Department of Plant Sciences, University of Western Ontario, London, Ontario, Canada.
Planta. 1972 Mar;108(1):39-57. doi: 10.1007/BF00386505.
To follow changes in the status of phytochrome in green tissue and to relate these changes to the photoperiodic control of flowering, we have used a null response technique involving 1.5-min irradiations with mixtures of different ratios of R and FR radiation.Following a main photoperiod of light from fluorescent lamps that was terminated with 5 min of R light, the proportion of Pfr in Chenopodium rubrum cotyledons was high and did not change until the 3rd hour in darkness; at this time, Pfr disappeared rapidly. When the dark period began with a 5-min irradiation with BCJ or FR light to set the proportion of Pfr low Pfr gradually reappeared during the first 3 h of darkness and then disappeared again.The timing of disappearance of Pfr is consistent with the involvement of phytochrome in photoperiodic time measurement. Reappearance of Pfr after an initial FR irradiation explains why FR irradiations sometimes fail to influence photoperiodic time measurement or only slightly hasten time measurement. A R light interruption to convert Pr to Pfr delayed, the timer by 3 h but only for interruptions after and not before the time of Pfr disappearance. Such 5-min R-light interruptions did not influence the operation of the rhythmic timekeeping mechanism. Continuous or intermittent-5 min every 1.5 h-irradiations of up to 6 h in duration were required to rephase the rhythm controlling flowering. A skeleton photoperiod of 6 h that was began and terminated by 5 or 15 min of light failed to rephase the rhythm.The shape of the curves for the rhythmic response of C. rubrum to the length of the dark period are sometimes suggestive of "clocks" operating on the principle of a tension-relaxation mechanism. Such a model allows for separate timing action of a rhythm and of Pfr disappearance over the early hours of darkness. Separate timing action does not, however, preclude an interaction between the rhythm and phytochrome in controlling flowering.
为了跟踪绿色组织中光敏色素状态的变化，并将这些变化与开花的光周期控制联系起来，我们使用了一种无反应技术，涉及用不同比例的 R 和 FR 辐射的混合物进行 1.5 分钟的辐照。在以 R 光结束的荧光灯主要光照期之后，Chenopodium rubrum 子叶中的 Pfr 比例很高，直到黑暗的第 3 小时才发生变化；此时，Pfr 迅速消失。当黑暗期以 5 分钟的 BCJ 或 FR 光照射开始，将 Pfr 的比例设置得很低时，Pfr 在黑暗的前 3 小时内逐渐重新出现，然后再次消失。Pfr 消失的时间与光敏色素参与光周期时间测量是一致的。在初始 FR 辐照后，Pfr 重新出现解释了为什么 FR 辐照有时不能影响光周期时间测量，或者只是略微加快时间测量。R 光中断将 Pr 转化为 Pfr 会使计时器延迟 3 小时，但仅适用于 Pfr 消失之后而不是之前的中断。这种 5 分钟的 R 光中断不会影响节奏计时机制的运行。要重新调整控制开花的节奏，需要进行长达 6 小时的连续或间歇性 5 分钟/次的辐照，间隔时间为 1.5 小时。一个由 5 或 15 分钟的光组成的 6 小时的骨架光周期不能重新调整节奏。C. rubrum 对黑暗期长度的节奏反应曲线的形状有时暗示着“时钟”按照张弛机制的原理运行。这种模型允许在黑暗的早期，节奏和 Pfr 消失有独立的定时作用。然而，独立的定时作用并不排除在控制开花方面，节奏和光敏色素之间的相互作用。
