Skopik S D, Takeda M, Cain W J, Patel N G
School of Life and Health Sciences, University of Delaware, Newark 19716.
J Biol Rhythms. 1986 Fall;1(3):243-9. doi: 10.1177/074873048600100306.
Three night-break experiment protocols were utilized in an attempt to help clarify the role of the circadian system in photoperiodic time measurement in the European corn borer, Ostrinia nubilalis. Larvae raised in a light-dark (LD) cycle consisting of 12 hr of light alternating with 12 hr of darkness (LD 12:12), at a constant temperature of 30 degrees C, enter a state of arrested growth and development known as diapause (Takeda and Skopik, 1985). In the present research (Experiment 1), the induction of diapause was prevented by 1-hr light pulses that systematically scanned the dark phase of LD 12:12. Thus, the importance of 12 hr of uninterrupted darkness for maximal induction of diapause is stressed. The same experimental protocol applied to larvae already in diapause (Experiment 2), however, resulted in a bimodal curve of diapause termination. Although this result is consistent with the proposition that a nonperiodic hourglass timer underlies this event (Skopik and Takeda, 1986), it does not rule out the circadian system. Like LD 12:12, a thermoperiod in constant darkness (12 hr at 4 degrees C alternating with 12 hr at 25 degrees C) also induces diapause. Scanning such a thermoperiod with 1-hr light pulses, however, resulted in only a small effect (reduction of diapause) when light fell in the early to middle part of the warm phase (Experiment 3). Thus, the time-measuring system, under these experimental conditions, showed only a weak response to light. This unexpected result is discussed with respect to Experiment 1 and two general models that have been proposed to account for photoperiodic time measurement in insects.
采用了三种夜间中断实验方案，试图帮助阐明昼夜节律系统在欧洲玉米螟（Ostrinia nubilalis）光周期时间测量中的作用。在30摄氏度恒温下，饲养在由12小时光照与12小时黑暗交替组成的光暗（LD）循环（LD 12:12）中的幼虫会进入一种生长和发育停滞的状态，即滞育（武田和斯科皮克，1985年）。在本研究中（实验1），通过1小时的光脉冲系统扫描LD 12:12的黑暗阶段，阻止了滞育的诱导。因此，强调了12小时不间断黑暗对于最大程度诱导滞育的重要性。然而，将相同的实验方案应用于已经处于滞育状态的幼虫（实验2），却导致了滞育终止的双峰曲线。尽管这一结果与非周期性沙漏定时器是这一事件基础的观点一致（斯科皮克和武田，1986年），但它并不排除昼夜节律系统的作用。与LD 12:12一样，在恒定黑暗中的温度周期（4摄氏度12小时与25摄氏度12小时交替）也会诱导滞育。然而，当光落在温暖阶段的早期到中期时，用1小时光脉冲扫描这样的温度周期，只产生了很小的影响（滞育减少）（实验- 3）。因此，在这些实验条件下，时间测量系统对光的反应很弱。结合实验1以及为解释昆虫光周期时间测量而提出的两个一般模型，对这一意外结果进行了讨论。
