Dose-Response Analysis of Factors Involved in Germination and Secondary Dormancy of Seeds of Sisymbrium officinale
Dose-Response Analysis of Factors Involved in Germination and Secondary Dormancy of Seeds of Sisymbrium officinale
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铁合花种子萌发及二次休眠相关因素的剂量反应分析
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H. Hilhorst
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作者：
H. Hilhorst
大蒜芥种子萌发对光照和硝酸盐有依赖性。先前已经报道了光和硝酸盐对发芽的影响之间的密切相互作用（HWM Hilhorst，CM Karssen [1988] Plant Physiol 86：591-597）。在这项研究中，一个详细的剂量-反应分析的光诱导萌发诱导次生休眠。在150 ℃黑暗培养约160小时后，水中的发芽率从90%下降到0%。在25毫摩尔KNO 3的存在下，发芽水平的下降被延迟。在24小时的时间间隔，在25毫摩尔KNO 3的存在下获得的注量响应曲线。随着预孵育时间的增加，注量-响应曲线沿着横坐标向右移动。120小时后，最高发芽水平开始下降。使用受体占有理论的公式模拟了一个简单的双分子反应的注量-响应曲线，其中反应伴侣是Pfr及其暂定受体X。当假定Pfr与X的结合具有协同性时，得到了很好的模拟。实验曲线参数可以解释为结合参数。长期以来，人们一直知道光参与许多野生物种的种子萌发。由于大多数物种研究表明，光诱导的远红外辐射的可逆性，毫无疑问，光敏色素参与。光敏色素的活性形式，Pfr，被认为是触发萌发的光需要的种子，也可能是光不依赖的种子。这些种子中预先存在的Pfr水平可能高于发芽阈值（5）。诱导次生休眠的特征是对环境因素的敏感性丧失（16）。缩写：R，红光（660 nm）; LFR，低能量密度响应; P，O，光敏色素的总水平; m，半最大萌发的对数能量密度值; B，对数剂量概率单位线的斜率; KD，解离常数; Rmax，最大响应; ke，响应与受体占有之间的比例常数;[XIT，[X]的总水平= [X] + [Pfr X]; F，光子通量（mol m-2）; n，希尔系数。皱叶酸模和马齿苋与Pfr和光敏色素受体X之间达到一定水平的相互作用后开始萌发的模型相容（9）。根据该模型，在诱导休眠过程中，降低发芽反应是活性受体X水平下降的结果，而P，ot和Pfr衰减速率保持不变。然而，在随后的研究中得出结论，R的R反应下降。暗孵育后的子种子是50%发芽所需的PfrX水平变化的结果。该水平取决于几个未知因素，但不取决于X或P0的水平。基于光敏色素分子是二聚体（23）的迹象的模型可以解释双相的能量密度-响应曲线，这是在莴苣种子敏化处理后观察到的（1，2）。该模型假设存在两种不同的光敏色素受体复合物，Pr：Pfr-X和Pfr：Pfr-X，它们分别负责极低的注量响应和LFR。提示X水平约为10 - 1 P：P，0，.此外，小于40%的X占据足以使LFR最大化。大蒜芥种子的萌发对光照和硝酸盐有绝对的需求（11，17）。详细的研究表明，光和硝酸盐之间存在强烈的相互作用（12）。这些研究是在具有一定程度休眠的种子上进行的，休眠是通过在15°C下固定的预孵育时间建立的。本研究的目的是监测R诱导次生休眠过程中的反应，并在响应的物理化学意义的变化，相对于光敏色素及其受体之间的相互作用。材料和方法
The germination of seeds of Sisymbrium officinale is lightand nitrate dependent. A close interaction between the effects of light and nitrate on germination has been reported previously (HWM Hilhorst, CM Karssen [1988] Plant Physiol 86: 591-597). In this study, a detailed dose-response analysis of the light-induced germination during induction of secondary dormancy is presented. Germination in water dropped from 90 to 0% after a dark incubation of 150C of approximately 160 hours. In the presence of 25 millimolar KNO3, the decrease in germination level was delayed. At 24-hour intervals fluence-response curves were obtained in the presence of 25 millimolar KNO3. With increasing length of the preincubation period, fluence-response curves shifted along the abscissa to the right. After 120 hours the maximal germination level started to decline. The fluence-response curves were simulated by using formulations from receptor occupancy theory for a simple bimolecular reaction in which the reaction partners were Pfr and its tentative receptor X. A good simulation was obtained when cooperativity of the binding of Pfr to X was assumed. The experimental curve parameters could then be interpreted as binding parameters. The involvement of light in the seed germination of many wild species has been known for a long time. Since the majority of the species studied show reversibility of the light induction by far-red irradiation, there is little doubt that phytochrome is involved. The active form of phytochrome, Pfr, is assumed to trigger germination of light-requiring seeds and possibly also of light-independent seeds. The levels of preexisting Pfr in these seeds may be higher than the threshold for germination (5). Induction of secondary dormancy is characterized by a loss of sensitivity to environmental factors (16). The declining response to R' after prolonged dark incubation of seeds of 'Abbreviations: R, red light (660 nm); LFR, low fluence response; P,O,, total level ofphytochrome; m, log-fluence value for half-maximal germination; B, slope of log-dose probit line; KD, dissociation constant; Rmax, maximal response; ke, proportionality constant between the response and the receptor occupancy; [XIT, total level of [X] = [X] + [Pfr X]; F, photon fluence (mol m-2); n, Hill coefficient. 1090 Rumex crispus and Portulaca oleracea was compatible with a model in which germination is initiated after attainment of a certain level of interaction between Pfr and a phytochrome receptor, X (9). According to this model, the decreasing germination response during induction of dormancy was the result of declining levels of active receptors X, while the P,ot and the Pfr decay rate remained constant. However, in a subsequent study it was concluded that the declining response to R of R. crispus seeds upon dark incubation was the result of changes in the level of PfrX required for 50% germination. This level depended on several unknown factors but not on the level ofX or P0to (8). A model based on indications that the phytochrome molecule is a dimer (23) could explain biphasic fluence-response curves, which were observed after sensitization treatments of lettuce seeds ( 1, 2). This model assumed the existence of two different active phytochrome-receptor complexes, Pr:Pfr-X and Pfr:Pfr-X, which were responsible for the very low fluence response and the LFR, respectively. Implications were that the level ofX was about lO-' P:P,0,. Moreover, occupation of less than 40% ofX was sufficient to maximize the LFR. Germination ofSisymbrium officinale seeds has an absolute requirement for light and nitrate (11, 17). Detailed studies have shown a strong interaction between light and nitrate (12). These studies were performed on seeds that possessed a degree ofdormancy established by a fixed preincubation time at 15°C. The aim of the present study was to monitor the response to R during induction of secondary dormancy and to give changes in the response a physicochemical meaning, with respect to the interaction between phytochrome and its receptor. MATERIALS AND METHODS