Stankovic B, Antonsen F, Johnsson A, Volkmann D, Sack F D
Wisconsin Center for Space Automation and Robotics, University of Wisconsin, Madison, WI, USA.
Adv Space Res. 2001;27(5):915-9. doi: 10.1016/s0273-1177(01)00189-2.
The typical response of plant organs to gravistimulation is differential growth that leads to organ bending. If the gravitropic stimulus is withdrawn, endogenous compensation of the graviresponse and subsequent straightening occur in some plants. For instance, autonomic straightening of Lepidium roots occurs when gravitropically-curved rootsare rotated on a clinostat (Stankovi et al., 1998a). To determine whether endogenous compensation of the graviresponse also occurs in space, microgravity-grown cress roots were laterally centrifuged in-flight and then returned to microgravity using Biorack hardware on a shuttle mission (STS-81). The cress roots were centrifuged at 4 different g-doses (0.1 x g and 1 x g for 15 or 75 min). All four treatments yielded varying degrees of root curvature. Upon removal from the centrifuge, roots in all four treatments underwent subsequent straightening in microgravity. This straightening resulted from a loss of gravitropic curvature in older regions of the root and the coordinated alignment of new growth. These results show that both microgravity and clinostat rotation on Earth are equivalent in stimulus withdrawal with respect to the induction of endogenous compensation of the curvature. Cress roots are the only plant organ shown to undergo compensation of the curvature in both microgravity and on a clinostat. The compensation of graviresponse in space rules out the hypothesis that the endogenous root straightening ("autotropism") represents a commitment to a pre-stimulus orientation with respect to gravity and instead suggests that there is a default tendency towards axiality following a withdrawal of a g-stimulus.
植物器官对重力刺激的典型反应是差异生长，这会导致器官弯曲。如果撤去重力刺激，一些植物会发生重力反应的内源性补偿以及随后的伸直。例如，当重力弯曲的独行菜根在回转器上旋转时，会发生根的自主伸直（斯坦科维等人，1998年a）。为了确定重力反应的内源性补偿在太空中是否也会发生，在航天飞机任务（STS - 81）中，对在微重力环境下生长的水芹根在飞行中进行横向离心，然后使用生物培养箱硬件使其恢复到微重力状态。水芹根以4种不同的重力剂量（0.1xg和1xg，分别处理15分钟或75分钟）进行离心。所有这四种处理都产生了不同程度的根弯曲。从离心机中取出后，所有四种处理的根在微重力环境下都经历了随后的伸直。这种伸直是由于根的较老区域重力弯曲的丧失以及新生长部分的协调排列所致。这些结果表明，就诱导弯曲的内源性补偿而言，微重力和地球上的回转器旋转在刺激撤去方面是等效的。水芹根是唯一一种在微重力环境和回转器上都显示出弯曲补偿的植物器官。太空中重力反应的补偿排除了这样一种假设，即内源性根伸直（“自向性”）代表了对重力刺激前方向的一种定向承诺，相反，这表明在重力刺激撤去后存在一种向轴性的默认趋势。
