Nick P, Schafer E
Frontier Research Program, Riken Institute, Wako-shi, Japan.
Planta. 1991 Oct;185(3):415-24. doi: 10.1007/BF00201066.
Phototropic stimulation induces a spatial memory. This was inferred from experiments with maize (Zea mays L.) coleoptiles involving opposing blue-light pulses, separated by variable time intervals, and rotation on a horizontal clinostat (Nick and Schafer, 1988b, Planta 175, 380-388). In those experiments, individual seedlings either curved towards the first or towards the second pulse, or they remained straight. Bending, if it occurred, seemed to be an all-or-none response. Intermediates, i.e. plants, bending only weakly, were not observed. In the first part of the present study it was attempted to create such intermediates. For this purpose the strength of the first, inducing, and the second, opposing, pulse was varied. The result was complex: (i) Individual seedlings maintained the all-or-none expression of spatial memory. (ii) However, on the level of the whole population, the time intervals at which a given response type dominated depended on the fluence ratio. (iii) Furthermore, the final curvature was determined by the fluence ratio. These results are discussed in terms of a blue-light-induced transverse polarity. This polarity initiates from a labile precursor, which can be reoriented by an opposing stimulation (indicated by the strong bending towards the second pulse). The strong curvatures towards the first pulse over long time intervals reveal that, eventually, the blue-light-induced transverse polarity becomes stabilised and thus immune to the counterpulse. In the second part of the study, the relation between phototropic transduction and transverse polarity was characterised by a phenomenological approach involving the following points: (i) Sensory adaptation for induction of transverse polarity disappears with a time course similar to that for phototropic sensory adaptatation. (ii) The fluence response for induction of transverse polarity is a saturation curve and not bell-shaped like the curve for phototropism (iii) For strong counterpulses and long time intervals the clinostat-elicited nastic response (Nick and Schafer 1989, Planta 179, 123-131) becomes manifest and causes an "aiming error" towards the caryopsis. (iv) Temperature-sensitivity of polarity induction was high in the first 20 min after induction, then dropped sharply and rose again with the approach of polarity fixation. (v) Stimulus-summation experiments indicated that, for different inducing fluences, the actual fixation of polarity happened at about 2 h after induction. These experiments point towards an early separation of the transduction chains mediating phototropism and transverse polarity, possibly before phototrophic asymmetry is formed.
向光刺激可诱导形成空间记忆。这一结论是通过对玉米（Zea mays L.）胚芽鞘进行的实验推断得出的，实验中使用了方向相反的蓝光脉冲，脉冲之间的时间间隔可变，并且在水平回转器上进行旋转（Nick和Schafer，1988b，《植物》175，380 - 388）。在这些实验中，单个幼苗要么朝着第一个脉冲弯曲，要么朝着第二个脉冲弯曲，要么保持直立。如果发生弯曲，似乎是一种全或无的反应。未观察到中间状态，即仅轻微弯曲的植株。在本研究的第一部分，试图创造出这样的中间状态。为此，改变了第一个诱导脉冲和第二个反向脉冲的强度。结果很复杂：（i）单个幼苗保持空间记忆的全或无表达。（ii）然而，在整个群体水平上，给定反应类型占主导的时间间隔取决于光通量比。（iii）此外，最终的弯曲程度由光通量比决定。这些结果根据蓝光诱导的横向极性进行了讨论。这种极性起始于一种不稳定的前体，它可通过反向刺激重新定向（由朝着第二个脉冲的强烈弯曲表明）。长时间间隔内朝着第一个脉冲的强烈弯曲表明，最终蓝光诱导的横向极性变得稳定，因此对反向脉冲免疫。在研究的第二部分，通过一种现象学方法对向光转导与横向极性之间的关系进行了表征，该方法涉及以下几点：（i）诱导横向极性的感官适应消失的时间进程与向光感官适应的相似。（ii）诱导横向极性的光通量响应是一条饱和曲线，不像向光性曲线那样呈钟形。（iii）对于强烈的反向脉冲和长时间间隔，回转器引发的感性反应（Nick和Schafer，1989，《植物》179，123 - 131）变得明显，并导致朝向颖果的“瞄准误差”。（iv）极性诱导的温度敏感性在诱导后的前20分钟内较高，然后急剧下降，并随着极性固定的临近再次上升。（v）刺激累加实验表明，对于不同的诱导光通量，极性的实际固定发生在诱导后约2小时。这些实验表明介导向光性和横向极性的转导链可能在向光性不对称形成之前就早早分离了。
