Long-Term Storage of Wheat Plants for Light Microscopy 2000-01-2231

The objectives of these experiments were two fold: 1) to determine if accepted tissue fixation procedures can be adapted for long-term storage on-board the International Space Station (ISS) and 2) to test whether they are suitable for KSC Fixation Tubes (KFTs). Three tissue fixation parameters were tested: time, temperature and sample size.Fixation time:samples are normally fixed from several minutes to several hours, but because of the duration of the UF-1 mission to ISS, the tissue will be in fixative for up to 3 months. Super dwarf wheat tissue samples were fixed in either FAA (a fixative normally used for storage of plant tissues) or a glutaraldehyde-based fixative and stored for 100 days. The samples were contained in KFTs that were designed to chemically fix plant samples during spaceflight, while providing three levels of protection to crewmembers.Fixation temperature:glutaraldehyde-based fixatives are ordinarily kept at 4°C but this is not feasible for UF-1 because refrigeration on-board ISS is limited. Therefore, samples fixed at room temperature were compared to samples fixed at 4°C.Sample size:tissue is normally cut into 1–2 mm2 pieces prior to fixation to insure infiltration of the fixative, however, limited crew time may require that entire plants be fixed instead. Therefore, fixed samples of whole plants were compared to small pieces.

Results indicated that modifying these parameters to meet constraints of early ISS experimentation did not affect tissue preservation. No fixative leaks were detected from the KFTs and Spacecraft Maximum Allowable Concentration (SMAC) values were not exceeded. Therefore, KFTs can provide proper containment and fixation under expected ISS operational constraints.

However, distortion of seals and reduced performance of the KFTs were observed when FAA was used. Therefore, glutaraldehyde-based fixatives are recommended for use in this hardware.