Archive for the ‘Plant Movements’ Category

Venus_flytrap.jpg“Springing the Trap”

In the previous post I suggested that the Venus flytrap works something like a mousetrap. And I described how the “trap” is hydraulically set. (For a more thorough explanation of how the Venus flytrap snaps, please see PDF file here).

But how do the trigger-hairs on the surface of the flytrap’s leaves act to “spring the trap”?

Briefly, the mechanical movement of the trigger-hairs protruding from the leaf activates mechanosensitive ion channels and generates receptor potentials that induce an action potential.

This action potential travels to the midrib of the leaf where it promotes the opening of water channels called aquaporins. This facilitates the rapid water efflux from key cells that hydraulically control the leaf opening.

More simply put, the stimulation of the leaf hairs produce electrical signals that cause the rapid deflation of the water-pressurized cells that keep the leaves open. And, thus, the “trap is sprung”.

(Please see here and here for some recent information regarding the the kinetics and mechanism of the Venus flytrap.)

ligtning_plants.jpgElectrical Signals in Plants?

Do plants have a nervous system?

The short answer is: no. (At least not the complex nervous system of animals.)

But scientists have been able to detect transient electrical signals somewhat analogous to action potentials under certain situations in plants.

Such situations involve the classic examples of thigmosnasty in plants, namely, the “touch-sensitive” plant (Mimosa pudica) and the Venus flytrap.

Charles Darwin described the Venus flytrap plant as “…one of the most wonderful in the world.” on page 231 of his book Insectivorous Plants.

Sparked by a correspondence with Darwin, which included some Venus flytrap plants, the English physiologist John Scott Burdon-Sanderson was the first to discover action potentials in plants following stimulation of a leaf. (Please see reference 1 below.)

electricity_plants.jpgDo Plants Have a Neural Net?

In addition to thigmosnastic plants, all vascular plants may be utilizing electrical signals to regulate a variety of physiological functions.

Many of the biochemical and cellular components of the neuromotoric system of animals has been found in plants. And this has led to the hypothesis that a simple neural network is present in plants, especially within phloem cells, which is responsible for the communication over long distances.

“The reason why
plants have developed pathways for electrical signal transmission
is most probably the necessity to respond rapidly to
external stimuli, for example, environmental stress factors.” (from ref 2 below)

More regarding electrical communication in plants: Novel electrical signals in plants induced by wounding

The Emerging Field of Plant Neurobiology

In 2006, an article was published in the journal Trends in Plant Science that elicited quite a kerfuffle.

This review (PDF) introduced, to the plant scientific community at least, the field of “Plant Neurobiology”. Although this proposal was not without controversy (PDF), the Society for Plant Neurobiology seems to be alive and well (Plant Neurobiology Website). (And if you happen to be in Kitakyushu, Japan, in May this year, you may be able to attend the 6th International Symposium on Plant Neurobiology).

Bottom line: Though plants don’t have a nervous system like animals, plants do have the necessary electrical, biochemical, and cellular components indicative of a neural network, albeit a relatively simple one.

1. Burdon-Sanderson J. (1873) Note on the electrical phenomena
which accompany irritation of the leaf of Dionaea muscipula.
Proceedings of the Royal Society of London 21, 495–496.
2. Fromm, J & S. Lautner (2007) Electrical signals and their physiological significance in plants. Plant, Cell and Environment 30, 249-257. (PDF)

HowPlantsWork © 2008-2011 All Rights Reserved.


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Secret_Life_Plants.gifDo Plants Have a Nervous System?

Back in the heady (hazy?) days of the early 1970’s, a book was making the rounds on college campuses that suggested plants possessed a sort of sentience.

This book was The Secret Life of Plants.

The professor teaching my Introductory Botany class at the time loathed this book. He actually stated in class that any student he caught in possession of this book would receive a grade of “F”. (True story!)

Although this prof’s reaction was perhaps an extreme example, this story serves to illustrate the general attitude within the scientific community against any suggestion that plants possess a nervous system .

The notion that plants could feel pain, for example, or move rapidly in response to stimuli was solely within the realm of science fiction. (see here and here, for example)

2703146160_61f006d6f5.jpgWhat About the Venus Flytrap?

There are, however, some examples of relatively rapid movements in some plants in response to external stimuli, the most famous of which is the Venus fly trap.

Another example is the rapid leaf movements in the touch-sensitive plant Mimosa pudica. (see a YouTube video here)

In this case, as well as in the Venus fly trap, it’s not so much that the plant is moving in response to mechanical stimulation, but that the touch is triggering a sort of spring-loaded mechanism. Think of an old-fashioned mouse trap – gently touch the triggering mechanism, and the trap snaps shut.

In these plants, however, it’s kind of a hydraulic spring-loading. That is, when some cells within a thickening at the base of the leaves called a pulvinus have a high turgor pressure, this causes the leaves to open. And if these cells lose turgor pressure, the leaves close.

But how does mechanical stimulation trigger the rapid loss of cell turgor pressure in these plants?

mouse-trap.jpg“Setting the Trap”

Plant cells, like animal cells, generate an electrical membrane potential across their cellular membranes.

In plants, this is mainly generated by converting the chemical energy of ATP into electrochemical energy by proton pumps. (Your cells use Na/K-ATPases.)

Some of the energy in this membrane potential is used by cells to accumulate solutes such as sugars and mineral ions such as potassium. This accumulation of solutes draws water into the cells via osmosis.

This is how the pulvinus cells in the Venus fly trap and the touch-sensitive plants likely generate their turgor pressure to open the leaves.

Now the leaves are hydraulically “spring-loaded”, and ready….

Next time: How electrical signals “spring the trap”. Also, an introduction to the emerging field of Plant Neurobiology.

HowPlantsWork © 2008-2011 All Rights Reserved.

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