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MDA is designed as a test bed for an astrobiology field instrument to detect microbial metabolic activity in terrestrial or extraterrestrial geological soil samples. MDA employs electrochemical sensors in a unique differential chamber configuration, able to detect minute changes in the chemical composition between the two otherwise identical chambers. Both chambers are filled with identical autoclave-sterilized, sample-water mixtures. Only one of the chambers receives an additional minute, non-sterilized inoculation sample. Under the minimal assumptions that the geological sample contained nutrients (energy), organisms, and required water to initiate growth, the differential electrochemical measurements would now allow detection of metabolic activity, in addition to the electrochemical characterization of the soil samples in both chambers.

Single Loop for Cell Culture (SLCC) consists of individual, self-contained, spaceflight cell culture systems with capabilities for automated growth initiation, feeding, sub-culturing and sampling. The cells are grown and contained within a rigid cell specimen chamber (CSC). Bladder tanks provide flush and media fluid. SLCC uses active perfusion flow to provide nutrients and gas exchange, and to dilute waste products by expelling depleted media fluid into a waste bladder tank. The cells can be grown quiescently, or suspended using magnetically coupled stirrers. This paper describes the functional and safety design features, the operational modes and the spaceflight qualification processes including science validation tests, using yeast as a model organism.

This study investigated the possibility of detecting water deficit stress in plants by using optical signals collected from leaves. Two theoretical approaches have been investigated. In principle, chlorophyll fluorescence can be used to measure generally stressful situations in plants. Our review, however, found that simple ratios of coarsely time-resolved chlorophyll fluorescence, such as maximum fluorescence over fluorescence at steady state, appear to be incapable of adequately distinguishing water stress from other stress factors. A second principle being investigated involves correlation of light absorption within leaves to leaf-water-content using water absorbing and non-water absorbing wavelengths. Our investigation concentrated on defining and eliminating as many extraneous variables as possible.

Plant growth, and especially plant performance experiments in microgravity are limited by the currently available plant growth facilities (low light levels, inadequate nutrient delivery and atmosphere conditioning systems, insufficient science instrumentation, infrequent flight opportunities). In addition, mission durations of 10 to 14 days aboard the NSTS Space Shuttle allow for only brief periods of microgravity exposure with respect to the life cycle of a plant. Based on seed germination experiments (5 missions from 1992 - 1994), using the Generic BioProcessing Apparatus hardware (GBA), two new payloads have been designed specifically for plant growth. These payloads provide new opportunities for plant gravitational and space biology research and emphasize the investigation of plant performance (photosynthesis, biomass accumulation) in microgravity.

Alfalfa, clover, lettuce and periwinkle seedlings were grown from seeds during five Space Shuttle missions between 1992 and 1994. Germination was initiated on orbit. Selected plants were fixed on orbit by injecting a glutaraldehyde fixative. More than 1,000 seedlings have been grown for periods ranging from 2 to 12 days. Plants were germinated under low light conditions (1 mission) and in the dark (4 missions). The seedlings grown under low light conditions showed no significant differences in accumulated fresh mass or plant geometry between flight and ground. The plumular hook had developed both for alfalfa and clover plants. Hook opening and greening of plants occurred after the seedling penetrated the Rockwool™ substratum and were exposed to light. Microgravity seedlings exhibited an increase in curvature and bending and some plants were ‘disoriented’ in that the roots had grown into the air space above the growth medium.