The twilight zone: the initiation of starch degradation in leaves

在光合作用过程中，植物通过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积木。虽然光合作用只能在光下进行，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树叶中。到了晚上，淀粉被分解，释放出可用于生长的糖。一天结束时，随着夜幕降临，植物必须从光合作用转变为淀粉分解，以此作为生长所需的糖来源。我们知道这种转变是在黄昏时逐渐发生的。随着光线变暗，来自光合作用的糖供应减少，来自淀粉的糖供应逐渐增加。然而，关于植物如何实现从光合作用到作为糖来源的淀粉分解的转变，人们几乎一无所知。我们已经发现，淀粉的分解是由一天结束时下降的光照水平引发的。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。这一发现表明，植物有一种复杂的机制，可以预测黑夜何时到来，只有在那个时候才会在光照水平下降时触发淀粉分解。在这个项目中，我们将研究不断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受植物内部时钟(生物钟)的控制。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，要么改变其体内时钟的功能。结果将是关于植物如何在昼夜周期中保持生长的新信息，以及对不同光照制度如何影响植物生产力的洞察。

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.