Schematic representation of a Euglena cell with red eyespot (9)

Schematic representation of a Chlamydomonas cell with chloroplast eyespot (4)

The eyespot apparatus (or stigma) is a photoreceptive organelle found in the flagellate (motile) cells of green algae and other unicellular photosynthetic organisms such as euglenids. It allows the cells to sense light direction and intensity and respond to it by swimming either towards the light (phototaxis) or away from the light ("photoshock" or photophobic response). This helps the cells in finding an environment with optimal light conditions for photosynthesis. Eyespots are the simplest and most common "eyes" found in nature, composed of photoreceptors and a signal transduction system generating a phototactic response.^[1] Euglena is a common Euglenophyte protist, typical of the euglenids, and commonly found in nutrient-rich freshwater, with a few marine species. ... Species See text. ... Look up stigma on Wiktionary, the free dictionary. ... Schematic of typical animal cell, showing subcellular components. ... Divisions Chlorophyta Charophyta Green algae are microscopic protists; found in all aquatic environments, including marine, freshwater and brackish water. ... A cluster of Escherichia coli bacteria magnified 10,000 times. ... The leaf is the primary site of photosynthesis in plants. ... Major groups Phototrophs    Euglenales    Eutreptiales Osmotrophs    Rhabdomonadales Phagotrophs    ?Heteronematales    ?Sphenomonadales The euglenids (also spelled euglenoids) are one of the best-known groups of flagellates, commonly found in freshwater especially when it is rich in organic materials, with a few marine and endosymbiotic members. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific context, electromagnetic radiation of any wavelength[1]. The elementary particle that defines light is the photon. ... Phototaxis is an organisms automatic movement toward or away from light. ... This article or section does not cite its references or sources. ...

Microscopic structure

Under the light microscope, eyespots appear as dark, often reddish, spots or stigmata. They get their color from the chromoproteins they contain, such as chlamyopsin, volvoxopsin or other photopigments. 1852 microscope Compound microscope made by John Cuff in 1750 A microscope (Greek: micron = small and scopos = aim) is an instrument for viewing objects that are too small to be seen by the naked or unaided eye. ...

The eyespot apparatus of Euglena comprises the paraflagellar body connecting the eyespot to the flagellum. In electron microscopy, the eyespot apparatus appears as a highly ordered lamellar structure formed by membranous rods in a helical arrangement.^[2] Euglena is a common Euglenophyte protist, typical of the euglenids, and commonly found in nutrient-rich freshwater, with a few marine species. ... // A Flagellum (plural: flagella) is a long, slender projection from the cell body, composed of microtubules and surrounded by the plasma membrane. ... This article does not cite its references or sources. ...

In Chlamydomonas, the eyespot is part of the chloroplast and takes on the appearance of a membranous sandwich structure. It is assembled from chloroplast membranes (outer, inner, and thylakoid membranes) and carotenoid-filled granules overlaid by plasma membrane. It disassembles during cell division and reforms in the daughter cells in an asymmetric fashion in relation to the cytoskeleton.^[3] Species See text. ... Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. ... Chloroplasts contain several important membranes, vital for their function. ... The orange ring surrounding Grand Prismatic Spring is due to carotenoid molecules, produced by huge mats of algae and bacteria. ... Drawing of a cell membrane A component of every biological cell, the cell membrane (or plasma membrane) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ... This does not adequately cite its references or sources. ... The eukaryotic cytoskeleton. ...

Eyespot proteins

The predominant eyespot proteins are the photoreceptor proteins that sense light. The photoreceptors found in unicellular organisms fall into two main groups: flavoproteins and retinylidene proteins (rhodopsins). Flavoproteins are characterized by containing flavin molecules as chromophores, whereas retinylidene proteins contain retinal. The photoreceptor protein in Euglena is likely a flavoprotein.^[2] In contrast, Chlamydomonas phototaxis is mediated by archaeal-type rhodopsins.^[4] Flavoproteins are proteins that contain a nucleic acid derivative of riboflavin: the Flavin-Adenine Dinucleotide or FAD. This proteins acts as dehydrogenation catalysts in biological reactions inside the mitochondria. ... Riboflavin Flavin is a vaginal ring whose biochemical smell is pungent. ... A chromophore is part (or moiety) of a molecule responsible for its color. ... Retinal, technically called retinene1 or retinaldehyde, is a light-sensitive retinene molecule found in the photoreceptor cells of the retina. ...

Besides photoreceptor proteins, eyespots contain a large number of structural, metabolic and signaling proteins. The eyespot proteome of Chlamydomonas cells consists of roughly 200 different proteins.^[5] The term proteome was coined by Mark Wilkins in 1995 (1) and is used to describe the entire complement of proteins in a given biological organism or system at a given time, i. ...

Photoreception and signal transduction

The Euglena photoreceptor was identified as a blue-light-activated adenylyl cyclase.^[6] Excitation of this receptor protein results in the formation of cyclic adenosine monophosphate (cAMP) as a second messenger. Chemical signal transduction ultimately triggers changes in flagellar beat patterns and cell movement. Adenylate cyclase (EC 4. ... Structure of cAMP cAMP represented in three ways, the left with sticks-representation, the middle with structure formula, and the right with space filled representation. ... A Second messenger system is a method of cellular signaling where the signalling molecule does not enter the cell, but rather utilizes a cascade of events that transduces the signal into a cellular change. ... This article or section does not cite its references or sources. ...

The archaeal-type rhodopsins of Chlamydomonas contain an all-trans retinylidene chromatophore which undergoes photoisomerization to a 13-cis isomer. This activates a photoreceptor channel, leading to a change in membrane potential and cellular calcium ion concentration.^[4] Photoelectric signal transduction ultimately triggers changes in flagellar strokes and thus cell movement.^[1] In chemistry, photoisomerization is molecular behavior in which structural change between isomers is caused by photoexcitation. ... This article or section is in need of attention from an expert on the subject. ...

References