Fixation procedure for transmission electron microscopy of Chara rhizoids under microgravity in a Spacelab (IML-2).

A special fixation device and fixation procedure have been developed to investigate for the first time the ultrastructure of gravity-sensing, unicellular Chara rhizoids grown for 30 h under microgravity (MG) conditions during the IML-2 mission. The fixation unit allowed culture, fixation and storage of Chara rhizoids in the same chamber without transferring the samples. The procedure was easy and safe to perform and required a minimum of crew time. Rhizoids fixated with glutaraldehyde in space and further processed for electron microscopy on ground showed that the fixation was of high quality and corresponded to the fixation quality of rhizoids in the ground controls. Thus, the equipment accomplished the manifold problems related to the physical effects of MG. The polarity of the rhizoids was maintained in MG. Well-preserved organelles and microtubules showed no obvious difference in ultrastructure or distribution after 30-h growth in MG compared to ground controls. The statoliths were more randomly distributed, however, only up to 50 microns basal to the tip. Thus, changing the gravity conditions does to disturb the cellular organisation of the rhizoids enabling the tip-growing cells to follow their genetic program in development and growth also under MG.