宇宙環境下における植物の成長·発達とオーキシン極性移動（Ⅱ）: 特に重力応答突然変異体ageotropumェンドウを用いた解析

摘要

Introducing mutants in graviresponse is important to know how gravity regulates morphogenesis of plants. To elucidate the role of auxin polar transport in gravimorphogenesis of plants, effects of gravistimulation on growth and development, and auxin polar transport in ageotropum pea seedlings showing abnormal gravitropic response were studied in comparison with those in Alaska pea seedlings. As well as etiolated Alaska pea epicotyls, amyloplasts sedimented to the direction of gravity were observed in ageotropum epicotyls. When embryo axes of ageotropum seeds were set in a vertical (parallel to the direction of gravity) or a horizontal (perpendicular to the direction of gravity) position and grown under 1g conditions in the dark for 6.5 days, their epicotyls showed automorphosis-like bending to the direction far from the cotyledons regardless of the conditions of seed germination. The automorphosis-like bending of etiolated ageotropum epicotyls was not affected by a simulated microgravity conditions on a 3-D clinostat. The activities of auxin polar transport of the 2nd internodes of 6.5-d-old etiolated ageotropum pea seedlings grown under 1g conditions were lower than those of Alaska pea seedlings grown under 1g conditions. The activities of auxin polar transport of the 2nd internodes in 6.5-d-old etiolated ageotropum pea seedlings were little affected by a simulated microgravity conditions on the 3-D clinostat, although those of Alaska pea seedlings were substantially affected. These results strongly support our previous idea that normal auxin polar transport is required for the normal graviresponse of epicotyls in etiolated pea seedlings.%著者らが行ったSTS-95宇宙実験や地上基礎実験において、黄化エンドゥ芽生えを宇宙微小重力環境下あるいは3次元クリノスタツト上の擬似微小重力環境下で発芽、生育させると、自発的形態形成を示すと共に、上胚軸におけるオーキシン極性移動の低下が示されている（Ueda et al. 1999, 2000, Shimazu etal. 2001, Miyamoto et al. 2005a）。さらに、地上1g環境下においてオーキシン極性移動阻害剤を外生的に投与することにより自発的形態形成に類似した成長·発達が認められた（Miyamoto et al. 2005a）。これらの結果は、オーキシン極性移動が黄化エンドゥ芽生えにおける自発的形態形成に密接に関わっていることを強く示唆する。