Anyone who has crossed multiple time zones and is jet lagged will understand how powerful our biological clocks are. In fact, every cell in the human body has its own molecular clock capable of increasing and decreasing daily the number of many proteins that the body produces within a 24-hour cycle. The brain contains a master clock that keeps the rest of the body in sync and uses light signals from the eyes to keep up with the environment.
Plants have similar circadian rhythms that help them determine the time of day, prepare plants for pre-dawn photosynthesis, turn on heat protection mechanisms before the hottest part of the day, and produce nectar when pollinators are most likely to visit. And just like humans, every cell in the plant seems to have its own clock.
Can plants think? They might one day force us to change our definition of intelligence
But unlike humans, plants have no brain to keep their clocks in sync. How do plants coordinate their cell rhythm? Our new research shows that all cells in the plant partially coordinate by something called local self-assembly. In this way, the plant cells communicate their timing with neighboring cells, much as shoals of fish and flocks of birds coordinate their movements by interacting with their neighbors.
Earlier research showed that the time is different in different parts of a plant. These differences can be detected by measuring the timing of daily peaks in clock protein production in the various organs. These watch proteins generate the 24-hour vibrations in biological processes.
For example, just before sunrise, clock proteins activate the production of other proteins responsible for photosynthesis in leaves. We have decided to examine the watch over all the major organs of the plant to understand how plants coordinate their timing to keep the ticking of the whole plant in harmony.
What makes plants tick?
We found that in thale cress (Arabidopsis thaliana) Seedlings reaches the peak of clock proteins in each organ at different times. Organs such as leaves, roots, and stems receive different signals from their local microenvironment, such as light and temperature, and use this information to independently set their own tempo.
Do plants suffer from a kind of internal jet lag when rhythms in different organs are out of sync? While the individual clocks in different organs reach their peak at different times, this does not lead to complete chaos. Surprisingly, cells began to form spatial wave patterns in which neighboring cells are slightly in temporal succession. It's a bit like a stadium or a "Mexican" wave of sports fans standing behind the people next to them to make a wave-like movement through the crowd.
Our work shows that these waves arise from the differences between the organs as the cells begin to communicate. When the number of clock proteins in a cell reaches a peak, the cell tells its slower neighbors that follow the lead of the first cell and also produce more clock proteins. These cells then do the same with their neighbors and so on. Such patterns can be observed elsewhere in nature. Some fireflies form spatial wave patterns when they synchronize their flashes with their neighbors.
Local decision-making by cells in combination with signal transmission between them could lead to plants making decisions without a brain. It allows cells in different parts of the plant to make different decisions about growth. Cells in the shoot and root can optimize growth separately for their local conditions. The shoot can bend over where the light is not obstructed, and the roots can grow towards water or more nutrient-rich soil. It could also allow plants to survive the loss of organs through injury or be eaten by an herbivore.
This could explain how plants are able to continuously adapt their growth and development to changes in their environment that scientists call "plasticity". The understanding of how plants make decisions is not only interesting but also helps scientists to breed new plant varieties that can respond to their increasingly changing environment through climate change.