The influence of microgravity and spaceflight on columella cell ultrastructure in starch-deficient mutants of Arabidopsis

The ultrastructure of root cap columella cells was studied by morphometric analysis in wild-type, a reduced-starch mutant, and a starchless mutant of Arabidopsis grown in microgravity (F-mu g) and compared to ground Ig (G-1g) and Eight Ig (F-1g) controls. Seedlings of the wild-type and reduced-starc h mutant that developed during an experiment on the Space Shuttle (both the F-mu g samples and the F-1g control) exhibited a decreased starch content in comparison to the G-1g control. These results suggest that some factor a ssociated with spaceflight (and not microgravity per se) affects starch met abolism. Elevated levels of ethylene were found during the experiments on t he Space Shuttle, and analysis of ground controls with added ethylene demon strated that this gas was responsible for decreased starch levels in the co lumella cells. This is the first study to use an on-board centrifuge as a c ontrol when quantifying starch in spaceflight-grown plants. Furthermore, ou r results show that ethylene levels must be carefully considered and contro lled when designing experiments with plants for the International Space Sta tion.