-mold-on-space-station-flowers-is-helping-get-us-to-mars
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