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Results obtained during the shuttle mid-deck locker experiment CHROMEX-03 suggested that failure of reproductive development of plants during spaceflight was related to a limitation in availability of metabolic gases to developing tissues due to the lack of convective air movement in microgravity. The purpose of this ground-based experiment was to determine the effect of different O2 and CO2 concentrations on plant reproductive development and growth. Fourteen day old Arabidopsis thaliana (L.) Heynh plants were grown as for the spaceflight experiment and exposed for six days to either air or one of six different air/nitrogen dilutions. Growth and reproductive responses to treatments of less than 50 mL·L-1 O2, 100 μL·L-1 CO2 were significantly different (P=0.05) from each other and all other treatments, while responses to treatments with greater than 140 mL·L-1 O2, 300 μL·L-1 CO2 were not significantly different from the air treatment.

The ASTROCULTURE™ flight unit flown as part of the SPACEHAB-03 mission on STS-63 was a complete plant growth system providing plant lighting, temperature control, humidity control, water and nutrient delivery, a CO2 control system, nutrient control using the NASA Zeoponics system, an ethylene photocatalysis unit, a control and data acquisition system, and plant video. The objective of the ASTROCULTURE™-4 experiment was to continue technological assessment of these environmental control subsystems. Plants were included in this package for the first time. Two plant species were flown, rapid cycling ‘Wisconsin Fast Plants’ (Brassica rapa), and dwarf wheat (Triticum aestivum cv. ‘Super Dwarf’). Growth and development of both plant species on orbit appeared normal and similar to that of plants grown under terrestrial conditions.