Published Online: 15 SEP 2011
Copyright © 2001 John Wiley & Sons, Ltd. All rights reserved.
How to Cite
Hegemann, P. and Dieckmann, C. 2011. Algal Eyes. eLS. .
- Published Online: 15 SEP 2011
‘Vision’ is defined in a very general sense as recognition of the ambient light pattern by a motile organism and its use for orientation in a local environment. The ‘eye’ is the organ or organelle in which the light absorption and transformation into a transient intracellular signal occurs. The pigmented eyespot is functioning as the optical system that operates in most motile green algae as an interference reflecting device (quarter wave stack). In Chlorophyceae the light sensors are light-gated ion channels (Channelrhodopsin (ChR)), whereas in Euglenoida photo-activated adenylyl cyclases (PAC) fulfil this function. ChR is located within the eyespot overlaying part of the plasma membrane whereas PAC is found as a paraflagellar swelling at the basis of the long flagalla.
Motile green algae are able to detect the light direction by means of a pigmented eye.
Algal eyes are designed for detection of defuse light.
Chlorophyceae use light-gated ion channels (Channelrhodopsins) for fast depolarisation of the plasma membrane.
The depolarisation changes of the plasma membrane (PM) follow intensity changes recorded by the photoreceptor according to the orientation of the cells respective to the direction of the light source.
Depolarisation of the PM is continued to the flagellar membrane.
Flagallar membrane depolarisation causes activation of voltage gated Ca-channel and influx of Ca2+.
Intraflagellar Ca2+ changes modulate the flagellar beating pattern resulting in directional changes of the swimming.
As a sensor, Euglenoids use a photo-activated adenylyl cyclases (PAC) that produces cAMP in the light.
Since the PAC is attached to the long flagella, the produced cAMP is immediately sensed by the cAMP-regulated ion channels at the flagaller base.
The intraflagallar Ca2+ changes alter the flagellar bending and the swimming direction accordingly.