Tuber formation in potato (Solanum tuberosum L.) under hypergravity conditions in a centrifuge and simulated microgravity (μG) conditions on a horizontal clinostat was studied using in vitro culture of single-nodal stem segments prepared from sprouting tuber shoots. Hypergravity conditions at 100 G for 6 days reduced the growth of axillary bud (or stolon) of a single-nodal stem segment; the length, diameter, and fresh weight of the stolon developed under hypergravity conditions were 53%, 66%, and 74% of 1 G control, respectively. Promotion of swelling seen in the shoot under hypergravity conditions was not observed in the stolon. The size of cells and starch grains in the epidermal tissues in the swelling stolon were reduced under hypergravity conditions. On the other hand, the length of the stolon and the size of the tuber developed in the single-nodal stem segment under simulated μG conditions on a horizontal clinostat for 3 weeks were significantly increased as compared with the 1 G control. These results suggest that stolon growth and tuber formation in the single-nodal stem segment are under the control of gravity. Further studies on the molecular mechanism how gravity regulates tuber development and starch synthesis will be required for increasing potato tuber production in space.

Soy glycinin contains a functional inhibitory sequence, DIpYNP, against muscle-atrophy-associated ubiquitin ligase Cbl-b. It inhibited the binding of Cbl-b and IRS-1 (called Cblin-like peptide) and improved denervation-induced muscle atrophy in mice. In the present study, we evaluated the anti-muscle atrophy effect by feeding Kori-tofu to a mouse model of muscle atrophy induced by sciatic nerve transection, because Kori-tofu is a freeze-dried tofu made mainly from soy proteins. In the mice fed with Kori-tofu for one week, no significant inhibition in the reduction of the tibialis anterior (TA), gastrocnemius (GA) or soleus (SOL) muscle due to denervation was observed, compared with those of mice fed a soy protein isolate (SPI) or casein. However, in the TA muscle of the Kori-tofu-fed group, a significant suppression of the increased expression levels of muscle atrophy-related genes, MAFbx/atrogin-1 and MuRF-1, induced by denervation was observed similarly as that of mice fed a SPI. Additionally, the denervation-mediated decrease in the fast-twitch type myosin heavy chain (MyHC) level was suppressed in the TA of the Kori-tofu-fed group. Thus, our results suggest that Kori-tofu could be a useful and perishable functional space food against unloading-mediated muscle atrophy.