From observing a plant with a camera taking pictures at certain time intervals we can distinguish clear movement patterns typical to night and day. The experiment was done in artificial light with light period of eight hours on a wt Tomato plant which was adapted to the room for 30 days since it was brought from a greenhouse with natural light. 

Light levels do not change during the day, might the leaf movement be due to long term memory of the plant to the period of natural light growth, or is it related to water transport inside the plant which changes along with plant transpiration and water availability?

Movements during the darkness period look like some sort of leaf independent chaotic light seeking, but a noticeable preparation for the light period does takes place suggesting the existence of some sort of memory to the light turning on timepoint.

What happens inside the plant during the nocturnal movements?