The twilight zone: the initiation of starch degradation in leaves

植物通过光合作用将空气中的二氧化碳转化为糖来养活自己。这些糖为植物生长提供能量和基础。虽然光合作用只能在光照下发生，但大多数植物在夜间继续生长。它们之所以能够做到这一点，是因为白天产生的一些糖以淀粉的形式储存在叶子中。到了晚上，淀粉被分解，释放出可用于生长的糖。在一天结束的时候，随着天黑，植物必须从光合作用转向淀粉分解，作为生长所需的糖的来源。我们知道这种转换在黄昏时逐渐发生。随着光线的减弱和光合作用产生的糖的供应减少，淀粉产生的糖的供应逐渐增加。然而，几乎没有人知道植物是如何实现从光合作用到淀粉分解作为糖的来源的转变的。我们发现淀粉分解是由一天结束时光线水平下降引发的。然而，令人惊讶的是，同样的光照水平下降并不会在中午引发淀粉分解。这一发现意味着植物有一种复杂的机制，可以预测夜晚何时到来，并仅在此时触发淀粉分解以应对光照水平的下降。在这个项目中，我们将研究下降的光照水平如何触发淀粉分解，以及这个过程的时间是否由植物的内部时钟（生物钟）控制。这项研究将利用突变植物，这些植物要么感知光照水平的能力降低，要么改变了其内部生物钟的功能。研究结果将提供有关植物如何在昼夜周期中保持生长的新信息，并深入了解不同的光照条件如何影响植物生产力。

Plants feed themselves by converting carbon dioxide from the air into sugars, in the process of photosynthesis. These sugars provide the energy and building blocks for plant growth. Although photosynthesis can only happen in the light, most plants continue to grow at night. They are able to do this because some of the sugars made during the day are stored in leaves as starch. At night, the starch is broken down to release sugars that can be used for growth. At the end of the day, as it gets dark, plants must switch from photosynthesis to starch breakdown as their source of sugars for growth. We know that this switch happens gradually during twilight. As the light fades and the supply of sugars from photosynthesis goes down, the supply of sugars from starch gradually increases. However, almost nothing is known about how plants bring about this transition from photosynthesis to starch breakdown as the source of sugars. We have discovered that starch breakdown is triggered by falling light levels at the end of the day. Surprisingly, however, the same fall in light levels does not trigger starch breakdown in the middle of the day. This discovery implies that plants have a sophisticated mechanism that anticipates when the night will come, and triggers starch breakdown in response to falling light levels only at that point. During this project, we will investigate how falling light levels trigger starch breakdown, and whether the timing of this process is controlled by the plant's internal clock (the circadian clock). The research will make use of mutant plants that have either a reduced ability to perceive light levels, or alterations in the functioning of their internal clock. The outcomes will be new information about how plants maintain their growth throughout the day night cycle, and insights into how different light regimes may affect plant productivity.