Zinke H
Botanisches Institut der Universität München, Müchen, Deutschland.
Planta. 1968 Mar;82(1):50-72. doi: 10.1007/BF00384697.
In the present work the influence of moist air, of sand and of several solutions on the geotropic behaviour of primary roots is studied. The course of the geotropic movement is the result of a concerted action of positive and negative reactions the intensity and duration of which differ in roots of various species.In pea roots the negative movement appears only during a short stage of development. No direct relation exists between the speed of elongation and the appearance of the negative reaction.Primary roots of Zea mays and of Pisum arvense are indifferent to thigmotropic stimuli. The negative movement has, at least in pea roots a smaller mechanically effective force than the positive movement. Therefore the negative reaction does not appear in sand because it cannot overcome the mechanical resistance of the granular medium.In liquid media pea roots react in another way than in air: here the negative reaction begins later, but it has then more influence on the course of the geotropic curvature.The influence of different cations on the geotropic behaviour and on the elongation of the roots can be understood as a combined action of the osmotic effect and of the specific ionic permeability.In pea roots the negative reaction, which appears during the time from 3 to 6 hours after the induction also depends on a definite level of turgor.Primary roots of Zea mays, which grow in a relatively large angle to the vertical line do not lose their geotropic sensibility. They react like plagiotropic organs.In pea roots relations exist between the development of the positive and the negative reaction and the presence of the cotyledons and the tip of the root.Both reactions are induced at the same time by the gravitional stimulus. Their reaction times, however, are different.The root tip is necessary for the induction of both reactions. The negative curvature also appears when the tip is cut off before the end of the reaction time.The course of the geotropic movement of primary roots is compared with the geotropic behaviour of rhizomes. As a possible explanation of both kinds of reactions a two-hormone-hypothesis is discussed.
在本研究中，研究了潮湿空气、沙子和几种溶液对初生根向地性的影响。向地运动的过程是正负反应协同作用的结果，不同物种的根中正负反应的强度和持续时间有所不同。在豌豆根中，负向运动仅出现在发育的短阶段。伸长速度与负向反应的出现之间没有直接关系。玉米和野豌豆的初生根对向触性刺激不敏感。至少在豌豆根中，负向运动的机械作用力比正向运动小。因此，在沙子中不会出现负向反应，因为它无法克服颗粒介质的机械阻力。在液体介质中，豌豆根的反应与在空气中不同：这里负向反应开始较晚，但对向地弯曲过程的影响更大。不同阳离子对根的向地性和伸长的影响可以理解为渗透效应和特定离子通透性的联合作用。在豌豆根中，诱导后3至6小时出现的负向反应也取决于一定的膨压水平。与垂直线成相对较大角度生长的玉米初生根不会丧失其向地敏感性。它们的反应类似于斜生器官。在豌豆根中，正向和负向反应的发育与子叶和根尖的存在有关。两种反应都是由重力刺激同时诱导的。然而，它们的反应时间不同。根尖是两种反应诱导所必需的。在反应时间结束前切断根尖时，也会出现负向弯曲。将初生根的向地运动过程与根茎的向地性进行了比较，并讨论了一种双激素假说作为对这两种反应的可能解释。
