Block I, Briegleb W, Wolke A
DLR-Institute of Aerospace Medicine, Cologne, Germany.
J Biotechnol. 1996 Jun 27;47(2-3):239-44. doi: 10.1016/0168-1656(96)01385-5.
Free-living cells show distinct gravisensitivities and often use the gravity ('g') vector for their spatial orientation. The rhythmic contractions of the ameboid Myxomycete (acellular slime mold) Physarum polycephalum are a sensitive parameter which can be modified by external stimuli. Space experiments and ground-based 0 x g simulation studies established that the contraction period transiently decreases after a transition from 1 x g to 0 x g with a back-regulating process starting after 30 min. For determination of the threshold of acceleration sensitivity, a slow-rotating centrifuge microscope (NIZEMI--Niedergeschwindigkeits-Zentrifugenmikroskop) was used, providing in space accelerations from 0 x g to 1.5 x g. A stepwise acceleration increase revealed that the lowest acceleration level capable of inducing a response was 0.1 x g. The response to the acceleration increase was an increase in contraction period, in contrast to a stimulus deprivation, which led to a period decrease. The time schedule of the acceleration responses and back-regulating process seems to be fixed, suggesting that every acceleration being above the threshold can induce a complete response-regulation process. The low acceleration-sensitivity threshold favors rather large and dense cell organelles as candidates for the gravity receptor in Physarum.
自由生活的细胞表现出明显的重力敏感性，并且常常利用重力（“g”）矢量进行空间定向。变形虫状的黏菌（无细胞黏菌）多头绒泡菌的节律性收缩是一个敏感参数，可被外部刺激所改变。太空实验和地面零重力模拟研究表明，从1g过渡到零重力后，收缩周期会短暂缩短，30分钟后开始出现反向调节过程。为了确定加速度敏感性的阈值，使用了一台慢速旋转离心显微镜（NIZEMI——低速离心显微镜），该显微镜在太空中能提供从0g到1.5g的加速度。逐步增加加速度的实验表明，能够引发反应的最低加速度水平是0.1g。与刺激剥夺导致收缩周期缩短相反，对加速度增加的反应是收缩周期延长。加速度反应和反向调节过程的时间安排似乎是固定的，这表明任何高于阈值的加速度都能引发完整的反应调节过程。低加速度敏感性阈值表明，在多头绒泡菌中，较大且密集的细胞器更有可能是重力受体的候选者。
