ALGAL EYESPOTJASMINE MARIYA A JDEPT. OF BOTANY ,CMS COLLEGE KOTTAYAM

EYESPOT

• Pigmented area in certain motile algae

involved directly or indirectly in

photoreception( Bold & Wynne )

• Is also known as stigma

• Cluster of lipid globules in red red colour of

carotenoid

• Often seen just beneath the chromatophore

membrane

Function :

• Receiving light stimuli

• Eyespot helps chlamydomonas to swim toward

the light

There are 5 different types of eyespots

based on EM studies by Dodge (1969)

TYPE A

Is a part of

chloroplast but has

no association with

flagella

Eg. Chlorophyceae

and cryptophyceae

The eyespot apparatus of Chlamydomonas reinhardtii in the light microscope (A1, white arrow-head), in the

transmission electron microscope (A2) and as a schematic drawing (A3). Structural intact eyespot apparatuses can be

isolated by sucrose density gradient centrifugation (B).

Eyespot apparatus of

Chlamydomonas reinhardtii

• It is composed of two highly ordered layers of carotenoid rich lipid globules inside the chloroplast

• Thee globules exhibit a remarkably a constant diameter

• They are seen subtended between thylakoidmembranes

• The outer most globule layer is attached to specialized areas of the two chloroplast envelop membranes and the adjacent plasma membrane

EM image of eyespot of chlamydomonas

TYPE B

Eyespot is a part of

chloroplast, no

association with the

swollen flagella

Eg: chrysophyceae

,xanthophyceae,

phaeophyceae

TYPE C

• Eyespots are

independent

clusters of

osmophilic

granules

Eg.

euglenophyceae

Euglina gracilis

Eyespot

E. variabilis

TYPE D

• Osmophilic

granules of

eyespots have

membraneous

structures

Eg.Dinophyceae

Eyespot of Glenodinium foliaceum

• It is seen to be situated in a ventral position at the

anterior end of the sulcus

• The eyespot is seen as a flattened sac with

rounded edges, which contains two rows of large

osmiophilic granules

• Surrounding the eyespot is a triple-membraned

envelope

• The envelope has no pores and has not been found

to be connected with the membranes of any other

organelles such as chloroplasts or nucleus.

TYPE E

• Largest eyespots

made up of

lens,retinoid and

pigmented cups

Eg.warnowiaceae

family of

dinophyceae

OCELLOID

•An ocelloid is a

subcellular structure

found in

the family Warnowiaceae

• Is analogous in structure

and function to

the eyes of multicellular

organisms

Structure of an ocelloid

• Ocelloids contain subcomponents analogous to

eye structures including the lens, cornea, iris,

and retina

• It can be divided into two substructures, the

translucent, roundish hyalosome and the

heavily pigmented melanosome, also known as

the retinal body or pigment cup

A negative staining transmission electron micrograph of an

ocelloid (white box), indicating the hyalosome (H) and retinal body (R)

• The hyalosome serves as the

refractive lens of the ocelloid; it is

surrounded by a layer

of mitochondria serving as the cornea and

has constrictive rings analogous to the iris

• The retinal body has internal structure

reminiscent of thylakoid membranes

in chloroplasts and contains proteins

related to bacteriorhodopsin, a light-

sensitive protein found in some archaea

Comparison between the structures of the ocelloid (1) and the vertebrate eye

(2). Components are indicated as the hyalosome (H), retinal body/retina (R),

and crystallin lens (C).