Department of Metabolic Biology, John Innes Centre, Norwich NR4 7UH, United Kingdom.
Proc Natl Acad Sci U S A. 2010 May 18;107(20):9458-63. doi: 10.1073/pnas.0914299107. Epub 2010 May 3.
Plant growth is driven by photosynthetic carbon fixation during the day. Some photosynthate is accumulated, often as starch, to support nocturnal metabolism and growth at night. The rate of starch degradation in Arabidopsis leaves at night is essentially linear, and is such that almost all of the starch is used by dawn. We have investigated the timer that matches starch utilization to the duration of the night. The rate of degradation adjusted immediately and appropriately to an unexpected early onset of night. Starch was still degraded in an appropriate manner when the preceding light period was interrupted by a period of darkness. However, when Arabidopsis was grown in abnormal day lengths (28 h or 17 h) starch was exhausted approximately 24 h after the last dawn, irrespective of the actual dawn. A mutant lacking the LHY and CCA1 clock components exhausted its starch at the dawn anticipated by its fast-running circadian clock, rather than the actual dawn. Reduced growth of wild-type plants in 28-h days and lhy/cca1 mutants in 24-h days was attributable to the inappropriate rate of starch degradation and the consequent carbon starvation at the end of night. Thus, starch degradation is under circadian control to ensure that carbohydrate availability is maintained until the next anticipated dawn, and this control is necessary for maintaining plant productivity.
植物的生长是由白天的光合作用固定碳驱动的。一些光合作用产物被积累，通常以淀粉的形式，以支持夜间代谢和夜间生长。拟南芥叶片在夜间淀粉降解的速度基本上是线性的，以至于几乎所有的淀粉在黎明前都被消耗殆尽。我们研究了将淀粉利用与夜间持续时间相匹配的计时器。降解的速度会立即并适当地调整到夜间的提前开始。当先前的光照期被黑暗期打断时，淀粉仍以适当的方式降解。然而，当拟南芥在异常的日长（28 小时或 17 小时）下生长时，无论实际的黎明时间如何，淀粉大约在最后一次黎明后 24 小时就被耗尽了。缺乏 LHY 和 CCA1 时钟成分的突变体在其快速运行的生物钟预期的黎明时耗尽了淀粉，而不是实际的黎明。在 28 小时的日子里，野生型植物的生长速度减缓，而在 24 小时的日子里，lhy/cca1 突变体的生长速度减缓，这归因于淀粉降解的不当速度以及夜间结束时的碳饥饿。因此，淀粉降解受生物钟控制，以确保在预期的下一个黎明到来之前维持碳水化合物的可用性，这种控制对于维持植物的生产力是必要的。
