Plant Vision - 100 times faster than the human eye!

Before the plant and animal kingdoms split apart, was there a common origin for our vision? German biologists suggest that the answer is 'yes' by claiming to have discovered a sense of 'animal' vision in a microscopic alga.

Chlamydomonas rheinhardtii, a single celled alga, swims with a pair of beating hairs guided by a tiny light 'sensitive' eye spot that directs it towards light but away from very bright light. The alga contains the light 'sensitive' chemical Rhodopsin, which is also found in the human retina.

Investigating this phenomenon further, Hartmann Harz and Peter Hegemann at the Max Planck Institute for Biochemistry in Martinsried, Germany, have discovered that chlamydomonas 'sees' by electric signals driven by currents of calcium ions.

Harz and Hegemann blocked these currents using the same inhibited chemicals that zoologists use to stop calcium moving through the iron channels in animal cell membranes. They detected the minute ionic currents by sucking a chlamydomonas into a fine 'tipped' electrode.

Flashing a light triggered an electric signal from the eye spot. Another electric impulse caused the beating hairs to change their pattern. By changing the solutions surrounding the alga they found that the signals were driven by calcium ions.

The speed with which the tiny organism accomplishes the task is exceptionally fast. Chlamydomonas reacts to a flash of light in less than a thousandth of a second, a hundred times faster than the human retina.

In animals, Rhodopsin triggers a cascade of chemical reactions, amplifying the signal before opening ion channels in the membrane which trigger the electrical impulse. But in the alga, the Rhodopsin seems to work by opening calcium ion channels directly.

Hegemann sees value for zoologists in studying this simple creature: "It's a very simple model for vision transduced electrically, closely related to the vision of higher animals. The next more complex system is probably a jellyfish." For evolutionists, the alga also appears to represent the ancient origin of our own vision.

Intriguing also is the question of just what it is that chlamydomonas thinks it sees when it perceives things a hundred times faster than we do!

Making Sense of Plants

"When it comes down to it, there is not much an animal can do that a plant cannot do, except, perhaps, walk around." So said Professor Malcolm Wilkins, Regis Professor of Botany at Glasgow University in a meeting of the Association for Science Education.

Wilkins stated that plants could smell, taste, see colours, tell the time, ask for water and count in a way that even computers could not. Others recognise if another plant was a friend or foe, and many of them could swim.

Wilkins, whose theories are based on established scientific facts, but who has a particularly open-minded and original approach to his subject, turned also to herbaceous plants: "Of course they grow better if you talk to them. It is actually nothing to do with what you say ... Talking to them means you are breathing carbon dioxide onto them and they like that. They may just like the vibration caused by your voice."

Professor Wilkins also said that research at Glasgow had shown that trees could ask for a drink. 'Water columns' within their trunks emitted a cracking sound, audible with a microphone, when they were running short of water. The discovery was being used to develop an automatic irrigation system.

The Venus Flytrap has not only a sense of taste - it would open again if it trapped anything other than a meaty insect - but it could count, too: 'If you touch one of its sensory hairs once, it will not react. Touch it twice and it snaps shut. The plant is able to count from nought to one to two. The most complex computer can only count zero and one.'

Professor Wilkins also suggested that plants very probably have feelings, as their surfaces are covered in electrolytes, in exactly the same way as is the skin of human beings.

Perhaps plants grow more healthily under the care of someone who has not so much a green thumb as a green mind.

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