Do plants act like computers?
Leaves appear to regulate their 'breathing' by conducting simple calculations.
21 January 2004
PHILIP BALL
Tiny holes in plant leaves open and close thanks to quick computations.
Plants appear to 'think', according to US researchers, who say that green plants engage in a form of problem-solving computation.
David Peak and co-workers at Utah State University in Logan say that plants may regulate their uptake and loss of gases by 'distributed computation' - a kind of information processing that involves communication between many interacting units 1.
It's the same form of maths that is widely thought to regulate how ants forage. The signals that each ant sends out to other ants, by laying down chemical trails for example, enable the ant community as a whole to find the most abundant food sources.
This might not sound much like what a computer does, but it is. In distributed computation, signals exchanged between components of the system define the process for solving a problem. Researchers are now exploring the possibility of using distributed computing with swarms of simple robots to carry out tasks, such as searching a landscape, more efficiently than a single, more sophisticated robot could manage.
Some scientists even think that distributed computation is fundamental to the way the world works. In his book A New Kind of Science, mathematician Stephen Wolfram argued that the laws of physics might arise from units of matter, space and time interacting with one another according to simple rules 2. He showed that so-called cellular automata - simple, discrete 'particles' programmed to switch between different states depending on the states of their neighbours - can mimic computers.
Peak and colleagues say that a cellular-automaton model can explain the way that plants regulate their uptake of carbon dioxide (CO 2), which they use for photosynthesis, and their loss of water vapour.
Open wide
Leaves have openings called stomata that open wide to let CO 2in, but close up to prevent precious water vapour from escaping. Plants attempt to regulate their stomata to take in as much CO 2as possible while losing the least amount of water. But they are limited in how well they can do this: leaves are often divided into patches where the stomata are either open or closed, which reduces the efficiency of CO 2uptake.
By studying the distributions of these patches of open and closed stomata in leaves of the cocklebur plant, Peak and colleagues found specific patterns reminiscent of distributed computing. Patches of open or closed stomata sometimes move around a leaf at constant speed, for example.
The statistics of the size of these patches, and of the waiting times between the appearance of successive patches, are the same as those for a model of cellular automata, the researchers say. The individual leaf stomata appear to act like simple computers, responding to what their neighbouring stomata are doing.
The researchers think that transient patchiness may be the price the plant pays for a reasonably efficient and simple way form of computation. It is a sign of the plant 'thinking' while it figures out the best solution to the problem of how much to open its stomata.
References
Peak, D. A., West, J. D., Messinger, S. M & Mott, K. A. Evidence for complex, collective dynamics and emergent, distributed computation in plants. Proceedings of the National Academy of Sciences USA ,101, 918 -922 , (2004).
Wolfram, S. A New Kind of Science (Wolfram Media Inc., 2002). |
