Roland Piquepaille's Technology Trends
How new technologies are modifying our way of life

jeudi 22 janvier 2004

According to Nature, plants seem to optimize their 'breathing' by conducting simple calculations through a distributed computing scheme. "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.

Nature adds this is similar to signals exchanged by ants to find the best source of food for an ant community.

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.

Let's come back to plants and their leaves, which have tiny pores on their surface, called stomata.

Here is a picture of a cactus leaf showing these stomata, which permit the plant to breathe when they're opened (Credit: Link).

A cactus leaf showing stomata
Leaves have openings called stomata that open wide to let CO2 in, but close up to prevent precious water vapour from escaping. Plants attempt to regulate their stomata to take in as much CO2 as 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 CO2 uptake.
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.

These results have been published by the Proceedings of the National Academy of Sciences. Here is the abstract of this paper, "Evidence for complex, collective dynamics and emergent, distributed computation in plants."

It has been suggested that some biological processes are equivalent to computation, but quantitative evidence for that view is weak. Plants must solve the problem of adjusting stomatal apertures to allow sufficient CO2 uptake for photosynthesis while preventing excessive water loss. Under some conditions, stomatal apertures become synchronized into patches that exhibit richly complicated dynamics, similar to behaviors found in cellular automata that perform computational tasks. Using sequences of chlorophyll fluorescence images from leaves of Xanthium strumarium L. (cocklebur), we quantified spatial and temporal correlations in stomatal dynamics. Our values are statistically indistinguishable from those of the same correlations found in the dynamics of automata that compute. These results are consistent with the proposition that a plant solves its optimal gas exchange problem through an emergent, distributed computation performed by its leaves.

Source: Philip Ball, Nature, January 21, 2004; and various websites

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