Nick P, Schafer E
Institut fur Biologie II der Universitat, Freiburg, Federal Republic of Germany.
Planta. 1989 Aug;179(1):123-31. doi: 10.1007/BF00395779.
Rotation of unstimulated maize (Zea mays L.) seedlings on a horizontal clinostat is accompanied by a strong bending response of the coleoptiles towards the caryopsis, yielding curvatures exceding 100 degrees. The corresponding azimuthal distribution shows two peaks, each of which is displayed by 30 degrees from the symmetry axis connecting the shortest coleoptile and caryopsis cross sections. It is argued that this spatial pattern is not the result of two independent bending preferences, but caused by a one-peaked distribution encountering an obstacle in its central part and thus being split into the two subpeaks. The existence of one preferential direction justifies considering this response to be a nastic movement. Its time course consists of an early negative phase (coleoptiles bend away from the caryopsis) followed 2 h later by a long-lasting positive bending towards the caryopsis. In light-interaction experiments, fluence-response curves for different angles between blue light and the direction of the nastic response were measured. These experiments indicate that blue light interacts with the nastic response at two levels: (i) phototonic inhibition, and (ii) addition of nastic and phototropic curvatures. It is concluded that phototropic and phototonic transduction bifurcate before the formation of phototropic transverse polarity. The additivity of nastic and phototropic responses was followed at the population level. At the level of the individual seedling, one observes, in the case of phototropic induction opposing nastic movement, three distinct responses: either strong phototropism, or nastic bending, or an "avoidance" response which involves strong curvature perpendicular to the stimulation plane. With time the nastic bending becomes increasingly stable against opposing phototropic stimulation. This can be seen from a growing proportion of seedlings exhibiting nastic bending when light is applied at variable intervals after the onset of clinostat rotation. At the transition from instability to stability, this type of experiment produces a high percentage of seedlings displaying the "avoidance" response. However, no cancelling resulting in zero curvature can be observed. It is concluded that the endogenous polarity underlying the nastic response is different in its very nature from the blue-light-elicited stable transverse polarity described earlier (Nick and Schafer 1988b).
将未受刺激的玉米（Zea mays L.）幼苗置于水平回转器上旋转时，胚芽鞘会强烈地向颖果弯曲，弯曲度超过100度。相应的方位分布呈现出两个峰值，每个峰值偏离连接最短胚芽鞘和颖果横截面的对称轴30度。有人认为，这种空间模式并非两个独立弯曲偏好的结果，而是由一个单峰分布在其中心部分遇到障碍物，从而分裂为两个子峰所致。存在一个优先方向使得可以将这种反应视为一种感性运动。其时间进程包括一个早期的负相（胚芽鞘背离颖果弯曲），随后在2小时后出现向颖果的持久正弯曲。在光相互作用实验中，测量了蓝光与感性反应方向之间不同角度的光通量 - 反应曲线。这些实验表明，蓝光在两个层面上与感性反应相互作用：（i）光子抑制，以及（ii）感性和向光性弯曲的叠加。得出的结论是，向光性和光子转导在向光性横向极性形成之前就发生了分支。在群体水平上研究了感性和向光性反应的叠加性。在个体幼苗水平上，在向光性诱导与感性运动相反的情况下，可以观察到三种不同的反应：要么是强烈的向光性，要么是感性弯曲，要么是一种“回避”反应，即涉及垂直于刺激平面的强烈弯曲。随着时间的推移，感性弯曲对相反的向光性刺激变得越来越稳定。这可以从在回转器旋转开始后以可变间隔施加光照时，表现出感性弯曲的幼苗比例不断增加中看出。在从不稳定向稳定的转变过程中，这种类型的实验会产生高比例表现出“回避”反应的幼苗。然而，未观察到曲率抵消至零的情况。得出的结论是，感性反应所基于的内源性极性在本质上与先前描述的蓝光诱导的稳定横向极性（Nick和Schafer，1988b）不同。
