Regeneration of plant cell protoplasts under microgravity: Investigation of protein patterns by SDS-PAGE and immunoblotting

As part of the D-2 Spacelab mission, tobacco (Nicotiana tabacum L.) protoplasts were cultured for 10 days in microgravity and successfully regenerated into microcalli, which, after further cultivation on the ground, gave rise to intact plants. Protein analysis was performed on samples taken during the initial microgravity period and compared to ground controls. Total protein content and protein patterns were monitored, as well as the cytoskeletal proteins tubulin and actin, a key enzyme of secondary metabolism, phenylalanine ammonia lyase, and the pathogenesis-related protein osmotin. None of the investigated proteins showed a gravity-dependent effect. Since relative changes due to culture age were detectable in the immunoblots as well as in the total protein pattern, an adaptation of the cells to microgravity without major modifications of their protein complement may be assumed.