Function of Eyespot (Stigma) in Algae

  • It is also known as Stigma.
  • Pigmented area in certain motile algae involved directly or indirectly in light perception (Bold & Wynne)
  • Cluster of lipid globules in red red colour of carotenoid
  • Location: often just beneath chromatophore membrane
  • Receiving light stimuli.
  • Eyespot which is a light-sensitive organelle, which helps the Chlamydomonas to swim toward the light. 
5 different types of eyespots based on EM studies by dodge (1969)
  • Type A: eyespot is part of chloroplast, no association with flagella in Chlorophyceae and Cryptophyceae
eyespot in chlamydomonas
  • Type B: eyespot is part of chloroplast, no association with swollen flagella in Chysophyceae, Xanthophyceae and Phaeohyceae.
  • Type C: eyespots are independent clusters of osmiophilic granules as in Euglenophyceae
eyespot in Euglena
  • Type D: osmiophilic granules of eyespot have membraneous structure as in Dinophyceae
  • Type E: Largest eyespot made up of lens, retinoid and pigmented cups family Warnowiaceae of Dinophyceae
 Eyespot proteins
•Eyespot proteins include photoreceptor protein 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
•Besides photoreceptor proteins, eyespots contain a large number of structural, metabolic and signalling proteins.
• The eyespot proteome of Chlamydomonas cells consists of roughly 200 different proteins.
Observation under microscope
  • Under microscope appear as dark orange to reddish spots. Colour from carotenoid pigment granules.
  • Readily stained with osmium tetroxide forming a black precipitate.
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